[avrdude-dev] [patch #6530] Arduino improvement

[Joerg Wunsch]

Follow-up Comment #2, patch #6530 (project avrdude):

Sorry, this patch is IMHO completely broken.  Did you ever try
this on a real STK500 with a V1 firmware?

According to appnote AVR068, CMD_READ_SIGNATURE_ISP takes
6 bytes: Command ID, RetAddr, cmd1, cmd2, cmd3, and cmd4.
It reads exactly *one* signature byte, which must be encoded
into the lower two bits of cmd3, so the command must be
issued three times, to get all three signature bytes.
Essentially, it's not all that different than using spi_multi
directly (which is what avr_read() falls back to if there's
no read_sig_bytes() method).

So please resubmit the patch in a way that has been tested
with an original Atmel STK500 running V1 firmware.

Also, backwards compatibility issues are to be considered.
AVRDUDE has been around using the method as currently imple-
mented for more than 6 years.  As Atmel abandoned V1 many
years ago, it can be assumed that there are enough implemen-
tations (like bootloaders) that can be found in the wild
which rely on AVRDUDE's current behaviour.  For that reason,
I'd like to have the Arduino-compliant functionality
explicitly enabled (like, through a -x extension option)
rather than defaulting to it.

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