Re: [avrdude-dev] Modify avrdude to accept new programmer?

[Joerg Wunsch]

As Kevin Cuzner wrote:

> Now, in terms of exactly what gets sent
> when, PROGRAMMER->cmd is the important one...avrdude will give the
> commands to the programmer 4 bytes at a time along with a buffer to fill
> with whatever was received through that function.

The main reason for this is that AVRDUDE started out as a programming
tool for simple parallel-port bitbang adapters.  Thus, ISP has to be
implemented completely inside AVRDUDE, and this approach has been kept
for as long as possible.  For that reason, even the STK500 (and
STK500v2) implementation still all do the ISP manually, using the
"generic SPI" command there as much as possible.  That's basically
what the programmer's cmd method is for.

If you've got a more sophisticated programmer, you can alternatively
implement read/write functions for byte and page access yourself, and
leave the "cmd" method out.  For an example for this, have a look at
the JTAGICE (mkII and 3) implementations.  As they don't use ISP at
all, there had to be methods now that leave all the lowlevel work to
the programming hardware.

Feel free to write up all your findings into some kind of document
that can go into the AVRDUDE tree if you want.
-- 
cheers, Joerg               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/
Never trust an operating system you don't have sources for. ;-)