target/adi_v5_swd: fix SWD multidrop

[fw/openocd] / src / target / adi_v5_swd.c

diff --git a/src/target/adi_v5_swd.c b/src/target/adi_v5_swd.c
index 979c643e903d0a028b221bf254ccfc81e4fa868c..bd85eb217ab54cb18d86e2d0df5e4e42ef1b9d4d 100644 (file)
--- a/src/target/adi_v5_swd.c
+++ b/src/target/adi_v5_swd.c
@@ -177,6 +177,19 @@ static int swd_multidrop_select_inner(struct adiv5_dap *dap, uint32_t *dpidr_ptr
        assert(dap_is_multidrop(dap));
 
        swd_send_sequence(dap, LINE_RESET);
+       /* From ARM IHI 0074C ADIv6.0, chapter B4.3.3 "Connection and line reset
+        * sequence":
+        * - line reset sets DP_SELECT_DPBANK to zero;
+        * - read of DP_DPIDR takes the connection out of reset;
+        * - write of DP_TARGETSEL keeps the connection in reset;
+        * - other accesses return protocol error (SWDIO not driven by target).
+        *
+        * Read DP_DPIDR to get out of reset. Initialize dap->select to zero to
+        * skip the write to DP_SELECT, avoiding the protocol error. Set again
+        * dap->select to DP_SELECT_INVALID because the rest of the register is
+        * unknown after line reset.
+        */
+       dap->select = 0;
 
        retval = swd_queue_dp_write_inner(dap, DP_TARGETSEL, dap->multidrop_targetsel);
        if (retval != ERROR_OK)
@@ -196,6 +209,8 @@ static int swd_multidrop_select_inner(struct adiv5_dap *dap, uint32_t *dpidr_ptr
                        return retval;
        }
 
+       dap->select = DP_SELECT_INVALID;
+
        retval = swd_queue_dp_read_inner(dap, DP_DLPIDR, &dlpidr);
        if (retval != ERROR_OK)
                return retval;
@@ -342,6 +357,7 @@ static int swd_connect_single(struct adiv5_dap *dap)
 
                dap->switch_through_dormant = !dap->switch_through_dormant;
        } while (timeval_ms() < timeout);
+
        dap->select = DP_SELECT_INVALID;
 
        if (retval != ERROR_OK) {