[avrdude-dev] avrftdi TPI support

[Hannes Weisbach]

Hello,

as of SVN r1156, avrftdi now supports TPI (and I hope I didn't break anything 
else in the process). I tested TPI support with all configurations in the 
cartesian product {Win7 x64, Ubuntu Linux 12.04.2, OS X 10.6.8} x {FT2232D, 
FT4232H} x {ATtiny10} (Thanks go to Joerg for providing the ATtiny). Bug 
reports as well as success reports are welcome.

The way that TPI works limits it's speed especially for non-H devices. avrdude 
reported about 16s for 1024 byte write and 18s for the read (4232H: 7s and 9s, 
respectively). Page read and write operations should speed up these operations 
somewhat, but TPI requires to poll a bit (NVMBSY) after each written word, so 
don't expect too much.

Cabling looks like so (monospace font!):
SCK------------TPICLK
MISO---R---+
           +---TPIDATA
MOSI---R---+

In AVR918 Atmel suggests 220Ω for R. However FTDI devices can usually sink and 
source about 8mA (don't quote me on that) so I used 1k. If 16mA I/O current is 
enabled in the FTDI you can go down to 312Ω, but I don't recommend that. 
Everything up to about 10k or so should work (at least with reduced clock rate).

Flashing with RSTDISBL fuse programmed is not (yet) supported. Unfortunately 
Atmel does not give a voltage range for HV-programming for ATtiny4/5/9/10 or a 
current on the HV-rail (Maybe Joerg can comment on that?). My current idea is 
to use a voltage doubler (Dickson charge pump) driven from TPICLK to generate 
9-ish volts and switch those to the /RESET pin, somehow. This works, because 
the ATtiny always have to be flashed from 5V.

Best regards,
Hannes