[ECOS] Redboot-GDB

[Michael Anburaj]

Hi Nick/Mark,

Let me summarize my understanding about RedbootÂ’s application invocation 
through GDB.

Psuedo code (with reference to ecos 2.0 – flow as per my code path):

cyg_start()
{
	if( ‘$’ == char on the gdb serial port)
	{
		breakpoint() /* causes a Undefined instruction exception */


Undefined exception vector handler
{
push registers into stack == _hal_registers

eventually calls __handle_exception()

return_from_exception:
	pop registers from stack /* so that it jumps to the app. */
}

__handle_exception()
{
	copy the _hal_registers into the GDB register at __cleanup_vec()

	__process_exception_vec()

	/* (my case) by this time we should have received the “c” command packet to 
start the loaded App */
	Copy the GDB registers that has the modified PC <app. Start address> into 
_hal_registers (or in other word into the exception return stack) at 
__init_vec()
}


__process_exception_vec()
{
	loop till __process_packet() returns –1 /* in my case until we see “c” 
command packet */
	{
		__process_packet()
	}
}

__process_packet()
{
	switch(gdb_command)
	{
		case ‘P’:
			(in my case) store the app start address in R15Â’s position in GDB 
registers
			return 0;

		case ‘c’:
			return –1;
	}
}


If the above is (more or less) correct, then the possibilities for the 
application code not to run after continue is issues at the gdb prompt are:
1. ARM9 var issue: Since, I used an older version of ecos source, the cache 
macros could have issues. I have synched up to the current ecos CVS 
repository & will test it on Monday.
2. The other possibly: improper SDRAM configuration, screwing the stack 
space and/or code. Which may not be the case, since the same code is running 
in a product without any issues at the same CPU speed.
3. MMU page table inconsistency.

Let me think over this. And mean while please share with me your thoughts on 
this.

Thanks a lot for the patience & support.
Cheers,
-Mike.

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