Passing info from bootloader to application
2014-08-18 by Chuck Hackett
I have an ATMega1284p based application. I have a bootloader installed. My application needs to know the reason for a start/restart (power-on, reset button, brown-out, WDT, etc.).
Before I started using the bootloader my application did this be saving the MCUSR immediately upon startup:
uint8_t mcucsr_mirror __attribute__ ((section (".noinit")));
__attribute__ ((no_instrument_function)) void Restart_ProcessRestart(void) \
__attribute__((naked)) \
__attribute__((section(".init3")));
void Restart_ProcessRestart(void)
{
mcucsr_mirror = MCUSR;
MCUSR = 0;
wdt_disable();
….
With the bootloader installed the MCUSR is getting destroyed by the bootloader so the application does not have access to it.
I have the source to the bootloader.
What is the best way to pass 1 byte of information from the bootloader to the application?
I know that I could define a common ‘mailbox’ memory location but I would like to keep the bootloader application independent.
The current ‘main’ called by the bootloader is defined as:
void (*app_start)(void) = 0x0000;
Can the ‘main’ being called by the bootloader be defined with parameters?
void (*app_start)(uint8_t MCUSR) = 0x0000;
Will this work if an application which does not care about the MCUSR defines it’s ‘main’ as ‘normal’?
void main(void);
If this is not appropriate, can I pass the value in a register?
If so, what register (as I recall GCC requires R1 to be 0)?
I assume assembly code will be required. I have not done assembly programming on the AVR so applicable assembly snippets would be appreciated.
Nope, this is not for homework – I’m 65 and way past school J
Cheers,
Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck