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Improve the startup code on the STM32F070 #4525

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Merged
merged 3 commits into from
Jul 10, 2017
Merged

Improve the startup code on the STM32F070 #4525

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38b64ab
Improve the startup code on the STM32F070
fahhem Jun 12, 2017
53f5f66
Fix add -> adds typo
fahhem Jun 12, 2017
28e8bc0
do while -> while
fahhem Jun 12, 2017
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36 changes: 27 additions & 9 deletions ...ET_STM/TARGET_STM32F0/TARGET_NUCLEO_F070RB/device/TOOLCHAIN_GCC_ARM/startup_stm32f070xb.S
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Original file line number Diff line number Diff line change
Expand Up @@ -65,22 +65,40 @@ Reset_Handler:
mov sp, r0 /* set stack pointer */

/* Copy the data segment initializers from flash to SRAM */
movs r1, #0
// Load from _sidata -> _sdata through _edata
// _sidata has a vma = lma in flash at the end of .text
// _sdata has a lma in flash but a vma of ram, so here we move it from where
// it was loaded (lma) into where it will be accessed (vma).
// Register Schema:
// r0 = _sdata, r1 = _edata, r2 = _sidata
// r3 = index (goes from 0 -> _sdata - _edata)
// r4 = temp var for *(_sidata + r3) or (_sdata + r3)
// This is all equivalent to this C:
// int index = 0;
// extern uint32_t *_sdata, *_sidata;
// while (_sdata + index < _edata) {
// *_sdata[index] = *_sidata[index];
// index += 1;
// }
ldr r0, =_sdata
ldr r1, =_edata
ldr r2, =_sidata
movs r3, #0
b LoopCopyDataInit

CopyDataInit:
ldr r3, =_sidata
ldr r3, [r3, r1]
str r3, [r0, r1]
adds r1, r1, #4
ldr r4, [r2, r3]
str r4, [r0, r3]
adds r3, r3, #4

LoopCopyDataInit:
ldr r0, =_sdata
ldr r3, =_edata
adds r2, r0, r1
cmp r2, r3
// while (_sdata + r3 < _edata)
adds r4, r0, r3
// if (r4 < r1) branch to CopyDataInit
cmp r4, r1
bcc CopyDataInit


/* Call the clock system intitialization function.*/
bl SystemInit

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