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Re: [avr-chat] Mega88 bootloader?

From: E. Weddington
Subject: Re: [avr-chat] Mega88 bootloader?
Date: Thu, 21 Jul 2005 09:45:58 -0600
User-agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)

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.


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