[Uisp-dev] AVR910 protocol

[Joakim Arfvidsson]

Is anyone deeply familiar with the AVR910 implementation in uisp?


Short question (read on for background) : Is there any character I, 
from the programmer hardware, can send subsequent to a confirming reply 
of a byte written, that uisp will ignore? Or would you know where I'd 
have to mess with the source to insert that behaviour?


I made a USB AVR programmer simply by combining the AVR910 appnote 
(with its code) and a FT232BM USB chip. That USB chip buffers the data 
going to the computer and won't send it on until either the buffer is 
full (on the order of 100 bytes) or a certain timeout expires. The 
default is 16 ms, which compared to the minimum of 1 ms really means 16 
times worse performance with the latency-sensitive AVR910 protocol.

The real problem is that the mac drivers won't allow setting this 
timeout value, while the Windows ones do (there is no way to do it in 
hardware).

Since there is not even a pin "send directly" on the FT232BM chip, I'm 
seriously considering padding data up the the RX buffer size to have it 
sent immediately. So is there anything I could pad with that uisp would 
ignore? Or do you supposed I could hack the code? I'm a C programmer, 
but perhaps the architecture of AVR910 implementation would make this 
hard... you would have to be reading everything available and not just 
a byte when you expect when there is one available (the confirmation 
byte from my programmer).

Any tips appreciated!

Link to the programmer: http://www.e.kth.se/~joakimar/hardware

Joakim Arfvidsson

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