[avr-chat] Struggling to write usersig with avrdude on an xmega256a3

[Travis Griggs]

I'm not sure if this is a bug, known issue, or just me doing something wrong. I 
do know that avrdude and my mkII programmer program the device just fine. And 
I'm hugely grateful to the avrdude folks for making it a possibility. I'm on 
OSX (10.8) using CrossPack's latest avr package.

The command I try is

avrdude -p atxmega256a3 -P usb -c avrispmkii -e -U usersig:w:0BDE0010.hex:i

It fails at the verify step. Using the read variant of the above (which works 
fine), I can see that it somehow mashed new write with the old contents, ending 
up with something in between. So the verify fails.

Am I doing something wrong? Is this a known bug or feature lack with avrdude? I 
had seen that there was a patch for the 324 I think, to etc/avrdude.conf. I 
played with the usersig a bit:

 memory "usersig"
        size        = 0x200;
        offset      = 0x8e0400;
        page_size   = 0x100;
        readsize    = 0x100;
    ;

changing page/read size to 0x200, but it didn't make a difference.

TIA

--
Travis Griggs
"Ninety per cent of most magic merely consists of knowing one extra fact." 
-Terry Pratchett