ADIv5: use new DAP ops for AP read/write
[fw/openocd] / src / target / arm_adi_v5.c
index 1a86458977cb177b981e10500e317f6baf12ef07..c5e0dd38a097b3500ad0f2f55f55e47906ed78af 100644 (file)
@@ -8,6 +8,8 @@
  *   Copyright (C) 2009 by Oyvind Harboe                                   *
  *   oyvind.harboe@zylin.com                                               *
  *                                                                         *
+ *   Copyright (C) 2009-2010 by David Brownell                             *
+ *                                                                         *
  *   This program is free software; you can redistribute it and/or modify  *
  *   it under the terms of the GNU General Public License as published by  *
  *   the Free Software Foundation; either version 2 of the License, or     *
  * use either SWD or JTAG, and is called SWJ-DP.  The most common type of AP
  * is used to access memory mapped resources and is called a MEM-AP.  Also a
  * JTAG-AP is also defined, bridging to JTAG resources; those are uncommon.
+ *
+ * This programming interface allows DAP pipelined operations through a
+ * transaction queue.  This primarily affects AP operations (such as using
+ * a MEM-AP to access memory or registers).  If the current transaction has
+ * not finished by the time the next one must begin, and the ORUNDETECT bit
+ * is set in the DP_CTRL_STAT register, the SSTICKYORUN status is set and
+ * further AP operations will fail.  There are two basic methods to avoid
+ * such overrun errors.  One involves polling for status instead of using
+ * transaction piplining.  The other involves adding delays to ensure the
+ * AP has enough time to complete one operation before starting the next
+ * one.  (For JTAG these delays are controlled by memaccess_tck.)
  */
 
 /*
 #include "arm_adi_v5.h"
 #include <helper/time_support.h>
 
-/*
- * Transaction Mode:
- * swjdp->trans_mode = TRANS_MODE_COMPOSITE;
- * Uses Overrun checking mode and does not do actual JTAG send/receive or transaction
- * result checking until swjdp_end_transaction()
- * This must be done before using or deallocating any return variables.
- * swjdp->trans_mode == TRANS_MODE_ATOMIC
- * All reads and writes to the AHB bus are checked for valid completion, and return values
- * are immediatley available.
-*/
-
 
 /* ARM ADI Specification requires at least 10 bits used for TAR autoincrement  */
 
@@ -117,18 +119,6 @@ static int adi_jtag_dp_scan(struct swjdp_common *swjdp,
        jtag_set_end_state(TAP_IDLE);
        arm_jtag_set_instr(jtag_info, instr, NULL);
 
-       /* Add specified number of tck clocks before accessing memory bus */
-
-       /* REVISIT these TCK cycles should be *AFTER*  updating APACC, since
-        * they provide more time for the (MEM) AP to complete the read ...
-        * See "Minimum Response Time" for JTAG-DP, in the ADIv5 spec.
-        */
-       if ((instr == JTAG_DP_APACC)
-                       && ((reg_addr == AP_REG_DRW)
-                               || ((reg_addr & 0xF0) == AP_REG_BD0))
-                       && (swjdp->memaccess_tck != 0))
-               jtag_add_runtest(swjdp->memaccess_tck, jtag_set_end_state(TAP_IDLE));
-
        /* Scan out a read or write operation using some DP or AP register.
         * For APACC access with any sticky error flag set, this is discarded.
         */
@@ -150,106 +140,80 @@ static int adi_jtag_dp_scan(struct swjdp_common *swjdp,
 
        jtag_add_dr_scan(2, fields, jtag_get_end_state());
 
-       return ERROR_OK;
+       /* Add specified number of tck clocks after starting memory bus
+        * access, giving the hardware time to complete the access.
+        * They provide more time for the (MEM) AP to complete the read ...
+        * See "Minimum Response Time" for JTAG-DP, in the ADIv5 spec.
+        */
+       if ((instr == JTAG_DP_APACC)
+                       && ((reg_addr == AP_REG_DRW)
+                               || ((reg_addr & 0xF0) == AP_REG_BD0))
+                       && (swjdp->memaccess_tck != 0))
+               jtag_add_runtest(swjdp->memaccess_tck,
+                               jtag_set_end_state(TAP_IDLE));
+
+       return jtag_get_error();
 }
 
-/* Scan out and in from host ordered uint32_t variables */
+/**
+ * Scan DPACC or APACC out and in from host ordered uint32_t buffers.
+ * This is exactly like adi_jtag_dp_scan(), except that endianness
+ * conversions are performed (so the types of invalue and outvalue
+ * must be different).
+ */
 static int adi_jtag_dp_scan_u32(struct swjdp_common *swjdp,
                uint8_t instr, uint8_t reg_addr, uint8_t RnW,
                uint32_t outvalue, uint32_t *invalue, uint8_t *ack)
 {
-       struct arm_jtag *jtag_info = swjdp->jtag_info;
-       struct scan_field fields[2];
        uint8_t out_value_buf[4];
-       uint8_t out_addr_buf;
-
-       jtag_set_end_state(TAP_IDLE);
-       arm_jtag_set_instr(jtag_info, instr, NULL);
-
-       /* Add specified number of tck clocks before accessing memory bus */
-
-       /* REVISIT these TCK cycles should be *AFTER*  updating APACC, since
-        * they provide more time for the (MEM) AP to complete the read ...
-        */
-       if ((instr == JTAG_DP_APACC)
-                       && ((reg_addr == AP_REG_DRW)
-                               || ((reg_addr & 0xF0) == AP_REG_BD0))
-                       && (swjdp->memaccess_tck != 0))
-               jtag_add_runtest(swjdp->memaccess_tck, jtag_set_end_state(TAP_IDLE));
-
-       fields[0].tap = jtag_info->tap;
-       fields[0].num_bits = 3;
-       buf_set_u32(&out_addr_buf, 0, 3, ((reg_addr >> 1) & 0x6) | (RnW & 0x1));
-       fields[0].out_value = &out_addr_buf;
-       fields[0].in_value = ack;
+       int retval;
 
-       fields[1].tap = jtag_info->tap;
-       fields[1].num_bits = 32;
        buf_set_u32(out_value_buf, 0, 32, outvalue);
-       fields[1].out_value = out_value_buf;
-       fields[1].in_value = NULL;
-
-       if (invalue)
-       {
-               fields[1].in_value = (uint8_t *)invalue;
-               jtag_add_dr_scan(2, fields, jtag_get_end_state());
 
-               jtag_add_callback(arm_le_to_h_u32, (jtag_callback_data_t) invalue);
-       } else
-       {
+       retval = adi_jtag_dp_scan(swjdp, instr, reg_addr, RnW,
+                       out_value_buf, (uint8_t *)invalue, ack);
+       if (retval != ERROR_OK)
+               return retval;
 
-               jtag_add_dr_scan(2, fields, jtag_get_end_state());
-       }
+       if (invalue)
+               jtag_add_callback(arm_le_to_h_u32,
+                               (jtag_callback_data_t) invalue);
 
-       return ERROR_OK;
+       return retval;
 }
 
-/* scan_inout_check adds one extra inscan for DPAP_READ commands to read variables */
-static int scan_inout_check(struct swjdp_common *swjdp,
-               uint8_t instr, uint8_t reg_addr, uint8_t RnW,
-               uint8_t *outvalue, uint8_t *invalue)
+/**
+ * Utility to write AP registers.
+ */
+static inline int adi_jtag_ap_write_check(struct swjdp_common *dap,
+               uint8_t reg_addr, uint8_t *outvalue)
 {
-       adi_jtag_dp_scan(swjdp, instr, reg_addr, RnW, outvalue, NULL, NULL);
-
-       if ((RnW == DPAP_READ) && (invalue != NULL))
-               adi_jtag_dp_scan(swjdp, JTAG_DP_DPACC,
-                               DP_RDBUFF, DPAP_READ, 0, invalue, &swjdp->ack);
-
-       /* In TRANS_MODE_ATOMIC all JTAG_DP_APACC transactions wait for
-        * ack = OK/FAULT and the check CTRL_STAT
-        */
-       if ((instr == JTAG_DP_APACC)
-                       && (swjdp->trans_mode == TRANS_MODE_ATOMIC))
-               return swjdp_transaction_endcheck(swjdp);
-
-       return ERROR_OK;
+       return adi_jtag_dp_scan(dap, JTAG_DP_APACC, reg_addr, DPAP_WRITE,
+                       outvalue, NULL, NULL);
 }
 
-static int scan_inout_check_u32(struct swjdp_common *swjdp,
+static int adi_jtag_scan_inout_check_u32(struct swjdp_common *swjdp,
                uint8_t instr, uint8_t reg_addr, uint8_t RnW,
                uint32_t outvalue, uint32_t *invalue)
 {
+       int retval;
+
        /* Issue the read or write */
-       adi_jtag_dp_scan_u32(swjdp, instr, reg_addr, RnW, outvalue, NULL, NULL);
+       retval = adi_jtag_dp_scan_u32(swjdp, instr, reg_addr,
+                       RnW, outvalue, NULL, NULL);
+       if (retval != ERROR_OK)
+               return retval;
 
        /* For reads,  collect posted value; RDBUFF has no other effect.
         * Assumes read gets acked with OK/FAULT, and CTRL_STAT says "OK".
         */
        if ((RnW == DPAP_READ) && (invalue != NULL))
-               adi_jtag_dp_scan_u32(swjdp, JTAG_DP_DPACC,
+               retval = adi_jtag_dp_scan_u32(swjdp, JTAG_DP_DPACC,
                                DP_RDBUFF, DPAP_READ, 0, invalue, &swjdp->ack);
-
-       /* In TRANS_MODE_ATOMIC all JTAG_DP_APACC transactions wait for
-        * ack = OK/FAULT and then check CTRL_STAT
-        */
-       if ((instr == JTAG_DP_APACC)
-                       && (swjdp->trans_mode == TRANS_MODE_ATOMIC))
-               return swjdp_transaction_endcheck(swjdp);
-
-       return ERROR_OK;
+       return retval;
 }
 
-int swjdp_transaction_endcheck(struct swjdp_common *swjdp)
+static int jtagdp_transaction_endcheck(struct swjdp_common *swjdp)
 {
        int retval;
        uint32_t ctrlstat;
@@ -258,7 +222,7 @@ int swjdp_transaction_endcheck(struct swjdp_common *swjdp)
 
 #if 0
        /* Danger!!!! BROKEN!!!! */
-       scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
+       adi_jtag_scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
                        DP_CTRL_STAT, DPAP_READ, 0, &ctrlstat);
        /* Danger!!!! BROKEN!!!! Why will jtag_execute_queue() fail here????
        R956 introduced the check on return value here and now Michael Schwingen reports
@@ -276,7 +240,7 @@ int swjdp_transaction_endcheck(struct swjdp_common *swjdp)
        /* Post CTRL/STAT read; discard any previous posted read value
         * but collect its ACK status.
         */
-       scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
+       adi_jtag_scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
                        DP_CTRL_STAT, DPAP_READ, 0, &ctrlstat);
        if ((retval = jtag_execute_queue()) != ERROR_OK)
                return retval;
@@ -305,61 +269,82 @@ int swjdp_transaction_endcheck(struct swjdp_common *swjdp)
                        }
                        else
                        {
-                               LOG_WARNING("Invalid ACK "
-                                               "in JTAG-DP transaction");
+                               LOG_WARNING("Invalid ACK %#x "
+                                               "in JTAG-DP transaction",
+                                               swjdp->ack);
                                return ERROR_JTAG_DEVICE_ERROR;
                        }
 
-                       scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
+                       adi_jtag_scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
                                        DP_CTRL_STAT, DPAP_READ, 0, &ctrlstat);
-                       if ((retval = jtag_execute_queue()) != ERROR_OK)
+                       if ((retval = dap_run(swjdp)) != ERROR_OK)
                                return retval;
                        swjdp->ack = swjdp->ack & 0x7;
                }
        }
 
+       /* REVISIT also STICKYCMP, for pushed comparisons (nyet used) */
+
        /* Check for STICKYERR and STICKYORUN */
        if (ctrlstat & (SSTICKYORUN | SSTICKYERR))
        {
-               LOG_DEBUG("swjdp: CTRL/STAT error 0x%" PRIx32 "", ctrlstat);
+               LOG_DEBUG("jtag-dp: CTRL/STAT error, 0x%" PRIx32, ctrlstat);
                /* Check power to debug regions */
                if ((ctrlstat & 0xf0000000) != 0xf0000000)
-               {
                         ahbap_debugport_init(swjdp);
-               }
                else
                {
                        uint32_t mem_ap_csw, mem_ap_tar;
 
-                       /* Print information about last AHBAP access */
-                       LOG_ERROR("AHBAP Cached values: dp_select 0x%" PRIx32 ", ap_csw 0x%" PRIx32 ", ap_tar 0x%" PRIx32 "", swjdp->dp_select_value, swjdp->ap_csw_value, swjdp->ap_tar_value);
+                       /* Maybe print information about last intended
+                        * MEM-AP access; but not if autoincrementing.
+                        * *Real* CSW and TAR values are always shown.
+                        */
+                       if (swjdp->ap_tar_value != (uint32_t) -1)
+                               LOG_DEBUG("MEM-AP Cached values: "
+                                       "ap_bank 0x%" PRIx32
+                                       ", ap_csw 0x%" PRIx32
+                                       ", ap_tar 0x%" PRIx32,
+                                       swjdp->ap_bank_value,
+                                       swjdp->ap_csw_value,
+                                       swjdp->ap_tar_value);
+
                        if (ctrlstat & SSTICKYORUN)
-                               LOG_ERROR("JTAG-DP OVERRUN - "
-                                       "check clock or reduce jtag speed");
+                               LOG_ERROR("JTAG-DP OVERRUN - check clock, "
+                                       "memaccess, or reduce jtag speed");
 
                        if (ctrlstat & SSTICKYERR)
                                LOG_ERROR("JTAG-DP STICKY ERROR");
 
                        /* Clear Sticky Error Bits */
-                       scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
+                       adi_jtag_scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
                                        DP_CTRL_STAT, DPAP_WRITE,
                                        swjdp->dp_ctrl_stat | SSTICKYORUN
                                                | SSTICKYERR, NULL);
-                       scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
+                       adi_jtag_scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
                                        DP_CTRL_STAT, DPAP_READ, 0, &ctrlstat);
-                       if ((retval = jtag_execute_queue()) != ERROR_OK)
+                       if ((retval = dap_run(swjdp)) != ERROR_OK)
+                               return retval;
+
+                       LOG_DEBUG("jtag-dp: CTRL/STAT 0x%" PRIx32, ctrlstat);
+
+                       retval = dap_queue_ap_read(swjdp,
+                                       AP_REG_CSW, &mem_ap_csw);
+                       if (retval != ERROR_OK)
                                return retval;
 
-                       LOG_DEBUG("swjdp: status 0x%" PRIx32 "", ctrlstat);
+                       retval = dap_queue_ap_read(swjdp,
+                                       AP_REG_TAR, &mem_ap_tar);
+                       if (retval != ERROR_OK)
+                               return retval;
 
-                       dap_ap_read_reg_u32(swjdp, AP_REG_CSW, &mem_ap_csw);
-                       dap_ap_read_reg_u32(swjdp, AP_REG_TAR, &mem_ap_tar);
-                       if ((retval = jtag_execute_queue()) != ERROR_OK)
+                       if ((retval = dap_run(swjdp)) != ERROR_OK)
                                return retval;
-                       LOG_ERROR("Read MEM_AP_CSW 0x%" PRIx32 ", MEM_AP_TAR 0x%" PRIx32 "", mem_ap_csw, mem_ap_tar);
+                       LOG_ERROR("MEM_AP_CSW 0x%" PRIx32 ", MEM_AP_TAR 0x%"
+                                       PRIx32, mem_ap_csw, mem_ap_tar);
 
                }
-               if ((retval = jtag_execute_queue()) != ERROR_OK)
+               if ((retval = dap_run(swjdp)) != ERROR_OK)
                        return retval;
                return ERROR_JTAG_DEVICE_ERROR;
        }
@@ -373,158 +358,176 @@ int swjdp_transaction_endcheck(struct swjdp_common *swjdp)
  *                                                                         *
 ***************************************************************************/
 
-static int dap_dp_write_reg(struct swjdp_common *swjdp,
-               uint32_t value, uint8_t reg_addr)
-{
-       return scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
-                       reg_addr, DPAP_WRITE, value, NULL);
-}
-
-static int dap_dp_read_reg(struct swjdp_common *swjdp,
-               uint32_t *value, uint8_t reg_addr)
-{
-       return scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
-                       reg_addr, DPAP_READ, 0, value);
-}
-
-int dap_ap_select(struct swjdp_common *swjdp,uint8_t apsel)
+/**
+ * Select one of the APs connected to the specified DAP.  The
+ * selection is implicitly used with future AP transactions.
+ * This is a NOP if the specified AP is already selected.
+ *
+ * @param swjdp The DAP
+ * @param apsel Number of the AP to (implicitly) use with further
+ *     transactions.  This normally identifies a MEM-AP.
+ */
+void dap_ap_select(struct swjdp_common *swjdp,uint8_t apsel)
 {
-       uint32_t select;
-       select = (apsel << 24) & 0xFF000000;
+       uint32_t select = (apsel << 24) & 0xFF000000;
 
        if (select != swjdp->apsel)
        {
                swjdp->apsel = select;
-               /* Switching AP invalidates cached values */
-               swjdp->dp_select_value = -1;
+               /* Switching AP invalidates cached values.
+                * Values MUST BE UPDATED BEFORE AP ACCESS.
+                */
+               swjdp->ap_bank_value = -1;
                swjdp->ap_csw_value = -1;
                swjdp->ap_tar_value = -1;
        }
-
-       return ERROR_OK;
-}
-
-static int dap_dp_bankselect(struct swjdp_common *swjdp, uint32_t ap_reg)
-{
-       uint32_t select;
-       select = (ap_reg & 0x000000F0);
-
-       if (select != swjdp->dp_select_value)
-       {
-               dap_dp_write_reg(swjdp, select | swjdp->apsel, DP_SELECT);
-               swjdp->dp_select_value = select;
-       }
-
-       return ERROR_OK;
 }
 
-static int dap_ap_write_reg(struct swjdp_common *swjdp,
-               uint32_t reg_addr, uint8_t *out_value_buf)
-{
-       dap_dp_bankselect(swjdp, reg_addr);
-       scan_inout_check(swjdp, JTAG_DP_APACC, reg_addr,
-                       DPAP_WRITE, out_value_buf, NULL);
-
-       return ERROR_OK;
-}
-
-int dap_ap_write_reg_u32(struct swjdp_common *swjdp, uint32_t reg_addr, uint32_t value)
-{
-       uint8_t out_value_buf[4];
-
-       buf_set_u32(out_value_buf, 0, 32, value);
-       dap_dp_bankselect(swjdp, reg_addr);
-       scan_inout_check(swjdp, JTAG_DP_APACC, reg_addr,
-                       DPAP_WRITE, out_value_buf, NULL);
-
-       return ERROR_OK;
-}
-
-int dap_ap_read_reg_u32(struct swjdp_common *swjdp, uint32_t reg_addr, uint32_t *value)
-{
-       dap_dp_bankselect(swjdp, reg_addr);
-       scan_inout_check_u32(swjdp, JTAG_DP_APACC, reg_addr,
-                       DPAP_READ, 0, value);
-
-       return ERROR_OK;
-}
-
-/***************************************************************************
- *                                                                         *
- * AHB-AP access to memory and system registers on AHB bus                 *
- *                                                                         *
-***************************************************************************/
-
+/**
+ * Queue transactions setting up transfer parameters for the
+ * currently selected MEM-AP.
+ *
+ * Subsequent transfers using registers like AP_REG_DRW or AP_REG_BD2
+ * initiate data reads or writes using memory or peripheral addresses.
+ * If the CSW is configured for it, the TAR may be automatically
+ * incremented after each transfer.
+ *
+ * @todo Rename to reflect it being specifically a MEM-AP function.
+ *
+ * @param swjdp The DAP connected to the MEM-AP.
+ * @param csw MEM-AP Control/Status Word (CSW) register to assign.  If this
+ *     matches the cached value, the register is not changed.
+ * @param tar MEM-AP Transfer Address Register (TAR) to assign.  If this
+ *     matches the cached address, the register is not changed.
+ *
+ * @return ERROR_OK if the transaction was properly queued, else a fault code.
+ */
 int dap_setup_accessport(struct swjdp_common *swjdp, uint32_t csw, uint32_t tar)
 {
+       int retval;
+
        csw = csw | CSW_DBGSWENABLE | CSW_MASTER_DEBUG | CSW_HPROT;
        if (csw != swjdp->ap_csw_value)
        {
-               /* LOG_DEBUG("swjdp : Set CSW %x",csw); */
-               dap_ap_write_reg_u32(swjdp, AP_REG_CSW, csw);
+               /* LOG_DEBUG("DAP: Set CSW %x",csw); */
+               retval = dap_queue_ap_write(swjdp, AP_REG_CSW, csw);
+               if (retval != ERROR_OK)
+                       return retval;
                swjdp->ap_csw_value = csw;
        }
        if (tar != swjdp->ap_tar_value)
        {
-               /* LOG_DEBUG("swjdp : Set TAR %x",tar); */
-               dap_ap_write_reg_u32(swjdp, AP_REG_TAR, tar);
+               /* LOG_DEBUG("DAP: Set TAR %x",tar); */
+               retval = dap_queue_ap_write(swjdp, AP_REG_TAR, tar);
+               if (retval != ERROR_OK)
+                       return retval;
                swjdp->ap_tar_value = tar;
        }
+       /* Disable TAR cache when autoincrementing */
        if (csw & CSW_ADDRINC_MASK)
-       {
-               /* Do not cache TAR value when autoincrementing */
                swjdp->ap_tar_value = -1;
-       }
        return ERROR_OK;
 }
 
-/*****************************************************************************
-*                                                                            *
-* mem_ap_read_u32(struct swjdp_common *swjdp, uint32_t address, uint32_t *value)      *
-*                                                                            *
-* Read a uint32_t value from memory or system register                            *
-* Functionally equivalent to target_read_u32(target, address, uint32_t *value),   *
-* but with less overhead                                                     *
-*****************************************************************************/
-int mem_ap_read_u32(struct swjdp_common *swjdp, uint32_t address, uint32_t *value)
+/**
+ * Asynchronous (queued) read of a word from memory or a system register.
+ *
+ * @param swjdp The DAP connected to the MEM-AP performing the read.
+ * @param address Address of the 32-bit word to read; it must be
+ *     readable by the currently selected MEM-AP.
+ * @param value points to where the word will be stored when the
+ *     transaction queue is flushed (assuming no errors).
+ *
+ * @return ERROR_OK for success.  Otherwise a fault code.
+ */
+int mem_ap_read_u32(struct swjdp_common *swjdp, uint32_t address,
+               uint32_t *value)
 {
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
+       int retval;
 
-       dap_setup_accessport(swjdp, CSW_32BIT | CSW_ADDRINC_OFF, address & 0xFFFFFFF0);
-       dap_ap_read_reg_u32(swjdp, AP_REG_BD0 | (address & 0xC), value);
+       /* Use banked addressing (REG_BDx) to avoid some link traffic
+        * (updating TAR) when reading several consecutive addresses.
+        */
+       retval = dap_setup_accessport(swjdp, CSW_32BIT | CSW_ADDRINC_OFF,
+                       address & 0xFFFFFFF0);
+       if (retval != ERROR_OK)
+               return retval;
 
-       return ERROR_OK;
+       return dap_queue_ap_read(swjdp, AP_REG_BD0 | (address & 0xC), value);
 }
 
-int mem_ap_read_atomic_u32(struct swjdp_common *swjdp, uint32_t address, uint32_t *value)
+/**
+ * Synchronous read of a word from memory or a system register.
+ * As a side effect, this flushes any queued transactions.
+ *
+ * @param swjdp The DAP connected to the MEM-AP performing the read.
+ * @param address Address of the 32-bit word to read; it must be
+ *     readable by the currently selected MEM-AP.
+ * @param value points to where the result will be stored.
+ *
+ * @return ERROR_OK for success; *value holds the result.
+ * Otherwise a fault code.
+ */
+int mem_ap_read_atomic_u32(struct swjdp_common *swjdp, uint32_t address,
+               uint32_t *value)
 {
-       mem_ap_read_u32(swjdp, address, value);
+       int retval;
+
+       retval = mem_ap_read_u32(swjdp, address, value);
+       if (retval != ERROR_OK)
+               return retval;
 
-       return swjdp_transaction_endcheck(swjdp);
+       return dap_run(swjdp);
 }
 
-/*****************************************************************************
-*                                                                            *
-* mem_ap_write_u32(struct swjdp_common *swjdp, uint32_t address, uint32_t value)      *
-*                                                                            *
-* Write a uint32_t value to memory or memory mapped register                              *
-*                                                                            *
-*****************************************************************************/
-int mem_ap_write_u32(struct swjdp_common *swjdp, uint32_t address, uint32_t value)
+/**
+ * Asynchronous (queued) write of a word to memory or a system register.
+ *
+ * @param swjdp The DAP connected to the MEM-AP.
+ * @param address Address to be written; it must be writable by
+ *     the currently selected MEM-AP.
+ * @param value Word that will be written to the address when transaction
+ *     queue is flushed (assuming no errors).
+ *
+ * @return ERROR_OK for success.  Otherwise a fault code.
+ */
+int mem_ap_write_u32(struct swjdp_common *swjdp, uint32_t address,
+               uint32_t value)
 {
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
+       int retval;
 
-       dap_setup_accessport(swjdp, CSW_32BIT | CSW_ADDRINC_OFF, address & 0xFFFFFFF0);
-       dap_ap_write_reg_u32(swjdp, AP_REG_BD0 | (address & 0xC), value);
+       /* Use banked addressing (REG_BDx) to avoid some link traffic
+        * (updating TAR) when writing several consecutive addresses.
+        */
+       retval = dap_setup_accessport(swjdp, CSW_32BIT | CSW_ADDRINC_OFF,
+                       address & 0xFFFFFFF0);
+       if (retval != ERROR_OK)
+               return retval;
 
-       return ERROR_OK;
+       return dap_queue_ap_write(swjdp, AP_REG_BD0 | (address & 0xC),
+                       value);
 }
 
-int mem_ap_write_atomic_u32(struct swjdp_common *swjdp, uint32_t address, uint32_t value)
+/**
+ * Synchronous write of a word to memory or a system register.
+ * As a side effect, this flushes any queued transactions.
+ *
+ * @param swjdp The DAP connected to the MEM-AP.
+ * @param address Address to be written; it must be writable by
+ *     the currently selected MEM-AP.
+ * @param value Word that will be written.
+ *
+ * @return ERROR_OK for success; the data was written.  Otherwise a fault code.
+ */
+int mem_ap_write_atomic_u32(struct swjdp_common *swjdp, uint32_t address,
+               uint32_t value)
 {
-       mem_ap_write_u32(swjdp, address, value);
+       int retval = mem_ap_write_u32(swjdp, address, value);
+
+       if (retval != ERROR_OK)
+               return retval;
 
-       return swjdp_transaction_endcheck(swjdp);
+       return dap_run(swjdp);
 }
 
 /*****************************************************************************
@@ -540,8 +543,6 @@ int mem_ap_write_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
        uint32_t adr = address;
        uint8_t* pBuffer = buffer;
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        count >>= 2;
        wcount = count;
 
@@ -579,10 +580,13 @@ int mem_ap_write_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
 
                for (writecount = 0; writecount < blocksize; writecount++)
                {
-                       dap_ap_write_reg(swjdp, AP_REG_DRW, buffer + 4 * writecount);
+                       retval = dap_queue_ap_write(swjdp, AP_REG_DRW,
+                               *(uint32_t *) (buffer + 4 * writecount));
+                       if (retval != ERROR_OK)
+                               break;
                }
 
-               if (swjdp_transaction_endcheck(swjdp) == ERROR_OK)
+               if (dap_run(swjdp) == ERROR_OK)
                {
                        wcount = wcount - blocksize;
                        address = address + 4 * blocksize;
@@ -596,6 +600,7 @@ int mem_ap_write_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
                if (errorcount > 1)
                {
                        LOG_WARNING("Block write error address 0x%" PRIx32 ", wcount 0x%x", address, wcount);
+                       /* REVISIT return the *actual* fault code */
                        return ERROR_JTAG_DEVICE_ERROR;
                }
        }
@@ -609,8 +614,6 @@ static int mem_ap_write_buf_packed_u16(struct swjdp_common *swjdp,
        int retval = ERROR_OK;
        int wcount, blocksize, writecount, i;
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        wcount = count >> 1;
 
        while (wcount > 0)
@@ -636,9 +639,12 @@ static int mem_ap_write_buf_packed_u16(struct swjdp_common *swjdp,
 
                        if (nbytes < 4)
                        {
-                               if (mem_ap_write_buf_u16(swjdp, buffer, nbytes, address) != ERROR_OK)
+                               if (mem_ap_write_buf_u16(swjdp, buffer,
+                                               nbytes, address) != ERROR_OK)
                                {
-                                       LOG_WARNING("Block read error address 0x%" PRIx32 ", count 0x%x", address, count);
+                                       LOG_WARNING("Block write error address "
+                                               "0x%" PRIx32 ", count 0x%x",
+                                               address, count);
                                        return ERROR_JTAG_DEVICE_ERROR;
                                }
 
@@ -657,10 +663,17 @@ static int mem_ap_write_buf_packed_u16(struct swjdp_common *swjdp,
                                }
 
                                memcpy(&outvalue, buffer, sizeof(uint32_t));
-                               dap_ap_write_reg_u32(swjdp, AP_REG_DRW, outvalue);
-                               if (swjdp_transaction_endcheck(swjdp) != ERROR_OK)
+                               retval = dap_queue_ap_write(swjdp,
+                                               AP_REG_DRW, outvalue);
+                               if (retval != ERROR_OK)
+                                       break;
+
+                               if (dap_run(swjdp) != ERROR_OK)
                                {
-                                       LOG_WARNING("Block read error address 0x%" PRIx32 ", count 0x%x", address, count);
+                                       LOG_WARNING("Block write error address "
+                                               "0x%" PRIx32 ", count 0x%x",
+                                               address, count);
+                                       /* REVISIT return *actual* fault code */
                                        return ERROR_JTAG_DEVICE_ERROR;
                                }
                        }
@@ -682,16 +695,20 @@ int mem_ap_write_buf_u16(struct swjdp_common *swjdp, uint8_t *buffer, int count,
        if (count >= 4)
                return mem_ap_write_buf_packed_u16(swjdp, buffer, count, address);
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        while (count > 0)
        {
                dap_setup_accessport(swjdp, CSW_16BIT | CSW_ADDRINC_SINGLE, address);
                uint16_t svalue;
                memcpy(&svalue, buffer, sizeof(uint16_t));
                uint32_t outvalue = (uint32_t)svalue << 8 * (address & 0x3);
-               dap_ap_write_reg_u32(swjdp, AP_REG_DRW, outvalue);
-               retval = swjdp_transaction_endcheck(swjdp);
+               retval = dap_queue_ap_write(swjdp, AP_REG_DRW, outvalue);
+               if (retval != ERROR_OK)
+                       break;
+
+               retval = dap_run(swjdp);
+               if (retval != ERROR_OK)
+                       break;
+
                count -= 2;
                address += 2;
                buffer += 2;
@@ -706,8 +723,6 @@ static int mem_ap_write_buf_packed_u8(struct swjdp_common *swjdp,
        int retval = ERROR_OK;
        int wcount, blocksize, writecount, i;
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        wcount = count;
 
        while (wcount > 0)
@@ -731,7 +746,9 @@ static int mem_ap_write_buf_packed_u8(struct swjdp_common *swjdp,
                        {
                                if (mem_ap_write_buf_u8(swjdp, buffer, nbytes, address) != ERROR_OK)
                                {
-                                       LOG_WARNING("Block read error address 0x%" PRIx32 ", count 0x%x", address, count);
+                                       LOG_WARNING("Block write error address "
+                                               "0x%" PRIx32 ", count 0x%x",
+                                               address, count);
                                        return ERROR_JTAG_DEVICE_ERROR;
                                }
 
@@ -750,10 +767,17 @@ static int mem_ap_write_buf_packed_u8(struct swjdp_common *swjdp,
                                }
 
                                memcpy(&outvalue, buffer, sizeof(uint32_t));
-                               dap_ap_write_reg_u32(swjdp, AP_REG_DRW, outvalue);
-                               if (swjdp_transaction_endcheck(swjdp) != ERROR_OK)
+                               retval = dap_queue_ap_write(swjdp,
+                                               AP_REG_DRW, outvalue);
+                               if (retval != ERROR_OK)
+                                       break;
+
+                               if (dap_run(swjdp) != ERROR_OK)
                                {
-                                       LOG_WARNING("Block read error address 0x%" PRIx32 ", count 0x%x", address, count);
+                                       LOG_WARNING("Block write error address "
+                                               "0x%" PRIx32 ", count 0x%x",
+                                               address, count);
+                                       /* REVISIT return *actual* fault code */
                                        return ERROR_JTAG_DEVICE_ERROR;
                                }
                        }
@@ -775,14 +799,18 @@ int mem_ap_write_buf_u8(struct swjdp_common *swjdp, uint8_t *buffer, int count,
        if (count >= 4)
                return mem_ap_write_buf_packed_u8(swjdp, buffer, count, address);
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        while (count > 0)
        {
                dap_setup_accessport(swjdp, CSW_8BIT | CSW_ADDRINC_SINGLE, address);
                uint32_t outvalue = (uint32_t)*buffer << 8 * (address & 0x3);
-               dap_ap_write_reg_u32(swjdp, AP_REG_DRW, outvalue);
-               retval = swjdp_transaction_endcheck(swjdp);
+               retval = dap_queue_ap_write(swjdp, AP_REG_DRW, outvalue);
+               if (retval != ERROR_OK)
+                       break;
+
+               retval = dap_run(swjdp);
+               if (retval != ERROR_OK)
+                       break;
+
                count--;
                address++;
                buffer++;
@@ -791,28 +819,32 @@ int mem_ap_write_buf_u8(struct swjdp_common *swjdp, uint8_t *buffer, int count,
        return retval;
 }
 
-/*********************************************************************************
-*                                                                                *
-* mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count, uint32_t address)  *
-*                                                                                *
-* Read block fast in target order (little endian) into a buffer                  *
-*                                                                                *
-**********************************************************************************/
-int mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count, uint32_t address)
+/**
+ * Synchronously read a block of 32-bit words into a buffer
+ * @param swjdp The DAP connected to the MEM-AP.
+ * @param buffer where the words will be stored (in host byte order).
+ * @param count How many words to read.
+ * @param address Memory address from which to read words; all the
+ *     words must be readable by the currently selected MEM-AP.
+ */
+int mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer,
+               int count, uint32_t address)
 {
        int wcount, blocksize, readcount, errorcount = 0, retval = ERROR_OK;
        uint32_t adr = address;
        uint8_t* pBuffer = buffer;
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        count >>= 2;
        wcount = count;
 
        while (wcount > 0)
        {
-               /* Adjust to read blocks within boundaries aligned to the TAR autoincremnent size*/
-               blocksize = max_tar_block_size(swjdp->tar_autoincr_block, address);
+               /* Adjust to read blocks within boundaries aligned to the
+                * TAR autoincrement size (at least 2^10).  Autoincrement
+                * mode avoids an extra per-word roundtrip to update TAR.
+                */
+               blocksize = max_tar_block_size(swjdp->tar_autoincr_block,
+                               address);
                if (wcount < blocksize)
                        blocksize = wcount;
 
@@ -820,7 +852,15 @@ int mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
                if (blocksize == 0)
                        blocksize = 1;
 
-               dap_setup_accessport(swjdp, CSW_32BIT | CSW_ADDRINC_SINGLE, address);
+               dap_setup_accessport(swjdp, CSW_32BIT | CSW_ADDRINC_SINGLE,
+                               address);
+
+               /* FIXME remove these three calls to adi_jtag_dp_scan(),
+                * so this routine becomes transport-neutral.  Be careful
+                * not to cause performance problems with JTAG; would it
+                * suffice to loop over dap_queue_ap_read(), or would that
+                * be slower when JTAG is the chosen transport?
+                */
 
                /* Scan out first read */
                adi_jtag_dp_scan(swjdp, JTAG_DP_APACC, AP_REG_DRW,
@@ -842,7 +882,7 @@ int mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
                adi_jtag_dp_scan(swjdp, JTAG_DP_DPACC, DP_RDBUFF,
                                DPAP_READ, 0, buffer + 4 * readcount,
                                &swjdp->ack);
-               if (swjdp_transaction_endcheck(swjdp) == ERROR_OK)
+               if (dap_run(swjdp) == ERROR_OK)
                {
                        wcount = wcount - blocksize;
                        address += 4 * blocksize;
@@ -855,7 +895,9 @@ int mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
 
                if (errorcount > 1)
                {
-                       LOG_WARNING("Block read error address 0x%" PRIx32 ", count 0x%x", address, count);
+                       LOG_WARNING("Block read error address 0x%" PRIx32
+                               ", count 0x%x", address, count);
+                       /* REVISIT return the *actual* fault code */
                        return ERROR_JTAG_DEVICE_ERROR;
                }
        }
@@ -871,7 +913,8 @@ int mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
 
                        for (i = 0; i < 4; i++)
                        {
-                               *((uint8_t*)pBuffer) = (data >> 8 * (adr & 0x3));
+                               *((uint8_t*)pBuffer) =
+                                               (data >> 8 * (adr & 0x3));
                                pBuffer++;
                                adr++;
                        }
@@ -888,8 +931,6 @@ static int mem_ap_read_buf_packed_u16(struct swjdp_common *swjdp,
        int retval = ERROR_OK;
        int wcount, blocksize, readcount, i;
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        wcount = count >> 1;
 
        while (wcount > 0)
@@ -910,10 +951,11 @@ static int mem_ap_read_buf_packed_u16(struct swjdp_common *swjdp,
 
                do
                {
-                       dap_ap_read_reg_u32(swjdp, AP_REG_DRW, &invalue);
-                       if (swjdp_transaction_endcheck(swjdp) != ERROR_OK)
+                       retval = dap_queue_ap_read(swjdp, AP_REG_DRW, &invalue);
+                       if (dap_run(swjdp) != ERROR_OK)
                        {
                                LOG_WARNING("Block read error address 0x%" PRIx32 ", count 0x%x", address, count);
+                               /* REVISIT return the *actual* fault code */
                                return ERROR_JTAG_DEVICE_ERROR;
                        }
 
@@ -934,7 +976,16 @@ static int mem_ap_read_buf_packed_u16(struct swjdp_common *swjdp,
        return retval;
 }
 
-int mem_ap_read_buf_u16(struct swjdp_common *swjdp, uint8_t *buffer, int count, uint32_t address)
+/**
+ * Synchronously read a block of 16-bit halfwords into a buffer
+ * @param swjdp The DAP connected to the MEM-AP.
+ * @param buffer where the halfwords will be stored (in host byte order).
+ * @param count How many halfwords to read.
+ * @param address Memory address from which to read words; all the
+ *     words must be readable by the currently selected MEM-AP.
+ */
+int mem_ap_read_buf_u16(struct swjdp_common *swjdp, uint8_t *buffer,
+               int count, uint32_t address)
 {
        uint32_t invalue, i;
        int retval = ERROR_OK;
@@ -942,13 +993,17 @@ int mem_ap_read_buf_u16(struct swjdp_common *swjdp, uint8_t *buffer, int count,
        if (count >= 4)
                return mem_ap_read_buf_packed_u16(swjdp, buffer, count, address);
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        while (count > 0)
        {
                dap_setup_accessport(swjdp, CSW_16BIT | CSW_ADDRINC_SINGLE, address);
-               dap_ap_read_reg_u32(swjdp, AP_REG_DRW, &invalue);
-               retval = swjdp_transaction_endcheck(swjdp);
+               retval = dap_queue_ap_read(swjdp, AP_REG_DRW, &invalue);
+               if (retval != ERROR_OK)
+                       break;
+
+               retval = dap_run(swjdp);
+               if (retval != ERROR_OK)
+                       break;
+
                if (address & 0x1)
                {
                        for (i = 0; i < 2; i++)
@@ -984,8 +1039,6 @@ static int mem_ap_read_buf_packed_u8(struct swjdp_common *swjdp,
        int retval = ERROR_OK;
        int wcount, blocksize, readcount, i;
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        wcount = count;
 
        while (wcount > 0)
@@ -1003,10 +1056,11 @@ static int mem_ap_read_buf_packed_u8(struct swjdp_common *swjdp,
 
                do
                {
-                       dap_ap_read_reg_u32(swjdp, AP_REG_DRW, &invalue);
-                       if (swjdp_transaction_endcheck(swjdp) != ERROR_OK)
+                       retval = dap_queue_ap_read(swjdp, AP_REG_DRW, &invalue);
+                       if (dap_run(swjdp) != ERROR_OK)
                        {
                                LOG_WARNING("Block read error address 0x%" PRIx32 ", count 0x%x", address, count);
+                               /* REVISIT return the *actual* fault code */
                                return ERROR_JTAG_DEVICE_ERROR;
                        }
 
@@ -1027,7 +1081,16 @@ static int mem_ap_read_buf_packed_u8(struct swjdp_common *swjdp,
        return retval;
 }
 
-int mem_ap_read_buf_u8(struct swjdp_common *swjdp, uint8_t *buffer, int count, uint32_t address)
+/**
+ * Synchronously read a block of bytes into a buffer
+ * @param swjdp The DAP connected to the MEM-AP.
+ * @param buffer where the bytes will be stored.
+ * @param count How many bytes to read.
+ * @param address Memory address from which to read data; all the
+ *     data must be readable by the currently selected MEM-AP.
+ */
+int mem_ap_read_buf_u8(struct swjdp_common *swjdp, uint8_t *buffer,
+               int count, uint32_t address)
 {
        uint32_t invalue;
        int retval = ERROR_OK;
@@ -1035,13 +1098,14 @@ int mem_ap_read_buf_u8(struct swjdp_common *swjdp, uint8_t *buffer, int count, u
        if (count >= 4)
                return mem_ap_read_buf_packed_u8(swjdp, buffer, count, address);
 
-       swjdp->trans_mode = TRANS_MODE_COMPOSITE;
-
        while (count > 0)
        {
                dap_setup_accessport(swjdp, CSW_8BIT | CSW_ADDRINC_SINGLE, address);
-               dap_ap_read_reg_u32(swjdp, AP_REG_DRW, &invalue);
-               retval = swjdp_transaction_endcheck(swjdp);
+               retval = dap_queue_ap_read(swjdp, AP_REG_DRW, &invalue);
+               retval = dap_run(swjdp);
+               if (retval != ERROR_OK)
+                       break;
+
                *((uint8_t*)buffer) = (invalue >> 8 * (address & 0x3));
                count--;
                address++;
@@ -1051,12 +1115,127 @@ int mem_ap_read_buf_u8(struct swjdp_common *swjdp, uint8_t *buffer, int count, u
        return retval;
 }
 
+/*--------------------------------------------------------------------------*/
+
+static int jtag_idcode_q_read(struct swjdp_common *dap,
+               uint8_t *ack, uint32_t *data)
+{
+       struct arm_jtag *jtag_info = dap->jtag_info;
+       int retval;
+       struct scan_field fields[1];
+
+       jtag_set_end_state(TAP_IDLE);
+
+       /* This is a standard JTAG operation -- no DAP tweakage */
+       retval = arm_jtag_set_instr(jtag_info, JTAG_DP_IDCODE, NULL);
+       if (retval != ERROR_OK)
+               return retval;
+
+       fields[0].tap = jtag_info->tap;
+       fields[0].num_bits = 32;
+       fields[0].out_value = NULL;
+       fields[0].in_value = (void *) data;
+
+       jtag_add_dr_scan(1, fields, jtag_get_end_state());
+       retval = jtag_get_error();
+       if (retval != ERROR_OK)
+               return retval;
+
+       jtag_add_callback(arm_le_to_h_u32,
+                       (jtag_callback_data_t) data);
+
+       return retval;
+}
+
+static int jtag_dp_q_read(struct swjdp_common *dap, unsigned reg,
+               uint32_t *data)
+{
+       return adi_jtag_scan_inout_check_u32(dap, JTAG_DP_DPACC,
+                       reg, DPAP_READ, 0, data);
+}
+
+static int jtag_dp_q_write(struct swjdp_common *dap, unsigned reg,
+               uint32_t data)
+{
+       return adi_jtag_scan_inout_check_u32(dap, JTAG_DP_DPACC,
+                       reg, DPAP_WRITE, data, NULL);
+}
+
+/** Select the AP register bank matching bits 7:4 of reg. */
+static int jtag_ap_q_bankselect(struct swjdp_common *dap, unsigned reg)
+{
+       uint32_t select = reg & 0x000000F0;
+
+       if (select == dap->ap_bank_value)
+               return ERROR_OK;
+       dap->ap_bank_value = select;
+
+       select |= dap->apsel;
+
+       return jtag_dp_q_write(dap, DP_SELECT, select);
+}
+
+static int jtag_ap_q_read(struct swjdp_common *dap, unsigned reg,
+               uint32_t *data)
+{
+       int retval = jtag_ap_q_bankselect(dap, reg);
+
+       if (retval != ERROR_OK)
+               return retval;
+
+       return adi_jtag_scan_inout_check_u32(dap, JTAG_DP_APACC, reg,
+                       DPAP_READ, 0, data);
+}
+
+static int jtag_ap_q_write(struct swjdp_common *dap, unsigned reg,
+               uint32_t data)
+{
+       uint8_t out_value_buf[4];
+
+       int retval = jtag_ap_q_bankselect(dap, reg);
+       if (retval != ERROR_OK)
+               return retval;
+
+       buf_set_u32(out_value_buf, 0, 32, data);
+
+       return adi_jtag_ap_write_check(dap, reg, out_value_buf);
+}
+
+static int jtag_ap_q_abort(struct swjdp_common *dap, uint8_t *ack)
+{
+       /* for JTAG, this is the only valid ABORT register operation */
+       return adi_jtag_dp_scan_u32(dap, JTAG_DP_ABORT,
+                       0, DPAP_WRITE, 1, NULL, ack);
+}
+
+static int jtag_dp_run(struct swjdp_common *dap)
+{
+       return jtagdp_transaction_endcheck(dap);
+}
+
+static const struct dap_ops jtag_dp_ops = {
+       .queue_idcode_read =    jtag_idcode_q_read,
+       .queue_dp_read =        jtag_dp_q_read,
+       .queue_dp_write =       jtag_dp_q_write,
+       .queue_ap_read =        jtag_ap_q_read,
+       .queue_ap_write =       jtag_ap_q_write,
+       .queue_ap_abort =       jtag_ap_q_abort,
+       .run =                  jtag_dp_run,
+};
+
+/*--------------------------------------------------------------------------*/
+
 /**
- * Initialize a DAP.
+ * Initialize a DAP.  This sets up the power domains, prepares the DP
+ * for further use, and arranges to use AP #0 for all AP operations
+ * until dap_ap-select() changes that policy.
+ *
+ * @param swjdp The DAP being initialized.
  *
  * @todo Rename this.  We also need an initialization scheme which account
  * for SWD transports not just JTAG; that will need to address differences
  * in layering.  (JTAG is useful without any debug target; but not SWD.)
+ * And this may not even use an AHB-AP ... e.g. DAP-Lite uses an APB-AP.
  */
 int ahbap_debugport_init(struct swjdp_common *swjdp)
 {
@@ -1067,53 +1246,77 @@ int ahbap_debugport_init(struct swjdp_common *swjdp)
 
        LOG_DEBUG(" ");
 
+       /* JTAG-DP or SWJ-DP, in JTAG mode */
+       swjdp->ops = &jtag_dp_ops;
+
        /* Default MEM-AP setup.
         *
         * REVISIT AP #0 may be an inappropriate default for this.
-        * Should we probe, or receve a hint from the caller?
+        * Should we probe, or take a hint from the caller?
         * Presumably we can ignore the possibility of multiple APs.
         */
-       swjdp->apsel = 0;
-       swjdp->ap_csw_value = -1;
-       swjdp->ap_tar_value = -1;
+       swjdp->apsel = !0;
+       dap_ap_select(swjdp, 0);
 
        /* DP initialization */
-       swjdp->trans_mode = TRANS_MODE_ATOMIC;
-       dap_dp_read_reg(swjdp, &dummy, DP_CTRL_STAT);
-       dap_dp_write_reg(swjdp, SSTICKYERR, DP_CTRL_STAT);
-       dap_dp_read_reg(swjdp, &dummy, DP_CTRL_STAT);
+
+       retval = dap_queue_dp_read(swjdp, DP_CTRL_STAT, &dummy);
+       if (retval != ERROR_OK)
+               return retval;
+
+       retval = dap_queue_dp_write(swjdp, DP_CTRL_STAT, SSTICKYERR);
+       if (retval != ERROR_OK)
+               return retval;
+
+       retval = dap_queue_dp_read(swjdp, DP_CTRL_STAT, &dummy);
+       if (retval != ERROR_OK)
+               return retval;
 
        swjdp->dp_ctrl_stat = CDBGPWRUPREQ | CSYSPWRUPREQ;
+       retval = dap_queue_dp_write(swjdp, DP_CTRL_STAT, swjdp->dp_ctrl_stat);
+       if (retval != ERROR_OK)
+               return retval;
 
-       dap_dp_write_reg(swjdp, swjdp->dp_ctrl_stat, DP_CTRL_STAT);
-       dap_dp_read_reg(swjdp, &ctrlstat, DP_CTRL_STAT);
-       if ((retval = jtag_execute_queue()) != ERROR_OK)
+       retval = dap_queue_dp_read(swjdp, DP_CTRL_STAT, &ctrlstat);
+       if (retval != ERROR_OK)
+               return retval;
+       if ((retval = dap_run(swjdp)) != ERROR_OK)
                return retval;
 
        /* Check that we have debug power domains activated */
        while (!(ctrlstat & CDBGPWRUPACK) && (cnt++ < 10))
        {
-               LOG_DEBUG("swjdp: wait CDBGPWRUPACK");
-               dap_dp_read_reg(swjdp, &ctrlstat, DP_CTRL_STAT);
-               if ((retval = jtag_execute_queue()) != ERROR_OK)
+               LOG_DEBUG("DAP: wait CDBGPWRUPACK");
+               retval = dap_queue_dp_read(swjdp, DP_CTRL_STAT, &ctrlstat);
+               if (retval != ERROR_OK)
+                       return retval;
+               if ((retval = dap_run(swjdp)) != ERROR_OK)
                        return retval;
                alive_sleep(10);
        }
 
        while (!(ctrlstat & CSYSPWRUPACK) && (cnt++ < 10))
        {
-               LOG_DEBUG("swjdp: wait CSYSPWRUPACK");
-               dap_dp_read_reg(swjdp, &ctrlstat, DP_CTRL_STAT);
-               if ((retval = jtag_execute_queue()) != ERROR_OK)
+               LOG_DEBUG("DAP: wait CSYSPWRUPACK");
+               retval = dap_queue_dp_read(swjdp, DP_CTRL_STAT, &ctrlstat);
+               if (retval != ERROR_OK)
+                       return retval;
+               if ((retval = dap_run(swjdp)) != ERROR_OK)
                        return retval;
                alive_sleep(10);
        }
 
-       dap_dp_read_reg(swjdp, &dummy, DP_CTRL_STAT);
+       retval = dap_queue_dp_read(swjdp, DP_CTRL_STAT, &dummy);
+       if (retval != ERROR_OK)
+               return retval;
        /* With debug power on we can activate OVERRUN checking */
        swjdp->dp_ctrl_stat = CDBGPWRUPREQ | CSYSPWRUPREQ | CORUNDETECT;
-       dap_dp_write_reg(swjdp, swjdp->dp_ctrl_stat, DP_CTRL_STAT);
-       dap_dp_read_reg(swjdp, &dummy, DP_CTRL_STAT);
+       retval = dap_queue_dp_write(swjdp, DP_CTRL_STAT, swjdp->dp_ctrl_stat);
+       if (retval != ERROR_OK)
+               return retval;
+       retval = dap_queue_dp_read(swjdp, DP_CTRL_STAT, &dummy);
+       if (retval != ERROR_OK)
+               return retval;
 
        /*
         * REVISIT this isn't actually *initializing* anything in an AP,
@@ -1121,10 +1324,12 @@ int ahbap_debugport_init(struct swjdp_common *swjdp)
         * Should it?  If the ROM address is valid, is this the right
         * place to scan the table and do any topology detection?
         */
-       dap_ap_read_reg_u32(swjdp, AP_REG_IDR, &idreg);
-       dap_ap_read_reg_u32(swjdp, AP_REG_BASE, &romaddr);
+       retval = dap_queue_ap_read(swjdp, AP_REG_IDR, &idreg);
+       retval = dap_queue_ap_read(swjdp, AP_REG_BASE, &romaddr);
 
-       LOG_DEBUG("AHB-AP ID Register 0x%" PRIx32 ", Debug ROM Address 0x%" PRIx32 "", idreg, romaddr);
+       LOG_DEBUG("MEM-AP #%d ID Register 0x%" PRIx32
+               ", Debug ROM Address 0x%" PRIx32,
+               swjdp->apsel, idreg, romaddr);
 
        return ERROR_OK;
 }
@@ -1147,19 +1352,27 @@ is_dap_cid_ok(uint32_t cid3, uint32_t cid2, uint32_t cid1, uint32_t cid0)
                        && ((cid1 & 0x0f) == 0) && cid0 == 0x0d;
 }
 
-int dap_info_command(struct command_context *cmd_ctx, struct swjdp_common *swjdp, int apsel)
+int dap_info_command(struct command_context *cmd_ctx,
+               struct swjdp_common *swjdp, int apsel)
 {
-
+       int retval;
        uint32_t dbgbase, apid;
        int romtable_present = 0;
        uint8_t mem_ap;
        uint32_t apselold;
 
+       /* AP address is in bits 31:24 of DP_SELECT */
+       if (apsel >= 256)
+               return ERROR_INVALID_ARGUMENTS;
+
        apselold = swjdp->apsel;
        dap_ap_select(swjdp, apsel);
-       dap_ap_read_reg_u32(swjdp, AP_REG_BASE, &dbgbase);
-       dap_ap_read_reg_u32(swjdp, AP_REG_IDR, &apid);
-       swjdp_transaction_endcheck(swjdp);
+       retval = dap_queue_ap_read(swjdp, AP_REG_BASE, &dbgbase);
+       retval = dap_queue_ap_read(swjdp, AP_REG_IDR, &apid);
+       retval = dap_run(swjdp);
+       if (retval != ERROR_OK)
+               return retval;
+
        /* Now we read ROM table ID registers, ref. ARM IHI 0029B sec  */
        mem_ap = ((apid&0x10000) && ((apid&0x0F) != 0));
        command_print(cmd_ctx, "AP ID register 0x%8.8" PRIx32, apid);
@@ -1211,7 +1424,10 @@ int dap_info_command(struct command_context *cmd_ctx, struct swjdp_common *swjdp
                mem_ap_read_u32(swjdp, (dbgbase&0xFFFFF000) | 0xFF8, &cid2);
                mem_ap_read_u32(swjdp, (dbgbase&0xFFFFF000) | 0xFFC, &cid3);
                mem_ap_read_u32(swjdp, (dbgbase&0xFFFFF000) | 0xFCC, &memtype);
-               swjdp_transaction_endcheck(swjdp);
+               retval = dap_run(swjdp);
+               if (retval != ERROR_OK)
+                       return retval;
+
                if (!is_dap_cid_ok(cid3, cid2, cid1, cid0))
                        command_print(cmd_ctx, "\tCID3 0x%2.2" PRIx32
                                        ", CID2 0x%2.2" PRIx32
@@ -1428,10 +1644,6 @@ int dap_info_command(struct command_context *cmd_ctx, struct swjdp_common *swjdp
                                        type = "TI DAPCTL";
                                        full = "";
                                        break;
-                               case 0x4e0:
-                                       type = "Cortex-M3 ETM";
-                                       full = "(Embedded Trace)";
-                                       break;
                                case 0x906:
                                        type = "Coresight CTI";
                                        full = "(Cross Trigger)";
@@ -1464,6 +1676,10 @@ int dap_info_command(struct command_context *cmd_ctx, struct swjdp_common *swjdp
                                        type = "Cortex-M3 TPIU";
                                        full = "(Trace Port Interface Unit)";
                                        break;
+                               case 0x924:
+                                       type = "Cortex-M3 ETM";
+                                       full = "(Embedded Trace)";
+                                       break;
                                case 0xc08:
                                        type = "Cortex-A8 Debug";
                                        full = "(Debug Unit)";
@@ -1507,6 +1723,9 @@ DAP_COMMAND_HANDLER(dap_baseaddr_command)
                break;
        case 1:
                COMMAND_PARSE_NUMBER(u32, CMD_ARGV[0], apsel);
+               /* AP address is in bits 31:24 of DP_SELECT */
+               if (apsel >= 256)
+                       return ERROR_INVALID_ARGUMENTS;
                break;
        default:
                return ERROR_COMMAND_SYNTAX_ERROR;
@@ -1515,8 +1734,16 @@ DAP_COMMAND_HANDLER(dap_baseaddr_command)
        if (apselsave != apsel)
                dap_ap_select(swjdp, apsel);
 
-       dap_ap_read_reg_u32(swjdp, AP_REG_BASE, &baseaddr);
-       retval = swjdp_transaction_endcheck(swjdp);
+       /* NOTE:  assumes we're talking to a MEM-AP, which
+        * has a base address.  There are other kinds of AP,
+        * though they're not common for now.  This should
+        * use the ID register to verify it's a MEM-AP.
+        */
+       retval = dap_queue_ap_read(swjdp, AP_REG_BASE, &baseaddr);
+       retval = dap_run(swjdp);
+       if (retval != ERROR_OK)
+               return retval;
+
        command_print(CMD_CTX, "0x%8.8" PRIx32, baseaddr);
 
        if (apselsave != apsel)
@@ -1558,14 +1785,20 @@ DAP_COMMAND_HANDLER(dap_apsel_command)
                break;
        case 1:
                COMMAND_PARSE_NUMBER(u32, CMD_ARGV[0], apsel);
+               /* AP address is in bits 31:24 of DP_SELECT */
+               if (apsel >= 256)
+                       return ERROR_INVALID_ARGUMENTS;
                break;
        default:
                return ERROR_COMMAND_SYNTAX_ERROR;
        }
 
        dap_ap_select(swjdp, apsel);
-       dap_ap_read_reg_u32(swjdp, AP_REG_IDR, &apid);
-       retval = swjdp_transaction_endcheck(swjdp);
+       retval = dap_queue_ap_read(swjdp, AP_REG_IDR, &apid);
+       retval = dap_run(swjdp);
+       if (retval != ERROR_OK)
+               return retval;
+
        command_print(CMD_CTX, "ap %" PRIi32 " selected, identification register 0x%8.8" PRIx32,
                        apsel, apid);
 
@@ -1584,6 +1817,9 @@ DAP_COMMAND_HANDLER(dap_apid_command)
                break;
        case 1:
                COMMAND_PARSE_NUMBER(u32, CMD_ARGV[0], apsel);
+               /* AP address is in bits 31:24 of DP_SELECT */
+               if (apsel >= 256)
+                       return ERROR_INVALID_ARGUMENTS;
                break;
        default:
                return ERROR_COMMAND_SYNTAX_ERROR;
@@ -1592,11 +1828,127 @@ DAP_COMMAND_HANDLER(dap_apid_command)
        if (apselsave != apsel)
                dap_ap_select(swjdp, apsel);
 
-       dap_ap_read_reg_u32(swjdp, AP_REG_IDR, &apid);
-       retval = swjdp_transaction_endcheck(swjdp);
+       retval = dap_queue_ap_read(swjdp, AP_REG_IDR, &apid);
+       retval = dap_run(swjdp);
+       if (retval != ERROR_OK)
+               return retval;
+
        command_print(CMD_CTX, "0x%8.8" PRIx32, apid);
        if (apselsave != apsel)
                dap_ap_select(swjdp, apselsave);
 
        return retval;
 }
+
+/*
+ * This represents the bits which must be sent out on TMS/SWDIO to
+ * switch a DAP implemented using an SWJ-DP module into SWD mode.
+ * These bits are stored (and transmitted) LSB-first.
+ *
+ * See the DAP-Lite specification, section 2.2.5 for information
+ * about making the debug link select SWD or JTAG.  (Similar info
+ * is in a few other ARM documents.)
+ */
+static const uint8_t jtag2swd_bitseq[] = {
+       /* More than 50 TCK/SWCLK cycles with TMS/SWDIO high,
+        * putting both JTAG and SWD logic into reset state.
+        */
+       0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+       /* Switching sequence enables SWD and disables JTAG
+        * NOTE: bits in the DP's IDCODE may expose the need for
+        * an old/deprecated sequence (0xb6 0xed).
+        */
+       0x9e, 0xe7,
+       /* More than 50 TCK/SWCLK cycles with TMS/SWDIO high,
+        * putting both JTAG and SWD logic into reset state.
+        */
+       0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+};
+
+/**
+ * Put the debug link into SWD mode, if the target supports it.
+ * The link's initial mode may be either JTAG (for example,
+ * with SWJ-DP after reset) or SWD.
+ *
+ * @param target Enters SWD mode (if possible).
+ *
+ * Note that targets using the JTAG-DP do not support SWD, and that
+ * some targets which could otherwise support it may have have been
+ * configured to disable SWD signaling
+ *
+ * @return ERROR_OK or else a fault code.
+ */
+int dap_to_swd(struct target *target)
+{
+       int retval;
+
+       LOG_DEBUG("Enter SWD mode");
+
+       /* REVISIT it's nasty to need to make calls to a "jtag"
+        * subsystem if the link isn't in JTAG mode...
+        */
+
+       retval =  jtag_add_tms_seq(8 * sizeof(jtag2swd_bitseq),
+                       jtag2swd_bitseq, TAP_INVALID);
+       if (retval == ERROR_OK)
+               retval = jtag_execute_queue();
+
+       /* REVISIT set up the DAP's ops vector for SWD mode. */
+
+       return retval;
+}
+
+/**
+ * This represents the bits which must be sent out on TMS/SWDIO to
+ * switch a DAP implemented using an SWJ-DP module into JTAG mode.
+ * These bits are stored (and transmitted) LSB-first.
+ *
+ * These bits are stored (and transmitted) LSB-first.
+ */
+static const uint8_t swd2jtag_bitseq[] = {
+       /* More than 50 TCK/SWCLK cycles with TMS/SWDIO high,
+        * putting both JTAG and SWD logic into reset state.
+        */
+       0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+       /* Switching equence disables SWD and enables JTAG
+        * NOTE: bits in the DP's IDCODE can expose the need for
+        * the old/deprecated sequence (0xae 0xde).
+        */
+       0x3c, 0xe7,
+       /* At least 50 TCK/SWCLK cycles with TMS/SWDIO high,
+        * putting both JTAG and SWD logic into reset state.
+        * NOTE:  some docs say "at least 5".
+        */
+       0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+};
+
+/** Put the debug link into JTAG mode, if the target supports it.
+ * The link's initial mode may be either SWD or JTAG.
+ *
+ * @param target Enters JTAG mode (if possible).
+ *
+ * Note that targets implemented with SW-DP do not support JTAG, and
+ * that some targets which could otherwise support it may have been
+ * configured to disable JTAG signaling
+ *
+ * @return ERROR_OK or else a fault code.
+ */
+int dap_to_jtag(struct target *target)
+{
+       int retval;
+
+       LOG_DEBUG("Enter JTAG mode");
+
+       /* REVISIT it's nasty to need to make calls to a "jtag"
+        * subsystem if the link isn't in JTAG mode...
+        */
+
+       retval = jtag_add_tms_seq(8 * sizeof(swd2jtag_bitseq),
+                       swd2jtag_bitseq, TAP_RESET);
+       if (retval == ERROR_OK)
+               retval = jtag_execute_queue();
+
+       /* REVISIT set up the DAP's ops vector for JTAG mode. */
+
+       return retval;
+}