Roadrunner technical documentation

Use 2.8 inch TFT displays on SPI ports

This article explains how to wire and manage up two 2.8" inch graphic display 240x320 wired on the SPI ports of a RoadRunner SOM.

Unfortunately on SAMD2 architecture is not available the driver to manage the resistive touch available on XTERM-01

Kernel menuconfig

Enable the kernel SPI drivers as explained here:

Enable the Kernel support for small TFT LCD with ILI9341 LCD Controller

Device Drivers  --->
  [*] Staging drivers  --->
    <*>   Support for small TFT LCD display modules  --->
            <*>   FB driver for the ILI9341 LCD Controller

Example 1: One display on each SPI

In this example we will use our XTERM-01 wired to Berta Board D2 evaluation kit using the port SPI0 and SPI1 lines (MOSI, MISO, CLK and CS) plus some extra signals required by the display (reset and data/command).


FIRST DISPLAY ON SPI0                   SECOND DISPLAY

| Signal     | Berta D2 | XTerm 0 |   | Signal     | Berta D2 | XTerm 1 |
|------------|----------|---------|   |------------|----------|---------|
| SPI0 MOSI  | PA15     | J4.8    |   | SPI1 MOSI  | PC2      | J4.8    |
| SPI0 MISO  | PA16     | J4.10   |   | SPI1 MISO  | PC3      | J4.10   |
| SPI0 SCLK  | PA14     |  J4.7   |   | SPI1 SCLK  | PC1      | J4.7    |
| SPI0 CS0   | PA17     | J4.25   |   | SPI1 CS0   | PC4      | J4.25   |
|            |          |         |   |            |          |         |
| Reset      | PA13     | J4.33   |   | Reset      | PC5      | J4.33   |
| D/C        | PA12     | J4.31   |   | D/C        | PC6      | J4.31   |
|            |          |         |   |            |          |         |
| 3V3        | 3V3      |  J4.5   |   | 3V3        | 3V3      | J4.5    |
| GND        | GND      |  J4.9   |   | GND        | GND      | J4.9    |
!------------|----------|---------|   |------------|----------|---------|

Device tree definition

/* Enable the SPI port 0 for a display selected by CS0 signal */

spi0: spi@f8000000 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_spi0_default>;
    status = "okay";

    device@0 {
        rotate = <90>;
        bgr;
        fps = <30>;
        compatible = "ilitek,ili9341";
        spi-max-frequency = <50000000>;   
        reg = <0>;
        regwidth = <8>;
        buswidth = <8>;
        verbose = <3>;
        reset-gpios = <&pioA PIN_PA13 0>;
        dc-gpios = <&pioA PIN_PA12 0>;
    };
};


/* Enable the SPI port 1 for a display selected by CS0 signal */

spi1: spi@fc000000 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_spi1_default>;
    status = "okay";

    device@0 {
        rotate = <90>;
        bgr;
        fps = <30>;
        compatible = "ilitek,ili9341";
        spi-max-frequency = <50000000>;   
        reg = <0>;
        regwidth = <8>;
        buswidth = <8>;
        verbose = <3>;
        reset-gpios = <&pioA PIN_PC5 0>;
        dc-gpios = <&pioA PIN_PC6 0>;
    };
};

Example 2: Two displays on the same each SPI

In this example we will use our XTERM-01 wired to Berta Board D2 evaluation kit using the port SPI1 lines (MOSI, MISO, CLK, CS0 and CS1) plus some extra signals required by the display (reset and data/command).


The CS0 and CS1 signals will be used to select the display

| Signal     | Berta D2 | XTerm 0 | XTerm 1 |
|------------|----------|---------|---------|
| SPI1 MOSI  | PC2      | J4.8    | J4.8    |
| SPI1 MISO  | PC3      | J4.10   | J4.10   |
| SPI1 SCLK  | PC1      | J4.7    | J4.7    |
|            |          |         |         |
| SPI1 CS0   | PC4      | J4.25   |         |
| Reset  0   | PA13     | J4.33   |         |
| D/C    0   | PA12     | J4.31   |         |
|            |          |         |         |
| SPI1 CS1   | PC5      |         | J4.25   |
| Reset  1   | PA11     |         | J4.33   |
| D/C    1   | PA8      |         | J4.31   |
|            |          |         |         |
| 3V3        | 3V3      | J4.5    | J4.5    |
| GND        | GND      | J4.9    | J4.9    |
!------------|----------|---------|---------|

Device tree definition

/* Enable the SPI port 1 */

spi1: spi@fc000000 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_spi1_default>;
    status = "okay";

    /* Display 0 selected by CS0 */

    device@0 {
        rotate = <90>;
        bgr;
        fps = <30>;
        compatible = "ilitek,ili9341";
        spi-max-frequency = <50000000>;   
        reg = <0>;
        regwidth = <8>;
        buswidth = <8>;
        verbose = <3>;
        reset-gpios = <&pioA PIN_PA13 0>;
        dc-gpios = <&pioA PIN_PA12 0>;
    };

    /* Display 0 selected by CS1 */

    device@1 {
        rotate = <90>;
        bgr;
        fps = <30>;
        compatible = "ilitek,ili9341";
        spi-max-frequency = <50000000>;   
        reg = <1>;
        regwidth = <8>;
        buswidth = <8>;
        verbose = <3>;
        reset-gpios = <&pioA PIN_PA11 0>;
        dc-gpios = <&pioA PIN_PA8 0>;
    };
};

Frame buffer

The display will be managed by Linux using these two devices:

/dev/fb0
/dev/fb1

It will be initializated at startup.

Using QT5

The QT5 applications can select on which display send the output in this form:

/usr/lib/qt/examples/widgets/widgets/calculator/calculator -platform linuxfb:fb=/dev/fb0 
/usr/lib/qt/examples/widgets/widgets/calculator/calculator -platform linuxfb:fb=/dev/fb1

Links

Sergio Tanzilli
Systems designer, webmaster of www.acmesystems.it and founder of Acme Systems srl

Personal email: tanzilli@acmesystems.it
Web pages: https://www.acmesystems.it --- https://www.acmestudio.it
Github repositories: https://github.com/tanzilli --- https://github.com/acmesystems
Telegram group dedicated to the Acme Systems boards: https://t.me/acmesystemssrl

Roadrunner technical documentation