Upon further investigations I found that the stack will only be de facto located in CCMRAM when I click "Debug STM Application Debug" or "Run STM Application Debug", all other times it will go back to regular RAM. I verified that using uint32_t MyStackPtr;
__asm volatile("mov %0, sp" : "=r" (MyStackPtr)); In order to move the stack to CCMRAM, I made 2 changes in sections.ld:
__stack = ORIGIN(RAM) + LENGTH(RAM);
->
__stack = ORIGIN(CCMRAM) + LENGTH(CCMRAM);
._check_stack : ALIGN(4)
{
. = . + _Minimum_Stack_Size ;
} >RAM
->
._check_stack : ALIGN(4)
{
. = . + _Minimum_Stack_Size ;
} >CCMRAM
So, apparently I'm not moving the stack correctly. However, if code is executing slower with the stack in CCMRAM, I'm not sure I want to move it. This is what my software UART code looks like:
inline static void __attribute__((optimize("O1"))) outputByte(volatile uint32_t* BSRR, uint32_t BSRRvalues[10]) {
08041040: ldr r2, [r1, #0]
08041042: ldr r3, [pc, #40] ; (0x804106c <outputByte+44>)
08041044: str r2, [r3, #24]
111 GPIOB->BSRR = BSRRvalues[1];
08041046: ldr r2, [r1, #4]
08041048: str r2, [r3, #24]
112 GPIOB->BSRR = BSRRvalues[2];
0804104a: ldr r2, [r1, #8]
0804104c: str r2, [r3, #24]
113 GPIOB->BSRR = BSRRvalues[3];
0804104e: ldr r2, [r1, #12]
08041050: str r2, [r3, #24]
114 GPIOB->BSRR = BSRRvalues[4];
08041052: ldr r2, [r1, #16]
08041054: str r2, [r3, #24]
115 GPIOB->BSRR = BSRRvalues[5];
08041056: ldr r2, [r1, #20]
08041058: str r2, [r3, #24]
116 GPIOB->BSRR = BSRRvalues[6];
0804105a: ldr r2, [r1, #24]
0804105c: str r2, [r3, #24]
117 GPIOB->BSRR = BSRRvalues[7];
0804105e: ldr r2, [r1, #28]
08041060: str r2, [r3, #24]
118 GPIOB->BSRR = BSRRvalues[8];
08041062: ldr r2, [r1, #32]
08041064: str r2, [r3, #24]
119 GPIOB->BSRR = BSRRvalues[9];
08041066: ldr r2, [r1, #36] ; 0x24
08041068: str r2, [r3, #24]
132 }
Whenever the BSRRvalues array, and hence r1, points to an address in CCMRAM, my UART runs at 2.4 MBaud. Whenever the BSRRvalues array, and hence r1, points to an address in regular RAM, my UART runs at 3 MBaud. This makes no sense to me.
