128x128 SPI display artifacts

skeller · January 12, 2022, 7:18am

Does anyone have any idea why I am getting gibberish on the far right and bottom edges of the screen?
Using this display: 128x128 1.45" Full Color TFT LCD Display from Crystalfontz

Here is how I am initializing the display:

private static ST7735Controller st7735;
private const int SCREEN_WIDTH = 128;
private const int SCREEN_HEIGHT = 128;

    public  void Init()
    {
        var spi = SpiController.FromName(SC20100.SpiBus.Spi3);
        var gpio = GpioController.GetDefault();
        


        st7735 = new ST7735Controller(
            spi.GetDevice(ST7735Controller.GetConnectionSettings(SpiChipSelectType.Gpio, gpio.OpenPin(SC20260.GpioPin.PA14))), //CS pin.
            gpio.OpenPin(SC20260.GpioPin.PB0), //RS pin.
            gpio.OpenPin(SC20260.GpioPin.PA15), //RESET pin.
            ScreenSize._128x128
        );

        var backlight = gpio.OpenPin(SC20260.GpioPin.PE11);
        backlight.SetDriveMode(GpioPinDriveMode.Output);
        backlight.Write(GpioPinValue.High);
        st7735.SetDataFormat(DataFormat.Rgb565);
        st7735.SetDataAccessControl(false, true, true, true); //Rotate the screen.
        st7735.SetDrawWindow(0, 0, SCREEN_WIDTH - 1, SCREEN_HEIGHT - 1);
        st7735.Enable();
	
    // Create flush event
        Graphics.OnFlushEvent += Graphics_OnFlushEvent;

        // Create bitmap buffer
        screen = Graphics.FromImage(new Bitmap(SCREEN_WIDTH, SCREEN_HEIGHT));

}

Brett · January 12, 2022, 9:44am

no real idea but i suspect that you might find those cells are outside your draw window area. I’d try playing with graphics items like boxes and putting them on sides and top and bottom, to make sure the screen and driver haven’t “wrapped” each other and you lose one pixel on top and it pushed a random bit of memory to the bottom from the display buffer… I remember something similar that needed tweaking when i worked on the ili9341 netmf drivers ( [poundy/Vecc.Netmf.Drivers.Ili9341: Display driver for the .NET Micro Framework to drive the ILI9341 LCD screens (here) but don’t recall exactly what I found they were doing wrong.

Dat_Tran · January 12, 2022, 2:02pm

Looks to me that it is 130x132 :)). Draw Pixel 0 is blue, 1 to 126 is White, 127 is Red to see actual size of the screen.

skeller · January 12, 2022, 11:51pm

This fixed the issue:
st7735.SetDrawWindow(2, 3, SCREEN_WIDTH - 1, SCREEN_HEIGHT - 1);

Brett · January 13, 2022, 4:20am

but clearly lost you a few pixels - and they’re scarce resources to start ! Anyway, if that’s an OK solution, go for it. I’d want to play more before giving in (because to me it looks “code” not hardware)

skeller · January 13, 2022, 5:32am

It doesn’t loose any pixels. I found the solution when comparing the TinyCLR driver with the demo code from the display provider. (Code is available if you follow the link in the original post.)

This is their version of SetDrawWindow():

void Set_LCD_for_write_at_X_Y(uint8_t x, uint8_t y)
  {
  //CASET (2Ah): Column Address Set
  // * The value of XS [15:0] and XE [15:0] are referred when RAMWR
  //   command comes.
  // * Each value represents one column line in the Frame Memory.
  // * XS [15:0] always must be equal to or less than XE [15:0]
  SPI_sendCommand(ST7735_CASET); //Column address set
  //Write the parameters for the "column address set" command
  SPI_sendData(0x00);     //Start MSB = XS[15:8]
  SPI_sendData(0x02 + x); //Start LSB = XS[ 7:0]
  SPI_sendData(0x00);     //End MSB   = XE[15:8]
  SPI_sendData(0x81);     //End LSB   = XE[ 7:0]
  //Write the "row address set" command to the LCD
  //RASET (2Bh): Row Address Set
  // * The value of YS [15:0] and YE [15:0] are referred when RAMWR
  //   command comes.
  // * Each value represents one row line in the Frame Memory.
  // * YS [15:0] always must be equal to or less than YE [15:0]
  SPI_sendCommand(ST7735_RASET); //Row address set
  //Write the parameters for the "row address set" command
  SPI_sendData(0x00);     //Start MSB = YS[15:8]
  SPI_sendData(0x01 + y); //Start LSB = YS[ 7:0]
  SPI_sendData(0x00);     //End MSB   = YE[15:8]
  SPI_sendData(0x80);     //End LSB   = YE[ 7:0]
  //Write the "write data" command to the LCD
  //RAMWR (2Ch): Memory Write
  SPI_sendCommand(ST7735_RAMWR); //write data
  }

This is TinyCLR’s version:

public void SetDrawWindow(int x, int y, int width, int height) {
    this.Width = width;
    this.Height = height;

    this.buffer4[1] = (byte)x;
    this.buffer4[3] = (byte)(x + width);
    
    this.SendCommand(ST7735CommandId.CASET);
    this.SendData(this.buffer4);

    this.buffer4[1] = (byte)y;
    this.buffer4[3] = (byte)(y + height);
    
    this.SendCommand(ST7735CommandId.RASET);
    this.SendData(this.buffer4);
}

You can see that they add some padding to the X and Y bytes that the TinyCLR driver does not:
SPI_sendData(0x02 + x);
SPI_sendData(0x01 + y);

Why the ‘3’ works for the ‘y’ option when they have a ‘1’, I don’t have a good answer. But in the end it works.

Dat_Tran · January 13, 2022, 2:00pm

There is 132x130 support by driver as well. You can try that to see what actual screen size is.

 public ST7735Controller(SpiDevice spi, GpioPin control, GpioPin reset, ScreenSize screenSize)

If actual size is 132x130 and set draw window is 128x128 then won’t lost any pixel of course, just because draw window is smaller, doesn’t mean actual is 128x128.

Gus_Issa · January 13, 2022, 2:23pm

I think it is impossible to know what configuration reach display has. It is normal that the physical display may not start at address 0, meaning draw window will need to be adjusted accordingly.

skeller · January 13, 2022, 6:23pm

With the current settings, I have no loss of pixels. I did draw pixel 0 blue, and 127 red and they are where they are supposed to be. It appears with this particular display the physical rows and columns are mapped slightly offset from the RAM addresses.

Dat_Tran · February 8, 2022, 8:09pm

Can you please provide detail what you changed, so we can apply your code exactly without testing because we don’t have that screen for quick test?

skeller · February 8, 2022, 8:39pm

This is what worked for me.

private const int SCREEN_WIDTH = 128;
private const int SCREEN_HEIGHT = 128;

st7735.SetDataFormat(DataFormat.Rgb565);
st7735.SetDataAccessControl(false, true, true, true); //Rotate the screen.
st7735.SetDrawWindow(2, 3, SCREEN_WIDTH - 1, SCREEN_HEIGHT - 1);
st7735.Enable();

I don’t seem to lose any pixels, I have the full 128 both x and y.

I didn’t make any changes to the driver software. Setting the draw window with x = 2, y = 3 seemed to solve the issue and still use the default 7735 driver software.

Dat_Tran · February 8, 2022, 8:48pm

I think we don’t need to change driver, because your workaround looks good to us.

skeller · February 9, 2022, 4:35am

Sounds good. Thanks for looking into it.