SPI communication

1. SPI functional features

SPI (serial peripheral interface). The following are some features supported by the Linux 4.4 SPI driver:

  • The Motorola SPI protocol is adopted by default.
  • Supports 8-bit and 16-bit.
  • The software-programmable clock frequency and transmission rate can reach up to 50MHz.
  • Supports the configuration of 4 SPI transmission modes.
  • Each SPI controller supports one to two chip selects.
  • The framework supports both slave and master modes.

2. SPI pins

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SPIPINFunctions
MOSI19Master Output/Slave Input (MOSI)
MISO21Master Input/Slave Output (MISO)
CLOCK23Clock Signal Line
CS024Chip Select Signal Line 0

Warning

spidev3.0 controls CS0

3. Device Tree Source (DTS) configuration

Enable SPI in arch/arm64/boot/dts/rockchip/rk3568-toybrick-x0-linux.dts.

    &spi3 {
        status = "okay";
        pinctrl-0 = <&spi3m1_cs0  &spi3m1_pins>;
        pinctrl-1 = <&spi3m1_cs0  &spi3m1_pins_hs>;
        spidev:spidev@0 {
                compatible = "rockchip,spidev";
                reg = <0>;
                spi-max-frequency = <10000000>;
                status = "okay";
        };
    };

4. Check the SPI device

Enter the following commands in the board's terminal to check whether the SPI device is created

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5. SPI loopback test

Short-circuit the MOSI and MISO (it is recommended to use a jumper cap for short-circuiting to ensure data stability).

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Use the loopback test program available online to test whether the SPI is working properly.

When short-circuiting, the data is correct.

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When there is no short-circuiting, the data appears as garbled characters.

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