Radxa Zero

The Radxa Zero is a single board SoC computer based on the Amlogic S905Y2 arm64 processor. It has built-in GPIO, I2C, PWM, SPI, 1-Wire and ADC interfaces.

For more info about the Radxa Zero, go to https://docs.radxa.com/en/zero/zero.

How to Install

Please refer to the main README.md

Tested OS:

dietPi a minimal image with Debian Bookworm

Configuration steps for the OS

WLAN access

There is no LAN network interface on the board, but WLAN is sufficient for our needs. After copy over the image to your SD card you can modify the file dietpi.txt before plug in the card to make it work on first boot.

txt

AUTO_SETUP_NET_WIFI_ENABLED=1
AUTO_SETUP_NET_WIFI_COUNTRY_CODE=DE

Afterwards the WiFi login data needs to be provided (unencrypted file, will be removed after first boot):

txt

aWIFI_SSID[0]="<name of your network>"
aWIFI_KEY[0]="<password>"

First login needs to be done with "root" or "dietpi", and you will start with a configuration procedure.

ssh root@DietPi

System access and configuration basics

Please follow the instructions of the OS provider. A ssh access for (WLAN with dietpi user) is used in this guide.

ssh dietpi@DietPi

Enabling hardware drivers in general

Not all drivers are enabled by default. You can have a look at the configuration file, to find out what is enabled at your system:

cat /boot/dietpiEnv.txt

Missing interfaces needs to be enabled by DT-overlays (drop "meson" prefix and file extension).

ls /boot/dtb/amlogic/overlay/

Please read this GPIO page for meaning of the different part of file name (e.g. "ao" vs. "ee"). The page about overlays will help you in addition to choose the right one.

enable I2C

device	SDA	SCL	DT overlay file name
/dev/i2c-1	16	13	meson-g12a-radxa-zero-i2c-ee-m1-gpiox-10-gpiox-11.dtbo
/dev/i2c-1	24	23	meson-g12a-radxa-zero-i2c-ee-m1-gpioh-6-gpioh-7.dtbo
/dev/i2c-3	3	5	meson-g12a-radxa-zero-i2c-ee-m3-gpioa-14-gpioa-15.dtbo
/dev/i2c-4	7	11	meson-g12a-radxa-zero-i2c-ao-m0-gpioao-2-gpioao-3.dtbo

...
overlays=g12a-radxa-zero-i2c-ee-m1-gpioh-6-gpioh-7
...

The I2C device "/dev/i2c-3" was already enabled on dietPi after setup.

enable SPI

...
overlays=g12a-radxa-zero-spi-spidev
...

Most likely the overlay is currently defective - it contains "armbian" and only "disabled" spi devices.

enable PWM

pin	symbol	DT path	driver	DT overlay file name
32, PWMAO_C	pwm_AO_cd	/soc/bus@ff800000/pwm@2000	meson-g12a-ao-pwm-cd	on by default
40, PWMAO_A	pwm_AO_ab	/soc/bus@ff800000/pwm@7000	meson-g12a-ao-pwm-ab	meson-g12a-radxa-zero-pwmao-a-on-gpioao-11.dtbo
18, PWM_C	pwm_cd	/soc/bus@ffd00000/pwm@1a000	meson-g12a-ee-pwm	meson-g12a-radxa-zero-pwm-c-on-gpiox-8.dtbo
21, PWM_F	pwm_ef	/soc/bus@ffd00000/pwm@19000	meson-g12a-ee-pwm	on by default

PWMAO_B (channel 1 of pwm_AO_ab) and PWM_D (channel 1 of pwm_cd) not wired. PWMAO_D (channel 1 of pwm_AO_cd) in use by "regulator-vddcpu". PWM_E (channel 0 of pwm_ef) in use by wifi32k. PWMAO_C and PWM_F not really working, see troubleshooting section.

enable 1-wire

The contained overlays maybe not working, because compatible with gxbb (Amlogic Meson S905). At least for my Zero V1.51 g12a (Amlogic Meson S905X2 and above) it does not work.

dtc -I dtb -O dts /boot/dtb/amlogic/overlay/meson-w1AB-gpio.dtbo | grep amlogic
...
compatible = "amlogic,meson-gxbb";

So create your own overlay as /boot/overlay_user/meson-g12a-w1-gpioao-3.dts...

/dts-v1/;
/plugin/;

/ {
	compatible = "radxa,zero", "amlogic,g12a";

	fragment@0 {
		target-path = "/";

		__overlay__ {
			w1: onewire {
				compatible = "w1-gpio";
				pinctrl-names = "default";
				/* GPIOAO_3=0x03, GPIOC_7=0x30 */
				/* GPIO_ACTIVE_HIGH=0, GPIO_ACTIVE_LOW=1 */
				/* GPIO_SINGLE_ENDED=2, GPIO_LINE_OPEN_DRAIN=4 */
				gpios = <0xffffffff 0x03 0x06>;
				status = "okay";
				phandle = <0x01>;
			};
		};
	};

	__fixups__ {
		/* gpio_ao or gpio for GPIOC_7 */
		gpio_ao = "/fragment@0/__overlay__/onewire:gpios:0";
	};
};

...compile it

dtc -@ -O dtb -b 0 -o meson-g12a-w1-gpioao-3.dtbo meson-g12a-w1-gpioao-3.dts

... and add it as follows:

...
user_overlays=<existing names> meson-g12a-w1-gpioao-3
...

enable SAR ADC

The 12-bit ADC is enabled by default. The voltage range is 0..1.8V. Raw values can be read with pin 15 (channel 1) or pin 26 (channel 2). Additionally some internal values can be accessed, e.g. gnd and 1/4 vdd. For debugging purposes more information is provided, e.g. each item provides a label:

cat /sys/bus/platform/drivers/meson-saradc/ff809000.adc/iio:device0/in_voltage9_label
gnd
cat /sys/bus/platform/drivers/meson-saradc/ff809000.adc/iio:device0/in_voltage10_label
0.25vdd

cat /sys/bus/platform/drivers/meson-saradc/ff809000.adc/iio:device0/calibbias
-4
cat /sys/bus/platform/drivers/meson-saradc/ff809000.adc/iio:device0/calibscale
1.002447
cat /sys/bus/platform/drivers/meson-saradc/ff809000.adc/iio:device0/in_voltage_scale
0.439453125
cat /sys/bus/platform/drivers/meson-saradc/ff809000.adc/iio:device0/in_voltage9_raw
0
cat /sys/bus/platform/drivers/meson-saradc/ff809000.adc/iio:device0/in_voltage10_raw
1023

The in_voltage_scale (e.g. 0.439453125) is for calculation of "value = (raw + offset) * scale", value in millivolts. The calibbias is the offset and calibscale the scale which is used for internal calibration, so we get an output of 0..4095 for 0..1.8V input.

The channel 10 is a 1/4 of full range, but if the channel 2 is in saturation state (above 1.8V = 4095), it becomes more and more wrong.

How to Use

The pin numbering used by your Gobot program should match the way your board is labeled right on the board itself.

r := zero.NewAdaptor()
led := gpio.NewLedDriver(r, "7")

How to Connect

Compiling

Compile your Gobot program on your workstation like this:

GOARCH=arm64 GOOS=linux go build -o output/ examples/zero_blink.go

Once you have compiled your code, you can upload your program and execute it on the board from your workstation using the scp and ssh commands like this:

scp zero_blink dietpi@DietPi:~
ssh -t dietpi@DietPi "./zero_blink"

Troubleshooting

scp fails

"bash: line 1: /usr/lib/sftp-server: No such file or directory"

The dietPi has only a limited package set, so sftp-server is missing.

sudo apt install openssh-sftp-server

GPIO pin3, pin5 and pin7 not working like expected

e.g. for pin3: cdev.Export(): cdev.reconfigure(gpiochip0-63)-c.RequestLine(63, [0 2000000000 2]): invalid argument

The pin does not support adaptors.WithGpioDebounce(inPinNum, debounceTime).

cdev.Export(): cdev.reconfigure(gpiochip1-0)-c.RequestLine(0, [0 2]): invalid argument

The pin 8 is configured for UART.

Some pins have low power or have a strong pullup resistor, so the expected voltage drop is maybe not possible. Pins 7-27 and 11-28 are bridged.

PWMAO_C and PWM_F not really working

If you run cat /sys/kernel/debug/pwm when those PWMs are used you can see, that it is working "internally". Most likely the pin itself is not enabled by DT on PWM usage. Currently there is no fix provided for that.