Expand description
Type-level enum representing the SPI operating mode
See the documentation on type-level enums for a discussion of the pattern.
The available operating modes are Master, MasterHWSS and Slave.
In Master mode, the SS signal must be handled by the user, so SS
must be NoneT. In MasterHWSS mode, the hardware drives the SS
line, so SomePad is required. In Slave mode, the SS pad is
required as well, to indicate when data is valid.