[avrdude-dev] Patch to stk500v2 to support non-USB XPROG

[Erik Walthinsen]

In developing a stk500v2 XPROG bootloader for my product, I ran into a 
problem with avrdude switching into the USB-only unframed version of the 
protocol after SIGN_ON.  It does so because of an assumption that every 
stk500v2-xprog device will be communicating over USB.  In my case I'm 
running over a serial link (and soon running that over a mutliplexed 
protocol), and the assumption is no longer correct.

I did a quick hack to the stk500v2.c code in order to make both cases 
work.  Basically it adds a struct var 'bareproto', which is used to 
decide whether to send the stk500 commands framed or unframed, rather 
than the specific programmer type.  The flag itself is set when the 
actual comms port is selected, and currently is only set if it's USB.

Being a quick hack I don't expect this patch to go anywhere itself. 
However, something like it should be put in place, since non-USB XPROG 
implementations are likely to show up (especially since I'll be 
releasing mine at some point soon...).

Likely a better way to implement it would be an avrdude.conf flag that 
would specifically set it to "framed-mode".  Along those lines it would 
be nice to have some way to define programmers by their SIGN_ON 
responses.  Since SIGN_ON is always sent in full stk500 framed mode no 
matter what, having avrdude check through the .conf for a string match 
(rather than hard-coded) and then picking up the "framed-mode" flag 
before continuing would make it easy to define new programmer types for 
bootloaders, etc.

Due to my development schedule I'm unable to do anything further on this 
at this point, but if it's still an issue when I have a bit more time, 
I'll see if I can give it a go.

Patch is attached, and I'll be filing it in the bug tracker in a couple 
minutes.

stk500v2-bareproto.diff
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