ST7735 at high rate?

[espruino-discuss]

Posted at 2024-05-09 by Mrbbp

Hello, i'm back from a long circuitpython session...

I'm playing with a small 128x128 SPI TFT display with a short generative prog

const s = require("Storage");
const largeur = 32;
function ecrit() {
  console.log("écrit");
  g.clear();
  var start = getTime();
  for (let y = 0; y<128; y+=largeur) {
    for (let x = 0; x<128; x+=largeur) {
      if (Math.random()>0.5) {
        g.setColor(1);
        g.fillRect(x,y,x+largeur,y+largeur);
      } 
    }
  }
  print("dessine:",getTime()-start);
  g.flip(); //<--- Send to the display
  print("affiche:",getTime()-start);
}

var g;
function onInit() {
  var colorPalette = new Uint16Array([0xFFF, 0]);
  // init spi
  var spi = new SPI();
  spi.setup({mosi:B15 /* sda */, sck:B13 /* scl */});
  g =require("ST7735").connect({
    palette:colorPalette,
    spi:spi,
    dc:A7,
    cs:B10,
    rst:B1,
    padx:2,
    pady:3
    // height : 160 // optional, default=128
    }, setInterval(ecrit, 500)
  );
  console.log("## mém. used: " + Math.round(process.memory().usage / process.memory().total * 100) + "% ##");
  s.getFree();
}

But the display take 0.65sec to screen the picture drawn in .02s
Is there a way to send faster to the display?
and avoid image scanning?

regards

[espruino-discuss]

Posted at 2024-05-09 by Mrbbp

i tried with an hardware spi, but I don't save much time. 1 tenth of a second

SPI2.setup({mosi:B15 /* sda */, sck:B13 /* scl */, baud:integer=1000000,});
  g =require("ST7735").connect({
    palette:colorPalette,
    spi:SPI2,
    dc:A7,
    cs:B10,
    rst:B1,
    padx:2,
    pady:3
    // height : 160 // optional, default=128
    }, ecrit
  );

---

Posted at 2024-05-09 by @fanoush

  var spi = new SPI();
  spi.setup({mosi:B15 /* sda */, sck:B13 /* scl */});

You could use hardware SPI and set higher speed?

Also you could try to enable JIT compiler in the flip() method
https://www.espruino.com/modules/ST7735.js
but that may not help that much.

Also there is the relatively generic lcd_spi driver
https://github.com/espruino/Espruino/blob/master/libs/graphics/lcd_spilcd.c
that could maybe work with ST7735

---

Posted at 2024-05-09 by @fanoush

baud:integer=1000000

why so low (1Mbit)? these displays can do much more, 16 or even 32Mbit could work (not sure what is the limit of your board)

---

Posted at 2024-05-09 by Mrbbp

thank you.
i do not investigate which baud i could use.
I've tried with 32Mbits and a delay of 50ms between each frame. It works but i take 0.4s (30 percent better) but 2.5 frame/sec.
and with an ugly scanning refresh.

---

Posted at 2024-05-10 by @gfwilliams

The ST7735 module does use an offscreen buffer. Some modules for driving screens (like https://www.espruino.com/ST7789) offer a mode where they render direct to the screen, so you could try copy/pasting the code to do that instead.

Sending direct causes more flicker but if you're not overwriting much of the screen it could be faster.