DFU: set stack pointer before starting main app

The stack size is fixed. The linker script puts the stack section
after the bss section. The initial stack pointer is not at the
end of the RAM (as often seen).
Thus the initial stack pointer address of the main application
is different than the one from DFU. When starting the main
application the stack pointer needs to be set to the new value.
If this is not done the main application stack may overwrite the
data in bss, even without exceeding the fixed stack size.

Change-Id: Ie354d603fe302d3d5bdfa9c31575411de722323b

1 files changed, 5 insertions, 1 deletions

diff --git a/firmware/libboard/common/source/board_cstartup_gnu.c b/firmware/libboard/common/source/board_cstartup_gnu.c
index 15c70dd..4b561ec 100644
--- a/firmware/libboard/common/source/board_cstartup_gnu.c
+++ b/firmware/libboard/common/source/board_cstartup_gnu.c
@@ -133,7 +133,11 @@ static void BootIntoApp(void)
 	void (*appReset)(void);

 

 	pSrc = (unsigned int *) ((unsigned char *)IFLASH_ADDR + BOARD_DFU_BOOT_SIZE);

-	SCB->VTOR = ((unsigned int)(pSrc)) | (0x0 << 7);

+	/* set vector table to application vector table (store at the beginning of the application) */

+	SCB->VTOR = (unsigned int)(pSrc);

+	/* set stack pointer to address provided in the beginning of the application (loaded into a register first) */

+	__asm__ volatile ("MSR msp,%0" : :"r"(*pSrc));

+	/* start application (by jumping to the reset function which address is stored as second entry of the vector table) */

 	appReset = (void(*)(void))pSrc[1];

 

 	g_dfu->state = DFU_STATE_appIDLE;