[bug #61626] jtagmkii_pdi improvements for jtag2updi use

[mcudude]

Follow-up Comment #4, bug #61626 (project avrdude):


> But that needs to be added to either avrdude.1 or doc/avrdude.taxi (I'm
willing to copy it over to the other of both documents), and maybe the URL
also should be documented in avrdude.conf[.in].

Would be great if the essence could be scissored out and added to the docs. A
link to the repo is probably also a good idea.


> AFAICT the original JTAGICE mkII doesn't use DTR/RTS, and it is mostly
talked with these days through its USB connector (which is not going to a
USB-serial chip inside but to an old NXP parallel chip). 

Ah, the PDIUSBD12 chip! Haven't really seen it in anything else than in AVR
programming hardware; wonder why... So if I understand you correctly, pulling
DTR/RTS low before "hello" and releasing after "goodbye" shouldn't cause any
harm/compatibility issues with existing hardware. Excellent!


> When being talked to through the serial connection, the JTAGICE mkII behaves
in a very specific way: it always uses 19200 Bd to attach to, but then
switches to 115200 Bd on the fly once the connection has been established.
That's why it is also necessary to correctly say "good-bye" to it, as by that,
it reverts to 19200 Bd. Also, that "hello" / "good-bye" sequence is used to
deactivate the unused of the two connectors while being active (RS232 vs.
USB). 
Thus, the jtagmkII.c code hardcodes the 19200 Bd default speed, while the
baudrate configured on the commandline or in avrdude.conf is only used for the
active connection.

But there is nothing in the protocol that limits the speed to a maximum baud
rate of 115200? Heck, could we theoretically use 230400, 250000, 460800 or
500000,  921600 or even 1M if Avrdude supported it (in function
jtagmkII_get_baud())?

Quick last question. I was very pleased to see some activity here. After all,
I use Avrdude alot, and I love the fact that SO many programmers are
supported.
Is the current plan to apply patches and fix critical bugs and call it a day
(and that's totally OK), or will further development continue in the future,
perhaps driven by bug reports, feature requests and user-applied patches?
Regardless, I'm very thankful for all your contributions over the the years,
resulting in a tool that's used by the entire AVR community to this very day.

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