Add comments and tiny improvements to STM32 flash loader algorithm

[openocd] / contrib / loaders / flash / stm32x.s

diff --git a/contrib/loaders/flash/stm32x.s b/contrib/loaders/flash/stm32x.s
index dcf2b83ccc781e74b2a85bc0b454a7e85744513e..6cf9f5791cbb6dcf6bfba476830e4493af9cfc0e 100644 (file)
--- a/contrib/loaders/flash/stm32x.s
+++ b/contrib/loaders/flash/stm32x.s
@@ -19,7 +19,10 @@
  ***************************************************************************/
 
        .text
-       .arm
+       .syntax unified
+       .thumb
+       .thumb_func
+       .global write
 
 /*
        r0 - source address
@@ -27,26 +30,27 @@
        r2 - count (halfword-16bit)
        r3 - result
        r4 - temp
-       r5 - temp
 */
 
+#define STM32_FLASH_CR_OFFSET  0x10                    /* offset of CR register in FLASH struct */
+#define STM32_FLASH_SR_OFFSET  0x0c                    /* offset of CR register in FLASH struct */
+
 write:
-       ldr             r4, STM32_FLASH_CR
-       ldr             r5, STM32_FLASH_SR
-       mov             r3, #1
-       str             r3, [r4, #0]
-       ldrh    r3, [r0], #2
-       strh    r3, [r1], #2
+       ldr             r4, STM32_FLASH_BASE
+write_half_word:
+       movs    r3, #0x01
+       str             r3, [r4, #STM32_FLASH_CR_OFFSET]        /* PG (bit0) == 1 => flash programming enabled */
+       ldrh    r3, [r0], #0x02                                         /* read one half-word from src, increment ptr */
+       strh    r3, [r1], #0x02                                         /* write one half-word from src, increment ptr */
 busy:
-       ldr     r3, [r5, #0]
-       tst     r3, #0x01
-       beq     busy
-       tst             r3, #0x14
-       bne             exit
-       subs    r2, r2, #1
-       bne             write
+       ldr     r3, [r4, #STM32_FLASH_SR_OFFSET]
+       tst     r3, #0x01                                                       /* BSY (bit0) == 1 => operation in progress */
+       beq     busy                                                            /* wait more... */
+       tst             r3, #0x14                                                       /* PGERR (bit2) == 1 or WRPRTERR (bit4) == 1 => error */
+       bne             exit                                                            /* fail... */
+       subs    r2, r2, #0x01                                           /* decrement counter */
+       bne             write_half_word                                         /* write next half-word if anything left */
 exit:
-       bkpt    #0
+       bkpt    #0x00
 
-STM32_FLASH_CR: .word 0x40022010
-STM32_FLASH_SR:        .word 0x4002200C
+STM32_FLASH_BASE: .word 0x40022000                             /* base address of FLASH struct */