> Also the ref manual says MEM_MODE value doesnt reset to 0x00 but it does, if i set it to 0x03 after reset appears as 0x00 again
It resets to the value set by the boot procedure, e.g. if BOOT0 pin is high, it is set during boot to 0b01 to boot from the System Memory (i.e. bootloader). Thus, "normally", after reset it is set to 0b00 to boot from the "normal" FLASH.
> Once i do this, Does the linker table know that the first part of the sram should not be overwriten?
No, you should do it yourself.
There are several ways to achieve this.
As an example, in 'F031, I declare this:
#define SYSCFG_CFGR1_MEM_MODE__MAIN_FLASH 0 // x0: Main Flash memory mapped at 0x0000 0000
#define SYSCFG_CFGR1_MEM_MODE__SYSTEM_FLASH 1 // 01: System Flash memory mapped at 0x0000 0000
#define SYSCFG_CFGR1_MEM_MODE__SRAM 3 // 11: Embedded SRAM mapped at 0x0000 0000
#define VECTOR_TABLE_SIZE (USART1_IRQn /* highest supported ISR in F031 */ + 1 + 16 /* because there are "negative counted" system-exceptions and interrupts, too */)
volatile uint32_t __attribute__((section(".ram_vector,\"aw\",%nobits @"))) ram_vector[VECTOR_TABLE_SIZE];
extern volatile uint32_t g_pfnVectors[VECTOR_TABLE_SIZE];
then, as first thing in main() (*) I do this:
int main(void) {
{
uint32_t i;
RCC->APB2ENR |= RCC_APB2ENR_SYSCFGEN; // early enable to ensure clock is up and running when it comes to usage
for (i = 0; i < VECTOR_TABLE_SIZE; i++) {
ram_vector[i] = g_pfnVectors[i];
}
SYSCFG->CFGR1 = (SYSCFG->CFGR1 AND ~SYSCFG_CFGR1_MEM_MODE) OR (SYSCFG_CFGR1_MEM_MODE__SRAM * SYSCFG_CFGR1_MEM_MODE_0); // remap 0x0000000 to RAM
}
[continue with main()]
Note, that I don't use Cube's envirnoment, thus I don't have any SystemInit() or similar call in the startup code.
Symbol g_pfnVectors comes from the startup code, it's the label of the vector table, as it is located in FLASH at the beginning of the application:
startupXXXX.S:
[...]
/******************************************************************************
*
* The minimal vector table for a Cortex M0. Note that the proper constructs
* must be placed on this to ensure that it ends up at physical address
* 0x0000.0000.
*
******************************************************************************/
.section .isr_vector,"a",%progbits
.type g_pfnVectors, %object
.size g_pfnVectors, .-g_pfnVectors
g_pfnVectors:
.word _estack
.word Reset_Handler
.word NMI_Handler
.word HardFault_Handler
[etc]
And I make sure the vector table copy in RAM goes as first to the top of RAM by placing an explicit section as the first input section going into RAM, in linker script:
[here ends the code (FLASH) section]
/* redirected vector must go to top of the RAM */
.ram_vector :
{
*(.ram_vector)
} >RAM
/* used by the startup to initialize data */
_sidata = LOADADDR(.data);
/* Initialized data sections goes into RAM, load LMA copy after code */
.data :
{
. = ALIGN(4);
_sdata = .; /* create a global symbol at data start */
[etc]
JW
