Meadow - bit banging very slow

1

I’m driving a MAX7219 shift-register based display (8x 7-segment units) from a Meadow F7 using pins D00 - D02 (data, chip select and clock respectively).

My current implementation is bit-banging the digital I/O pins and is very slow - by my timings it takes ~15 - 16ms to toggle the state of a pin. This gives around 62 - 67 Hz update rate.

I’m aware that bit-banging is considered orders of magnitude slower than SPI etc, but this seems excessively slow and takes over 800ms to set a single digit on the MAX7219 (i.e. to bit-bang out 2 bytes).

I found an article where someone was able to drive the I/O pins of an STM32-series chip at over 1MHz without any great effort. I appreciate that bare-metal C doesn’t have the same overheads as a real-time OS running .NET, but this seems like an incredible difference.

Is this known / expected? Can we expect the I/O toggle speeds to improve as the firmware matures? Am I simply doing something very wrong?!

2

This is a known issue and someone is looking at performance.

Regards,
Mark

3

Thanks for the update Mark - are we likely to see this for Beta 4 or will it be further down the line?

4

We publish the Roadmap on the beta site.

I would expect it to be covered somewhere in Mono Linking and other optimisations

Out of curiosity, why not use SPI for the data transfer?

Regards,
Mark

5

Out of curiosity, why not use SPI for the data transfer?

Hadn’t realised that was an option - I’ll give it a go!