Bit banging a serial to parallel shift register to drive a 7 segment display is very slow.

[chrisidle]

I am trying to write a display multiplexer by bit banging a 16 bit register to an external serial to parallel shift register. The issue is that the code is running very slowly! I have tried to see how fast the device will run by writing a very simple while loop which sets and clears a pin (while(true){digitalWrite(D6,0);digitalWrite(D6,1):}) On the Espurino this code produces a square wave of about 4kHz. The same code running on a MicroBit using Make Code produces a square wave of about 300kHz. If i flash the Micro Bit with Espurino and run the code i get 4kHz. The issue must therefore be the Espurino code rather than the hardware. Does anyone have any thoughts or ideas as to how i can improve the performance. Thanks

[gfwilliams]

Hi,

As I understand it, Microsoft Make:code actually does some compilation on the code you write, so it's going to be a bit faster than running the JS which is interpreted from the text on the fly. Espruino has a bunch of options though...

• Use the E.shiftOut function which basically bit-bangs for you: https://www.espruino.com/Reference#l__global_shiftOut
• Just use SPI - hardware or even software SPI should be pretty quick and you can run it on whatever pins you want. You just convert the 16 bit number into 2 8 bit numbers which you can do with new Uint16Array([number]).buffer
• JIT-compile a JavaScript function - but that isn't in micro:bit builds, it's only official boards: https://www.espruino.com/JIT
• Use the compiler to compile C code: https://www.espruino.com/Compilation (again, only official boards)

There are other options too, but those are going to be the easiest/best.