Espruino on the Cardputer

[joakim]

Thanks to recent improvements to the ESP32 build by @SimonGAndrews, Espruino now runs on my Cardputer!

To me, the Cardputer is the ideal Espruino device. It has Wifi, BLE, 1.14" display, keyboard, speaker, mic, microSD slot, battery and a Grove port for peripherals. Mine is the older version. The improved Cardputer ADV has a more responsive I2C keyboard, 14 GPIO pins on the back and a better antenna.

My goal is to make the Cardputer into a portable Espruino microcomputer. With the microSD card slot, it can carry all the modules and "apps" I need. The dream would be to have a command-line OS with the ability to edit files and launch apps, making it a full-fledged personal computer.

To keep myself on the ground, however, I think a simple Espruino console will have to do for now.

So far, I've gotten it to work as a VT100 terminal. The display was easy, as it was already supported by the ST7789 module. I then added rudimentary support for the 4x14 keyboard matrix and used the VT100 module to get a terminal on the display.

Code

let LOWER = "\u001ezcbm. \u000fsfhk:\nqetuo[\\13579-\b\u001d\u001fxvn,/\u001cadgjl'\twryip]`24680+";
let UPPER = "\u001eZCBM> \u000fSFHK;\nQETUO{|!#%&(_\b\u001d\u001fXVN<?\u001cADGJL\"\tWRYIP}~@$^*)=";
let SHIFT = 7;

let A = [D8, D9, D11];
let Y = [D13, D15, D3, D4, D5, D6, D7];
Y.forEach(pin => pin.mode('input_pullup'));

let term;
let shift = false;

function scanKeyboard() {
  // Scan all possible address selectors
  for (let i = 0; i < 8; i++) {
    A[0].write(i & 0b1);
    A[1].write(i & 0b10);
    A[2].write(i & 0b100);

    // Scan all columns for this address selector
    for (let j = 0; j < 7; j++) {
      let state = digitalRead(Y[j]);
      let key = (i * 7) + j;
      if (state === 0) {
        if (key === SHIFT) {
          shift = true;
        }
        else {
          LoopbackB.write((shift ? UPPER : LOWER)[key]);
        }
      }
      else {
        if (key === SHIFT) shift = false;
      }
    }
  }
}

function onInit() {
  let spi = new SPI();
  spi.setup({ mosi: D35, sck: D36 });

  let g = require('ST7789').connect(spi, D34, D37, D33, () => {
    g.clear();
    g.setRotation(1);
    g.setFont('6x8');
  });

  term = require('VT100').connect(g, {
    charWidth : 8,
    charHeight : 12,
    marginTop : 4,
    marginLeft : 4,
    marginBottom : 4,
  });

  LoopbackB.on('data', function (e) {
    for (let i in e) term.char(e[i]);
  });

  Serial1.on('data', function (e) { LoopbackB.write(e); });

  LoopbackA.setConsole();

  setInterval(scanKeyboard, 10);
}

Video

Sorry for the unsteady camera…

It works, which is really cool! But it is also very slow and a bit buggy. First, the ST7789 module is not native but runs in the JavaScript interpreter. Second, my older Cardputer uses a demultiplexer for the keyboard matrix which requires checking which keys are pressed every few ms, no interrupts. So the keys require long/hard presses to register, after which the display takes a moment to update, making it all feel very sluggish. And for some reason, it doesn't scroll.

I'm now thinking a better approach would be a custom Espruino build. Use M5Stack's M5Cardputer library, with M5GFX (based on LovyanGFX) instead of the ST7789 module for the display, and provide a JS API for the keyboard and other peripherals. And like the Pixl, provide a built-in Terminal. That is a much larger undertaking.

I've not done a ton of C and have only just looked around in the Espruino code base, so I'm not sure if I can pull it off on my own. But there's only one way to find out, so I think I will give it a try. If anybody is interested in helping out, you'll be more than welcome!

https://github.com/joakim/Espruino-Cardputer

[gfwilliams]

That's great! Glad you got it going!

You may well be able to build your own firmware using SPILCD that's inside Espruino: https://github.com/espruino/Espruino/blob/master/libs/graphics/lcd_spilcd.c (or lcd_spi_unbuf) - that should be a lot faster.

For the keyboard, I'm not sure if https://www.espruino.com/KeyPad will work? It uses watches on the matrix lines which means it doesn't have to keep polling - it knows when a key is pressed. But I don't know if ESP32 can do enough watches

[joakim]

You may well be able to build your own firmware using SPILCD that's inside Espruino

Thanks for the tip! I'll try that then. Should make the build smaller as well.

For the keyboard, I'm not sure if https://www.espruino.com/KeyPad will work?

I don't think so. My older Cardputer uses a 74HC138 3-to-8-line decoder/demultiplexer. If I understand correctly, it doesn't support interrupts. The original C++ code iterates over all columns for each combination of the 3 address select pins.

I am tempted to just buy the ADV version with an I2C keyboard, but it would be nice to support the older Cardputers as well. So I think I'll want to use the M5Cardputer library for the keyboard. Does that seem doable?

[joakim]

I noticed there's an LCD_ST7789_8BIT library that's used by Bangle and Emscripten. Could I use that? The display is ST7789V2 (240 x 135).

Edit: Having had a closer look, lcd_spi_unbuf seems easier anyway, so I'll try that first.

[gfwilliams]

Is the display connected in parallel or SPI? My guess was SPI which is why I suggested the earlier one. There's also LCD_FSMC for completey parallel displays.

Shame about having to use the demultiplexer. It might be possible to use their library, but if you're building stuff in I'd be tempted to do it yourself. microbit for instance has to scan out the display in an interrupt (https://github.com/espruino/Espruino/blob/master/libs/microbit/jswrap_microbit.c#L59) so you could use that same code to scan out the multiplexer in an interrupt

[joakim]

It is SPI. I found the LCD_SPI_UNBUF library and have successfully built my custom board, but haven't gotten the display to work yet. Will keep at it :)

Shame about having to use the demultiplexer. It might be possible to use their library, but if you're building stuff in I'd be tempted to do it yourself.

I'm also tempted to try to do it myself, both to save space and to learn. I'll have a go at the jstExecuteFn approach.

Thank you so much for your helpful tips and pointers! I know I can't expect any support for this board, as it's not an official one. At least I'm learning the innards of Espruino along the way, and I hope to be able to contribute some code back as well.