Problem with manually allocating memory address for a pointer-CodePudding

I am trying to work with flash memory on MPC5748G - a microcontroller from NXP running FreeRTOS 10.0.1, and I get some behaviour that I can't understand.

I am allocating memory manually, and the assignment seems not to work. However, I can reach the value at the address when using 'printf' - but only from the same function. (I'm using the copy of a pointer, to make sure that some sore of compiler optimisation doesn't take place)

void vFlashTask(void* pvParameters){
   vTaskDelay(1000);
   FLASH_DRV_Init();
   uint32_t* val_ptr; 
   uint32_t* val_ptr_cpy;
   val_ptr = (uint32_t *)0xFB8000;
   val_ptr_cpy = val_ptr;
   
   *val_ptr = 444;

   DBGPRINTF("Task| value at xFB8000:%d", *val_ptr_cpy);
   
   getValTest();
   vTaskDelay(1500);
   vTaskDelete(NULL);
}

void getValTest(){
   uint32_t* val_ptr;
   val_ptr =(uint32_t *)0xfb8000;
   DBGPRINTF("getValTest| value at xFB8000:%d", *val_ptr);
}

Gives back (in UART Terminal):

   [../include/flash.c:26]: Task| value at xFB8000:444
   [../include/flash.c:37]: getValTest| value at xFB8000:-1

I am attaching also the screenshot from the debugger, which clearly shows that however memory at the xFB8000 is uninitialized (it has the value of 0xffffffff), but still, the printf function manages to print the correct value(?).

My DBGPRINTF macro:

#define DBGPRINTF(f, ...)           dbgPrintf("[%s:%d]: " f "\n", __FILE__, __LINE__, __VA_ARGS__)

void dbgPrintf(const char *format, ...){
    va_list args;
    va_start(args, format);
    int len = vsnprintf((char*) uart_buffer, UART_BUFFER_SIZE - 1, format,  args);
    UART_SendDataBlocking(&uart_pal1_instance, (const char *)uart_buffer, len, UART_TIMEOUT);
    va_end(args);
 }

I would really appreciate any help or suggestions.

My compiler flags:

\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/rtos/FreeRTOS_PA/Source/portable/GCC/PowerPC" -I"C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/middleware/tcpip/tcpip_stack/ports/OS" -I"C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/middleware/tcpip/tcpip_stack/ports/platform/generic/gcc/setting" -I"C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/middleware/tcpip/wolfssl/wolfssl" -I"C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/middleware/tcpip/wolfssl" -I"C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/rtos/FreeRTOS_PA/Source" -I"C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/platform/pal/inc" -I"C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/software/S32_SDK_S32PA_RTM_3.0.3/platform/drivers/src/flash_c55" -O1 -g3 -Wall -c -fmessage-length=0 -msdata=eabi -mlra -funsigned-bitfields -ffunction-sections -fdata-sections -fno-common -Wno-address -mcpu=e200z4 -specs=nosys.specs -mbig -mvle -mregnames -mhard-float --sysroot="C:\NXP\S32DS_Power_v2.1\eclipse\../S32DS/build_tools/powerpc-eabivle-4_9/powerpc-eabivle/newlib"

CodePudding user response：

The problem was writing to FLASH memory - it hasn't been correctly initialized.

The proper way to write to flash on MPC5748g using the SDK 3.0.3 is following:

save flash controller cache
initialise flash
check and protect UT block
unblock an address space
erase a block in this space
check if the space block is blank
program the block
verify if the block is programmed correctly
check sum of the programmed data
restore flash controller cache

The strange behaviour of printf and pointer was due to compiler optimization. After changing the compiler flags to -O0 (no optimization), the error was consistent.

The same consistent error can be achieved when marking the pointers as 'volatile'.