How one program can download and run another.

My last post was slightly wrong - it seems that once I added a change to an LED on the board I noticed that things did sometimes work - I just wasn't getting any printf output. Once I realised that it did sometimes run OK I was able to come up with something which seems to work all the time:

The bootloader now disables all interrupts (and does not bother to keep the returned context) before the jump to the downloaded program:

// Disable ALL Interrupts

alt_irq_disable_all();

// Start downloadable

asm("MOVIA %0, %1" : "=r" (Jump) : "i" DOWNLOADABLE_START_ADDRESS));

asm("JMP %0" : : "r" (Jump));

The alt_main function now starts like this:

/* Copy exception code from 0x000FFE00 to 0x20. */

unsigned char *src = (unsigned char *) 0x000FFE00;

unsigned char *dest = (unsigned char *) 0x00000020;

unsigned char *end = (unsigned char *) 0x000001C8;

int context = alt_irq_disable_all();

while (dest != end)

{

*dest = *src;

dest++;

src++;

}

alt_dcache_flush_all();

alt_icache_flush_all();

alt_irq_enable_all(context);

Note that I've removed the redundant dereference('*') from *dest++ and *src++.

I still need to wait for or clear pending interrupts in the bootloader program, at the moment I allow any printf output to finish by putting in a call to usleep. Without this it seems to still work but not all the printf output is seen.