[bug #61626] jtagmkii_pdi improvements for jtag2updi use

[Joerg Wunsch]

Follow-up Comment #3, bug #61626 (project avrdude):


[comment #2 comment #2:]
> I'm not sure I follow you regarding the documentation and what you mean by
"it", sorry.

"it" = the proposed addition

> The jtag2updi project is documented on its Github repo, and the hardware
required for it to work is pretty much any AVR with at least 16k flash I
think.

But that needs to be added to either avrdude.1 or doc/avrdude.texi (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].

(DTR/RTS)

> Do you know if this is true for the actual JTAGICE mkII as well?

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).

> Will support for increased baud rates cause any backwards compatibility
issues for the jtagicemkii_pdi protocol?

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.

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