Support of Atmega8

[xfmoulet]

Hi, I would like to use the Atmega8 chip, which do not seem to be supported by now.
I don't know enough of the avh-hal system to implement it myself (but I could try with some help)

[stappersg]

On Wed, Nov 09, 2022 at 03:14:53AM -0800, Xavier-Frédéric Moulet wrote: ... but I could try with some help

#362

[Rahix]

@stappersg, #362 adds a board to arduino-hal, that's not what the issue poster needs to do. They need to add a new MCU to atmega-hal which works differently.

@xfmoulet, as a reference for adding a new MCU, maybe PR #306 is a better candidate. You need to mostly follow what happens there. You can open a draft PR once you got the bare basics working and need help with some more specific things (e.g. ADC, PWM, ...). Just let me know when you get stuck anywhere.

[xfmoulet]

I have an issue (so closing this PR for the moment) : adps() method prescaler_2 does not exist, only bit definitions ...
I try to find a way to temporarily disable the ADC device for the moment (I guess the other possibility would be to enable is automated extraction in avr-device ?)

[Rutherther]

I think I have done the needed patches in avr-device for this. See Rahix/avr-device#112
I've also tried to implement ATmega8 to avr-hal, see the relevant commit here: Rutherther@67fb8b1

There were some problems with that as the rest of the ATmega's are different to ATmega8 (EEPROM does not use erase mode, ADC does not have DIRD). I have added macros to avr-generic-hal specific to ATmega8 (in eeprom.rs and adc.rs), does that make sense? I suppose there are other microcontrollers that will work the same way so it could be useful in the future. What do you think, @Rahix? Do you have any better idea?

Also name of the register for wdt is different, as a hotfix I added cfg feature to avr-generic-hal wdt.rs. What is the correct way to handle this? Should I add parameters to the macro that will access the correct register? (wdtcsr for other megas, wdtcsr for ATmega8)

I have not yet tested anything except EEPROM, so I won't make a PR yet, but you can expect it in a week.

[Rutherther]

Another thing is that ATMega8 does not support watchtog at 4000 ms and 8000 ms timeouts, what would the correct way to handle that be? main...Rutherther:avr-hal:main#diff-6697f39027bdefb403a8c88673c635515ca9737eb92bf78393b97feffc9b6725R39

Also the rest of the other timeouts areno not exaclty the same either for ATmega8:

(instead of 125 ms it's 130 ms, and it gets worse the higher we go)

[Rahix]

As we now have two PRs for ATmega8 open here, #368 by @xfmoulet and #384 by @Rutherther, how shall we proceed? Should we just drop one or is there work to be merged from both?

[xfmoulet]

I did not have enough time to pursue patching the generator, and I think @Rutherther went further than I did with its implementation, I can retire mine if you agree with it.

[Rahix]

Alright, let's go that route. Thanks anyway for initially starting the work on this topic!