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Re: [avr-chat] Mega88 bootloader?

From: Bob Paddock
Subject: Re: [avr-chat] Mega88 bootloader?
Date: Thu, 21 Jul 2005 12:13:49 -0400
User-agent: Opera M2/7.54u1 (Win32, build 3918)

I understand why it does not work now, one of those "Duh" moments,
when someone looks over your shoulder.  Of course a Relative Jump (RJMP)
is not going to jump to absolute zero.  Still don't understand
why it came out at what seems to be an arbitrary address.

Curious: what address does the reset vector jump to?

Not sure I know what you are asking there.  The Mega88 fuses
are set to jump to word address $0E00 / byte address $1C00.

At the end of the bootloader I clear IVESEL and jump to absolute
zero, now using clr r30/clr r31/ijmp , which works.

If you are asking what is at address zero it is:

00000000 <__vectors>:
   0:   40 c0           rjmp    .+128           ; 0x82
   2:   59 c0           rjmp    .+178           ; 0xb6
   4:   58 c0           rjmp    .+176           ; 0xb6

the bootloader has this at byte address 1C00:
00001c00 <__vectors>:
    1c00:       19 c0           rjmp    .+50            ; 0x1c34
    1c02:       32 c0           rjmp    .+100           ; 0x1c68
    1c04:       31 c0           rjmp    .+98            ; 0x1c68

If you go by PC = PC + k + 1 where k = 0 seems like it should effectively be a NOP, jumping to the next instruction? Not jump to some arbitrary address like -434??

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