Support for Adafruit 16 channel pwm board

#1

I would like to use the Adafruit 16 channel pwm board on the Rock Pi 4, but the device tree overlay is not implemented in the kernel. I tried to compile the version from the Raspberry, but that didn’t work. Sadly I’m not familiar with the device tree compilation. Could someone help me to get this to work?

#2

Hi,

I think you can follow this one:

https://github.com/radxa/kernel/blob/release-4.4-rockpi4/arch/arm64/boot/dts/rockchip/overlays/at24c02-overlay.dts

It should be something like below:

/dts-v1/;
/plugin/;

/ {
	model = "ROCK PI 4B";
	compatible = "rockchip,rockpi","rockchip,rk3399";

	fragment@0 {
		target = <&i2c2>; /* Assume you connect the device to I2C2 */

		#address-cells = <1>;
			#size-cells = <0>;
			status = "okay";

			pca: pca@40 {
				compatible = "nxp,pca9685";
				#pwm-cells = <2>;
				reg = <0x40>;
				status = "okay";
			};
	};
};

You may also need to enable the pca9685 driver in kernel config.

#3

Thanks, I didn’t notice this dts file because of the different name. The file was already in my boot directory, so I simply uncommented the following line in hw_intfc.conf:

intfc:dtoverlay=at24c02

But after a reboot there is still no device on address 0x40. I’ve also compiled a new kernel with the PWM_PCA9685 config option, but also no device appears on address 0x40. But when I connect the board there appears a device on address 0x50 with i2cdetect -y 2:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

I’ve already tried to control the servos using the 0x50 address, but that didn’t work. Any ideas what could be the problem?

#4

The PCA9685 is very flexible with regard to its addresses and could well have the address 0x50, but the address must not change automatically. lol
As far as I know the addresses from 0x50 to 0x57 are used by all FRAM and EEPROM ICs.

#5

I’ve already tried the board on a Raspberry Pi 3 and there it appeared on address 0x40. So I think this is just an EEPROM from the board. Any ideas why the PCA9685 chip is not recognized?

#6

Excuse me, that was my fault! I read over what you did. You have unlocked exactly one I2C EEPROM available on the Rock Pi.

# Set "on" to enable the optional hardware interfaces while set "off" to disable.

intfc:pwm0=off
intfc:pwm1=off
intfc:uart2=off
intfc:uart4=off
intfc:spi1=off
intfc:spi2=off
intfc:i2c2=off
intfc:i2c6=off
intfc:i2c7=on

# Devicetree Overlay Enable, uncomment to enable .dtbo under /boot/overlays/.

# EEPROM on I2C2
#intfc:dtoverlay=at24c02

I did not touch the EEPROM for my test, but changed the off in the line with “intfc:i2c7=off” to an on.

#7

I’ve just tested that. I set intfc:i2c7 to on and commented out the line intfc:dtoverlay=at24c02 again and rebooted. But I can still only see the 0x50 address on i2c bus 2. Any other ideas?

Edit: Sorry, I didn’t realise that this simply activates i2c bus 7. I can see the address 0x40 on bus 7 now. I will now test if I can get some servos to run.

#8

@SunWukong Sadly the code I used on the Raspberry does not work on the Rock Pi 4 because it relies on the wiringpi library that is not compatible with this board. Are there any examples how to control pca9685 boards using the mraa library? I didn’t find anything so far.

#9

The UP board is definitely not a Raspberry Pi Clone and seems to work with the Adafruit HAT. And here they also work with the libmraa.

If you are using Ubuntu , you’ll need to install the MRAA library.

https://wiki.up-community.org/Adafruit#Using_Adafruit_16-Channel_PWM_.2F_Servo_HAT_on_UP

1 Like
#10

I’ve now installed libmraa as described here and it works with the Python test program. But I need to control the board from a Java application. There should be a package libmraa-java, but that package isn’t found in the Radxa repository. How can I install the java package?

1 Like
#11

The rockpi4-dtbo package should have jave support already. Just check the libmraa java examples.

https://github.com/intel-iot-devkit/mraa/tree/master/examples/java

#12

I’ve installed both rockpi4-dtbo and libmraa-rockpi4, but there is no libmraajava.so:

find /usr/ -name “mraa”
/usr/local/include/mraa.hpp
/usr/local/include/mraa
/usr/local/include/mraa.h
/usr/local/bin/mraa-gpio
/usr/local/bin/mraa-uart
/usr/local/bin/mraa-i2c
/usr/local/lib/libmraa.so
/usr/local/lib/python2.7/dist-packages/_mraa.so
/usr/local/lib/python2.7/dist-packages/mraa.py
/usr/local/lib/libmraa.so.2.0.0
/usr/local/lib/pkgconfig/mraa.pc
/usr/local/lib/libmraa.so.2
/usr/local/share/mraa
/usr/local/share/mraa/examples/c/hellomraa.c

For the moment I’ve compiled the library myself. But to write guides it would be much simpler if I could just provide an apt-get line to be executed. Do I miss a package? Or can I simply add the official mraa repository to install the java package?