mips: optimize mips32_pracc_read_u32() function

This function is highly optimized, there is not much to
improve.
Loading the base address for pracc access with the new
defined MIPS32_PRACC_BASE_ADDR saves one instruction.
The memory address is loaded in too steps. First the upper
address is loaded. The lower address is passed as an offset in
the memory load instruction.
The offset is signed, if the lower address is in the range of
0x8000 to 0xffff the offset is a negative value, and the upper
address must be incremented by 1.
Pracc accesses are now 12 instead of 14.

Change-Id: I286945b240ed5c5d5cc540780a41a8a5fa075da3
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/952
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

diff --git a/src/target/mips32_pracc.c b/src/target/mips32_pracc.c
index 0aa624c967c2d506f00f0b093a523030bbb2c5a7..72effb8e8a7381eb8582ea119a7e484e7cd04306 100644 (file)
--- a/src/target/mips32_pracc.c
+++ b/src/target/mips32_pracc.c
@@ -379,34 +379,22 @@ static int mips32_pracc_read_mem32(struct mips_ejtag *ejtag_info, uint32_t addr,
 
 static int mips32_pracc_read_u32(struct mips_ejtag *ejtag_info, uint32_t addr, uint32_t *buf)
 {
-       static const uint32_t code[] = {
-                                                                                                                       /* start: */
-               MIPS32_MTC0(15, 31, 0),                                                         /* move $15 to COP0 DeSave */
-               MIPS32_LUI(15, UPPER16(MIPS32_PRACC_STACK)),            /* $15 = MIPS32_PRACC_STACK */
-               MIPS32_ORI(15, 15, LOWER16(MIPS32_PRACC_STACK)),
-               MIPS32_SW(8, 0, 15),                                                            /* sw $8,($15) */
-
-               MIPS32_LW(8, NEG16(MIPS32_PRACC_STACK-MIPS32_PRACC_PARAM_IN), 15), /* load R8 @ param_in[0] = address */
+       uint32_t code[] = {
+                                                                                                               /* start: */
+               MIPS32_MTC0(15, 31, 0),                                         /* move $15 to COP0 DeSave */
+               MIPS32_LUI(15, PRACC_UPPER_BASE_ADDR),                          /* $15 = MIPS32_PRACC_BASE_ADDR */
+               MIPS32_SW(8, PRACC_STACK_OFFSET, 15),                           /* sw $8,PRACC_STACK_OFFSET($15) */
 
-               MIPS32_LW(8, 0, 8),                                                                     /* lw $8,0($8), Load $8 with the word @mem[$8] */
-               MIPS32_SW(8, NEG16(MIPS32_PRACC_STACK - MIPS32_PRACC_PARAM_OUT), 15), /* store R8 @ param_out[0] */
+               MIPS32_LUI(8, UPPER16((addr + 0x8000))),                        /* load  $8 with modified upper address */
+               MIPS32_LW(8, LOWER16(addr), 8),                                 /* lw $8, LOWER16(addr)($8) */
+               MIPS32_SW(8, PRACC_OUT_OFFSET, 15),                             /* sw $8,PRACC_OUT_OFFSET($15) */
 
-               MIPS32_LW(8, 0, 15),                                                            /* lw $8,($15) */
-               MIPS32_B(NEG16(9)),                                                                     /* b start */
-               MIPS32_MFC0(15, 31, 0),                                                         /* move COP0 DeSave to $15 */
+               MIPS32_LW(8, PRACC_STACK_OFFSET, 15),                           /* lw $8,PRACC_STACK_OFFSET($15) */
+               MIPS32_B(NEG16(8)),                                                     /* b start */
+               MIPS32_MFC0(15, 31, 0),                                         /* move COP0 DeSave to $15 */
        };
 
-       int retval = ERROR_OK;
-       uint32_t param_in[1];
-
-       param_in[0] = addr;
-
-       retval = mips32_pracc_exec(ejtag_info, ARRAY_SIZE(code), code,
-                       ARRAY_SIZE(param_in), param_in, 1, buf, 1);
-       if (retval != ERROR_OK)
-               return retval;
-
-       return retval;
+       return mips32_pracc_exec(ejtag_info, ARRAY_SIZE(code), code, 0, NULL, 1, buf, 1);
 }
 
 static int mips32_pracc_read_mem16(struct mips_ejtag *ejtag_info, uint32_t addr, int count, uint16_t *buf)