Example Device: DEBIX Model A + I/O Board
Overview
lThe model of Ultrasonic Distance Measuring Module is HC-SR04.
lApply a 10us high level signal to the Trig end, and the Echo end will receive a response level that is proportional to the measurement distance.
lThe distance calculation formula is: distance (m) = high level time * speed of sound (340m/s)/2.
Hardware installation
lUltrasonic module's VCC terminal is connected to J2 Pin2 of DEBIX I/O board
lUltrasonic module's Trig terminal is connected to J2 Pin33 of DEBIX I/O board
lUltrasonic module's Echo terminal is connected to J2 Pin31 of DEBIX I/O board
lUltrasonic module's GND terminal is connected to J2 Pin39 of DEBIX I/O board
Modify the device tree imx8mp-evk.dts
1. Add the GPIO to be used under iomuxc node:
pinctrl_HC_SR04: SR04group{
fsl,pins = <
MX8MP_IOMUXC_SPDIF_RX__GPIO5_IO04 0x40000
MX8MP_IOMUXC_SPDIF_TX__GPIO5_IO03 0x40000
>;
};
2. Add the ultrasonic module node under the root node:
hc_sr04: hc_sr04 {
compatible = "HC_SR04";
pinctrl-0 = <&pinctrl_HC_SR04>;
trig-gpios = <&gpio5 03 GPIO_ACTIVE_LOW>;
echo-gpios = <&gpio5 04 GPIO_ACTIVE_LOW>;
};
3. Add outside the root node:
&hc_sr04 {
status = "okay";
};
4. Compile and replace the device tree file
lCompile the device tree in the source directory: make ARCH=arm64 CROSS_COMPILE=aarch64-none-linux-gnu- dtbs
lCopy the compiled new device tree file arch/arm64/boot/dts/freescale/imx8mp-evk.dtb to the /boot directory of DEBIX and restart DEBIX.
5. Check whether dts contains the modified device tree node.
lRun the command ls /sys/firmware/devicetree/base/hc_sr04/
l Run the command cat /sys/firmware/devicetree/base/hc_sr04/compatible
