Support for MCP2221/MCP2221A

[kabili207]

What kind of new feature are you looking for?

• Hardware: MCP2221/MCP2221A - https://www.microchip.com/en-us/product/MCP2221A

These are similar to the FTDI232X chips in that they expose GPIO and I2C over USB. (They also expose UART and an ADC and DAC, but I believe those are out of scope for this periph)

Adafruit has a handy little breakout for this chip available here: https://www.adafruit.com/product/4471

Do you plan to:

• Contribute an initial driver: Not likely. I may try to port https://github.com/ardnew/mcp2221a over to this project, but I can't make any promises
• Write unit tests: I don't think unit tests would be possible without the actual hardware
• Update https://github.com/periph/cmd to use the new functionality: This would already be covered by the generic i2c commands, yeah?

[kabili207]

Additional note: there is a kernel module for this in Linux (https://github.com/torvalds/linux/blob/master/drivers/hid/hid-mcp2221.c), however it's not enabled by default in any major distro and I'd really rather not have to maintain a custom kernel image long-term.

There's also the obvious point that a linux kernel module is useless on other platforms.