Support the Atmel STK500 and JTAGICE3 for ISP

[matthijskooijman]

This adds support for the STK500 development board.

[matthijskooijman]

I just added one more commit with support for the JTAGICE3 programmer. It doesn't actually work, due to bugs in avrdude, but since I invested the work to figure out the right commandline options etc. to use and don't want that work to get lost, I think adding it to programmers.txt already makes sense.

[cmaglie]

The configuration of stk500 looks identical to avrisp, are they the same device? May we merge them in some way to reduce the number of options?
The versions with forced firmware stk500v1 and stk500v2 are really needed?

(I always had some confusions about the amount of AVR ISP programmers available, I must admit...).

[matthijskooijman]

A lot of the ISP programmers use the same or similar protocols, so that's a bit confusing, yes. However, I'd say it is good to actually list the programmers explicitely in the menu, so it's clear to people which option they need. E.g., telling people to use AVR ISP if they have an STK500 (with firmware version 1) seems not so userfriendly. We could have an option named "AVR ISP or STK500 (firmware version 1)", but that doesn't scale well.

As for the firmware versions, just having a single stk500 entry is probably ok. However, avrdude.conf contains the following comment, which prompted me to have explicit entries too:

# This is supposed to be the "default" STK500 entry.
# Attempts to select the correct firmware version
# by probing for it.  Better use one of the entries
# below instead.

For my STK500 running v2 firmware, the default entry worked fine. If
you'd rather have a single entry, that's fine by me (we can always add
the explicit ones if we get complaints, I guess).

As for the disabled JTAGICE3 entry, I just realized that the avrdude
bugs only prevent burning the bootloader (only lock bits are broken),
programming regular sketches works. So perhaps we can just enable the
JTAGICE3 entry?

[matthijskooijman]

Ok, I just updated this pullrequest. It now only has a single STK500 entry, which should work with both firmware versions. Furthermore, I've enabled the JTAGICE3 entries, and included some comments about burn uploader not working.

Ok to merge like this?

[matthijskooijman]

I just updated the commit message of the last commit, it still said the entry was disabled (which it isn't anymore). Should be ready to merge, now.

[matthijskooijman]

I just added one more commit, that allows programming of slower parts (like brand new 328 chips).

[cmaglie]

@matthijskooijman
for JTAGICE3 it seems a bit overkill to have 3 entries just for that, I'd keep only the slow ISP mode that seems the most common for burning a bootloader, what do you think?

[matthijskooijman]

Well, one of the reasons I bought a JTAGICE3, is to get faster uploads on my Pinoccio board (uploading and verifying a 128k sketch takes over a minute through the bootloader). ISP at max speed is fast, JTAG is even faster.

So, perhaps we need submenus for programmers? :-)

[matthijskooijman]

I just rebased this PR so it applies cleanly again.

[matthijskooijman]

Superseded by #5623.