Posted on February 20, 2018 at 00:05Using Clive Oness guidance from above, I have it working now for the L496. To answer one of my questions above, the boot loader code does look after everything wrt to the USART and Systick set up. In the startup_stm32l496xx.s file, I inserted this just before the STM generated branch to main ( 'bl main') :
/* Look for boot loader signature. */
LDR R0, =0x20002000
// note different location for my system compared to example above
LDR R1, =0xDEADBEEF
LDR R2, [R0, &sharp0]
/* Invalidate */
STR R0, [R0, &sharp0]
CMP R2, R1
BEQ Reboot_Loader
LDR R0, =SystemInit
BLX R0
bl main
Reboot_Loader:
/* Boot Loader BASE */
LDR R0, =0x1FFF0000
// note different boot loader location for L496 compared to above
LDR SP, [R0, &sharp0]
// SP @ +0
LDR R0, [R0, &sharp4]
// PC @ +4
BX R0
// jump to bootloader
/* Call the application's entry point.*/
<-this generated by STM
bl main
<-this is generated by STM and could be removed now
LoopForever:
<-this is generated by STM
b LoopForever
<-this is generated by STM
And the function that starts it all:
void
bootload(
void
)
{
*((
unsigned
long
*)0x20002000) = 0xDEADBEEF;
NVIC_SystemReset();
while
(1);
// this should never happen!
}
For the L496, I will try placing the DEADBEEF signature into an area of flash that will be off limits to my update program. I will also not overwrite the code in the startupxxx.s file during an update. Once the new code has been completely written and verified, then I will clear the DEADBEEF flash location with the update program. I believe that this will keep the system in the boot load mode even if power or coms are interrupted during an update.
6 Mar 2018: Update for conversion to STM32L4R5: The stm32lr5 has a couple of changes compared to the stm32l496 that require an addition to the assembler startup file. The Syscfg register must be modified to map the bootloader to address 0x00000000:
/* Look for boot loader signature. */
LDR R0, =0x20040000
LDR R1, =0xDEADBEEF
LDR R2, [R0, &sharp0]
/* Invalidate */
STR R0, [R0, &sharp0]
CMP R2, R1
BEQ Reboot_Loader
LDR R0, =SystemInit
BLX R0
bl main
Reboot_Loader:
/* Remap bootloader code to address 0x00000000 */
LDR R0, =0x40021060
// address of the clock enable register for access to syscfg
LDR R1, =0x00000001
// only need to set bit one to 1. All others will be 0 out of reset
STR R1, [R0, &sharp0]
LDR R0, =0x40010000
// location of SYSCFG_MEMRMP
LDR R1, =0x00000001
STR R1, [R0, &sharp0]
/* Boot Loader BASE */
LDR R0, =0x00000000
LDR SP, [R0, &sharp0]
// SP @ +0
LDR R0, [R0, &sharp4]
// PC @ +4
BX R0
// jump to bootloader
/* Call the application's entry point.*/
bl main
LoopForever:
b LoopForever
