Posted on June 27, 2017 at 12:23Hi, so, I am trying to implement this situation on an STM32F407 discovery board for a test. 0) I created a simple project divided into a couple of source files. One *.c file contains a simple function that initializes the onboard LEDs. >This example works correctly. The LED initialization function is called by the main(), the LEDs are turned ON and then the programs enters an infinite loop:
int main (void)
{
Status_LEDS_Init ();
while (1)
{
}
}1) After that, I have modified the linker script, and I added a new section to the memory map, like the example:
/* Specify the memory areas */
MEMORY {
FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 512K
FW (rx) : ORIGIN = 0x08080000, LENGTH = 512K
RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 128K
MEMORY_B1 (rx) : ORIGIN = 0x60000000, LENGTH = 0K
CCMRAM (rw) : ORIGIN = 0x10000000, LENGTH = 64K
}2) I placed the section .firmware descriptor between .text and .rodata:
...
/* The program code and other data goes into FLASH */
.text :
{
. = ALIGN(4);
*(.text) /* .text sections (code) */
*(.text*) /* .text* sections (code) */
*(.glue_7) /* glue arm to thumb code */
*(.glue_7t) /* glue thumb to arm code */
*(.eh_frame)
KEEP (*(.init))
KEEP (*(.fini))
. = ALIGN(4);
_etext = .; /* define a global symbols at end of code */
} >FLASH
.firmware :
{
*(.firmware*)
} >FW
/* Constant data goes into FLASH */
.rodata :
{
...3) The project compiled correctly, so I forced the function that initializes the LEDs to be placed in .firmware section.
__attribute__((section('.firmware'))) int Status_LEDS_Init (void)
{
/*
* DESCRIPTION: This function is used to initialize the hardware that drives
* the GPIOs connected to the two status LEDs.
* PARAMETERS: See Above.
* RETURNS: Nothing.
*/
// Local GPIO structure used to setup lines using the Standard Peripheral
// Library.
GPIO_InitTypeDef lGPIO_InitStructure;
// Turn on the MCU peripheral by enabling its Clock.
RCC_AHB1PeriphClockCmd (STATUS_LEDS_RCC, ENABLE);
// Configure the output lines connected to the Status LEDs as output, LOW
// level as default.
lGPIO_InitStructure.GPIO_Pin = STATUS_LED1 | STATUS_LED2 | STATUS_LED3 | STATUS_LED4;
lGPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
lGPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
lGPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
lGPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_DOWN;
GPIO_Init (STATUS_LEDS_PERIPHERAL, &lGPIO_InitStructure);
// Put LEDs line HIGH.
STATUS_LEDS_PERIPHERAL->ODR |= (STATUS_LED1 | STATUS_LED2 | STATUS_LED3 | STATUS_LED4);
return 1;
} // End Status_LEDS_Init.4) The project compiles, and from the debugger, I can see clearly that this function is placed correctly at 0x0808000, where the .firmware section starts. Of course, the program works perfectly. Now I know that this function is placed at the absolute address 0x08080000. 5) I tried to change the way of calling the function, by using this address:
...
typedef int (*func)(void);
int main (void)
{
((func)0x08080000) ();
while (1)
{
}
}6) The code is compiled perfectlòy but the program goes to 'Hardfault error'. So I checked the ASM code, tried to trace the execution step by step, and I wasn't able to understand where the problem is since the program jumps to that location in both cases, but when the function is called with the symbol name it works. When it's called with the address location it doesn't work.
7) I tried to put both calls in the main to see the differences in the ASM:
typedef int (*func)(void);
int main (void)
{
Status_LEDS_Init ();
((func)0x08080000) ();
while (1)
{
}
}7) Compiled and got this ASM:
0800f0c4: ldr r3, [pc, #8] ; (0x800f0d0 <main+16>)
0800f0c6: blx r3
0800f0c8: ldr r3, [pc, #8] ; (0x800f0d4 <main+20>)
0800f0ca: blx r3
0800f0cc: b.n 0x800f0cc <main+12>
0800f0ce: nop 😎 The two calls are absolutely the same, but the first works, the second, after jumping the PC to 0x0808000, goes to Hardfault. This is the end of the story
:(
I am going crazy. Do you have an idea of what this problem is caused by?
