support i2c for stm32g0x1 about embassy

[xoviat]

Generally, i2c on stm32 is something that we want to support. You need to implement the RTC and I2C traits for stm32g0xx microcontrollers.

• See the RTC implementation that works on stm32f4: https://github.com/embassy-rs/embassy/blob/master/embassy-stm32/src/rtc.rs
• See the draft I2C implementation that works on stm32f4: https://github.com/embassy-rs/embassy/pull/92/files

For the I2C implementation, you can copy this file, and then adjust it to use InterruptFuture for transmission of the address, and replace L263-L270 with DMA, like what's done in the stm32f4 PR. The F4 PR is probably almost correct, but I can't currently test it because I don't use I2C in my project. I'll probably keep is as a reference until someone needs I2C for F4.

[xoviat]

Also, join https://app.element.io/#/room/#embassy-rs:matrix.org so that we can discuss your questions in chat, and there's not so many questions in this issue.

[bobmcwhirter]

I think we have i2c now implemented for all STM32 boards, if you wouldn't mind taking a look?

If you find your target board(s) are not supported (or include too many bugs), let us know.

Thanks!

[Dirbaio]

stm32g0 is I2Cv2 which we do support. What's missing is:

• stm32g0 support itself.
• I2C slave mode (we only have master).

stm32g0 support shouldn't be hard, just enabling it here and fixing what breaks (most likely lack of RCC).

[Dirbaio]

embassy-stm32 now fully supports G0.

Tracking slave mode support in #622