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STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
Hello everyone.
I am using STM32F103VB uP with CodeSourcery GCC compiler. I have following problem. I've developed bootloader, which is loaded at the beginning of flash (0x08000000) . This bootloader uses a SD card with FAT file system, and check if some file with new firmware exists on SD card, and then loads it to flash at address 0x08008000 and call new application using such asm code:

.thumb_func
CallApplication:
// Set the vector table address to the beginning of the application.
ldr r0, =APP_VEC_TAB_OFFSET
ldr r1, =(SCB_BASE + 8)
str r0, [r1]

// Load the initial LR as it should be after the reset.
movs lr, #0xffffffff

// Load the stack pointer from the application's vector table.
ldr r0, =DEF_APP_ADDRESS
ldr r1, [r0]
msr msp, r1

// Load the initial PC from the application's vector table and branch to
// the application's entry point.
ldr r0, [r0, #4]
bx r0

Where DEF_APP_ADDRESS is 0x08000000.
When I load in such way application that is not using FreeRTOSeverything is fine. Application is loading and than running correctly, but doing the same with application based on FreeRTOS i get the HardFault Exception before calling the main in section LoopFillZerobss of startup file:
Reset_Handler:

/* Copy the data segment initializers from flash to SRAM */
movsr1, #0
bLoopCopyDataInit

CopyDataInit:
ldrr3, =_sidata
ldrr3, [r3, r1]
strr3, [r0, r1]
addsr1, r1, #4

LoopCopyDataInit:
ldrr0, =_sdata
ldrr3, =_edata
addsr2, r0, r1
cmpr2, r3
bccCopyDataInit
ldrr2, =_sbss
bLoopFillZerobss
/* Zero fill the bss segment. */
FillZerobss:
movsr3, #0
strr3, [r2], #4

LoopFillZerobss:
ldrr3, = _ebss
cmpr2, r3
bccFillZerobss
/* Call the clock system intitialization function.*/
bl SystemInit
/* Call the application's entry point.*/
blmain
bxlr
.sizeReset_Handler, .-Reset_Handler

Of course i change in the linker script line:
FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 128K
to:
FLASH (rx) : ORIGIN = 0x08008000, LENGTH = (128K - 0x8000)
and in function void vSetupHardware(void) I changed line:
NVIC_SetVectorTable( NVIC_VectTab_FLASH, 0x0 );
to:
NVIC_SetVectorTable( NVIC_VectTab_FLASH, 0x8000 );
I don't know where to find problem.

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
I forgot to add that application, which i tried to load an then execute using bootloader works perfectly in normal situation:
- in linker script is FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 128K
- in function vSetupHardware: NVIC_SetVectorTable( NVIC_VectTab_FLASH, 0x0 );

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Dave on October 28, 2010
Without having fully inspected your code, is it possible that your problem is something to do with the code that starts the scheduler loading the stack location from the interrupt table (in port.c)

void vPortStartFirstTask( void )
{
__asm volatile(
" ldr r0, =0xE000ED08 \n" /* Use the NVIC offset register to locate the stack. */
" ldr r0, [r0] \n"
" ldr r0, [r0] \n"
" msr msp, r0\n" /* Set the msp back to the start of the stack. */
" svc 0\n" /* System call to start first task. */
);
}

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
I checked this, but this function is called in vTaskStartScheduler(), but I dont even reach the main() function. Application with FreeRTOS crash with HardFault exception in startup file in this section:
/* Zero fill the bss segment. */
FillZerobss:
movs r3, #0 str r3, [r2], #4
LoopFillZerobss:
ldr r3, = _ebss cmp r2, r3
bcc FillZerobss
This section is also present in application without FreeRTOS (what is obvious), but in application without FreeRTOS everything works fine.

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
I was wrong and you were like always. The problem is in vPortStartFirstTask function. So i have to change something in this function. I will try and let you know when i solved the problem.

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
So the problem is with line:
" msr msp, r0                   \n"

When i debug code and put breakpoint on line:
" ldr r0, [r0] \n"

The value of R0 register is 0x20005000 so its correct for my processor. Maybe the the core of stm32 processor is in wrong state and cannot execute msr command. How can I check current state and how can I change it? To execute command MSR i have to be in Thread mode with privileged state?

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Dave on October 28, 2010
Can you just inspect the status register to see which mode you are in?

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
The CPSR register is uequal to 0x61000020

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Dave on October 28, 2010
...have you interpreted what that means with respect to modes and stacks. You are going to have to look it up in the manual if your debugger is not giving you the information.

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
I discover that in function vPortStartFirstTask processor is in Thread Priviliged mode and I dont know what is causing HardFault on
" msr msp, r0           \n"

Its unbelieveable.

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 28, 2010
Ok, again my fault. Initialization of MSP is done correctly. Problem is with line
"svc 0              \n"
. Its quite strange because this code works properlyy when program starts from 0x08000000. In startup file i have something like this:

.extern xPortPendSVHandler
.extern xPortSysTickHandler
.extern vPortSVCHandler
.
.
.
.
.
.
g_pfnVectors:
.word_estack
.wordReset_Handler
.wordNMI_Handler
.wordHardFault_Handler
.wordMemManage_Handler
.wordBusFault_Handler
.wordUsageFault_Handler
.word0
.word0
.word0
.word0
/*.wordSVC_Handler */
.word vPortSVCHandler
.wordDebugMon_Handler
.word0
/*.wordPendSV_Handler */
.word xPortPendSVHandler
/*.wordSysTick_Handler */
... rest of handlers ...

where

RE: STM32 + GCC + Bootloader + FreeRTOS

Posted by Sebastian K on October 29, 2010
Ok i solved problem. The problem was, that in bootloader i used Systick Timer and before calling application i didnt disable this timer. Now I disable SysTick timer in bootloader, and loaded and calles FreeRTOS application runs properly.


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