Port an MBED design to non-MBED - Phase 2a: DigitalOut Class Constructor

RE: Port an MBED design to non-MBED - Phase 2a: DigitalOut Class Constructor

Jan Cumps — Tue, 12 Nov 2019 16:37:51 GMT

The port of this class is now complete. See here for the full code an some explanation.

I have made some changes to the constructor. The one described here needs board knowledge (the pin and port data members). In the final version that is abstracted out to the board dependent definitions.

RE: Port an MBED design to non-MBED - Phase 2a: DigitalOut Class Constructor

fmilburn — Mon, 11 Nov 2019 22:24:08 GMT

Hi Jan,

I believe there is a typo

What I did id somewhat sneakier, and controversial on a 32-bit microcontroller.
I defined the PinName type as a 32 bit unsigned integer.

PinName is uint64_ so 64 bit.

Is this approach controversial because not all microcontrollers implement 64 bit integers? I am learning a lot from reading this series btw.

RE: Port an MBED design to non-MBED - Phase 2a: DigitalOut Class Constructor

Jan Cumps — Mon, 11 Nov 2019 22:09:24 GMT

STM did it simpler, but not unlike me.

// High nibble = port number (FirstPort <= PortName <= LastPort)

// Low nibble = pin number

#define STM_PORT(X) (((uint32_t)(X) >> 4) & 0xF)

#define STM_PIN(X) ((uint32_t)(X) & 0xF)

They can do that because in their API, the ports aren't 32 bit addresses but a low number like 1, 2, 3.

I could have kept it to a single 32 bit variable too with a little redirection, by putting all the available I/O ports in lookup table (there are a decent lot, because you can use almost all peripherals as I/O).

Then my high nibble would be the index into that table.