core: i2c: add i2c master

[maass-hamburg]

add a i2c master similar to LiteSPI.

This has the big benefit by using crossbar, that the i2c bus can be used at the same time by drivers, that are in logic, and from the CPU.

The driver for zephyr can be found here: zephyrproject-rtos/zephyr#76554

[enjoy-digital]

Thanks @maass-hamburg, will try to review soon (but will be in holidays at the end of the week for 2 weeks).

@AndrewD might also be interested.

[AndrewD]

@maass-hamburg this does sound very interesting: do you have any examples of a gateware driver that uses this core?

We have been using the misoc i2c core for a while (recently integrated in litex): it's a step up from bitbank but small and limited, so we will look seriously at your core soon.

[maass-hamburg]

mcp9843.py.txt
@AndrewD here is one driver for the mcp9843 temperature sensor.

To add it you just have to add this code:

        from mcp9843 import MCP9843
        self.submodules.mcp9843 = mcp9843 = MCP9843()
        hvi2c.add_i2c_device(mcp9843)

hvi2c is here the submodule of LiteI2C

[AndrewD]

Thanks, that looks like quite a logical interface and the usage pattern is similar to your zephyr driver which is as I expected.

I think we will transition our usage to this core. It already exposes capabilities we were thinking about adding to the misoc i2c interface I pushed to litex recently.

Do you have any unit tests for the core you can share?

[maass-hamburg]

Do you have any unit tests for the core you can share?

Unfortunately I haven't wrote any for it yet.

[AndrewD]

I just had another look at this: the next thing that come to mind is support for IRQ so the a message can be queued without polling for completion. For example IRQ based on tx and rx fifo watermarks similar to spimmap would be one such strategy. See spi_mmap.py#L305-L315 for an implementation.

[enjoy-digital]

@maass-hamburg: sorry for the delay, just to let you know that I'll try to merge it soon, just need to think of the way we integrate it.

[maass-hamburg]

@enjoy-digital what do you think about putting it into its own repo, like LiteSPI? There we could also add some simple i2c drivers for peripherals in logic.

[enjoy-digital]

@maass-hamburg: Thanks, I was also thinking about this and this would also give your more flexibility for the development. I just created https://github.com/litex-hub/litei2c and you should have receive an invitation to maintain it. Feel free to create an initial structure close to LiteSPI and push the core to it.