Re: [avr-chat] Mega88 bootloader?

[E. Weddington]

Bob Paddock wrote:

> I took a look at the code.  Did not really seem substantially different
> from what I had.  I solved my problem by writing SPDR twice
> after the SPM instruction.  Still seems like a part bug to me.
>
> At the end of my bootloader I have:
>
>    __asm__ __volatile__ ("rjmp 0x0000\n\t" ::);
>
>
> The code that seems to be generated is:
>
>     __asm__ __volatile__ ("rjmp 0x0000\n\t" ::);
>     1e1c:    26 cf           rjmp    .-436        ; 0x1c6a
>
> What don't I understand here?  1C6A is obviously not 0x0000.
> 1C6A is my spi_xfer() function.
>
> I'll go with your zero Z, ijmp technique that way I'm sure I will
> end up at zero.

I looked it up and a couple of issues:
1. The argument to RJMP is an *offset* to the PC, not an absolute 
address that you want to go to.
2. The argument to RJMP has a limited range of values that it can take on.

Eric