Writing bytes to internal flash memory blocks all interrupts on the STM32L0 despite moving the vector table and ISR functions to RAM
The Context
I have a embedded system running on an STM32L053 processor that needs to process STM32 hardware timer interrupts regularly and cannot be disabled. These top-priority interrupts cannot be prevented because it could cause a failure in the whole system. I also need to process user inputs that can cause writes to NVM (non-volatile memory) at random times to save settings while processing timer interrupts concurrently. I am using IAR compiler.
The problem
During the flash writes that can occur randomly, it blocks CPU execution as well as all interrupts for about 6ms. This is a problem because the processing of hardware timer interrupts cannot be prevented or it can cause a failure of the entire system.
The potential solution
After some research, I found this document on ST's website that explains exactly how to manage this problem. From what I understand in this document, the list of things to do to prevent the blocking of interrupts are the following:
- Initiating the flash writes from RAM.
- Interrupt handler code must be placed in RAM
- Abstain from using constants that are placed in program Flash memory
- Data EEPROM cannot be read while being written
- Vector table relocated in RAM
- Vector table address must be written in the System Control Block register VTOR.
- Check that the vectors in the table needed during data EEPROM write access period are pointing to RAM
Vector table relocation
void SystemInit (void)
{
// (...)
/* Configure the Vector Table location add offset address ------------------*/
#ifdef VECT_TAB_SRAM
/* Vector Table Relocation in Internal SRAM */
#pragma section = ".intvec_RAM"
SCB->VTOR = (uint32_t)__section_begin(".intvec_RAM");
#else
SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH */
#endif
}Linker Script:
Linker Script
/*###ICF### Section handled by ICF editor, don't touch! ****/
/*-Editor annotation file-*/
/* IcfEditorFile="$TOOLKIT_DIR$\config\ide\IcfEditor\cortex_v1_0.xml" */
/*-Specials-*/
define symbol __ICFEDIT_intvec_start__ = 0x08000000;
/*-Memory Regions-*/
define symbol __ICFEDIT_region_ROM_start__ = 0x08000000 ;
define symbol __ICFEDIT_region_ROM_end__ = 0x0800FFFF;
define symbol __ICFEDIT_region_RAM_start__ = 0x200000EC;
define symbol __ICFEDIT_region_RAM_end__ = 0x20001FFF;
/*-Sizes-*/
define symbol __ICFEDIT_size_cstack__ = 0x400;
define symbol __ICFEDIT_size_heap__ = 0x200;
/**** End of ICF editor section. ###ICF###*/
define symbol __RAM_intvec_start = 0x20000000;
define memory mem with size = 4G;
define region ROM_region = mem:[from __ICFEDIT_region_ROM_start__ to __ICFEDIT_region_ROM_end__];
define region RAM_region = mem:[from __ICFEDIT_region_RAM_start__ to __ICFEDIT_region_RAM_end__];
define block CSTACK with alignment = 8, size = __ICFEDIT_size_cstack__ { };
define block HEAP with alignment = 8, size = __ICFEDIT_size_heap__ { };
initialize by copy { readwrite };
initialize by copy { section .intvec_RAM };
do not initialize { section .noinit };
place at address mem:__ICFEDIT_intvec_start__ { readonly section .intvec };
place at address mem: __RAM_intvec_start { section .intvec_RAM };
place in ROM_region { readonly };
place in RAM_region { readwrite,
block CSTACK, block HEAP };Startup Script:
I have two startup scripts added to my project, one with the original vector table (in flash) that has all the handlers except forReset_Handler replaced with Empty_Handler and the other that has the handlers placed in RAM.
The ISR Code:
__ramfunc void TIM22_IRQHandler(void)
{
if(LL_TIM_IsActiveFlag_TRIG(TIM22) == 1)
{
LL_TIM_ClearFlag_TRIG(TIM22);
}
if(LL_TIM_IsActiveFlag_CC2(TIM22) == 1)
{
LL_TIM_ClearFlag_CC2(TIM22);
LL_TIM_ClearFlag_CC2OVR(TIM22);
}
}The Flash write blocking code
This is the piece of code that blocks all interrupts from happening for about about 6ms (the time it takes for a write to flash). It called periodically.
typedef struct
{
uint8_t uniqueNumber; // 1 byte
} Eeprom_t;
__ramfunc static void SaveStuffToFlash(void)
{
static uint8_t _numberToStore = 1;
_eepromData.uniqueNumber = _numberToStore;
while(__HAL_FLASH_GET_FLAG(FLASH_FLAG_BSY) == 1)
{
// wait for flag to go to zero.
};
_numberToStore++;
}The persistent problem
I don't know why, but the interruptions are still getting blocked when the SaveStuffToFlash() function is called. I don't have all the code in RAM, only the code that does the save to the internal flash. I followed all the directions in the application note and it seems to still block interrupts. I have run out of ideas and means to debug this.
