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ESP32-C3 has a nice feature called GPIO Matrix which allows to map most of it's peripherals to any GPIO pin. And it has feature called IO_MUX which allows direct & faster operations for some of the high speed peripherals, including SPI. The API from ESP-IDF (HAL SDK) provides some library documentation on SPI functions.

But Arduino-ESP32 core documentation seems to completely miss SPI library & it's functions. It refers to basic Arduino SPI class, but it lacks description of features ESP32 family has.

I've found this example for ESP32 (note that I'm looking for ESP32-C3 info) which sets SPI pins through SPI.begin method actually.

I've also found this source which seems to feature a lot of SPI internal HAL functions. And a C++ SPI class sources are here. But it's actually doesn't have any useful comments on how to use IO_MUX or allowed values for ::setFrequency() method.

So basically I'm asking for a documentation on ESP32-C3 Arduino specific SPI class features. But to narrow things down I'm actually looking now how to initialize SPI2 (which is the only generally available SPI master on C3) as IO_MUX at the fastest SPI clock speed possible from the Arduino core/SPI class. Any suggestions are also welcomed!

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    Hi NStorm, I know your post is from a while ago, but for everyone's and anyone's sake: I'm still figuring out how to use the GPIO Matrix with ESP32-C3 and Arduino, but if you are using Arduino with it, then the default pins for SPI2 are defined here. Depending on whether you're initializing the peripheral yourself or a device is doing it for you, there are ways to pass in a different SPI clock speed.
    – Nick S.
    Commented Jan 30, 2023 at 4:56

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