1-wire Bus

To provide 1-Wire Bus Connections between various 1-Wire- and Hostdevices different connection methods can be used. They can be connected to a Host using a bus converter. USB, RS-232 serial port interfaces are popular solutions for connecting 1-Wire Devices to the Hostdevice. But 1-Wire devices can also be interfaced directly to Controllers from various vendors using a GPIO Pin.

This guide will only cover 1-Wire Bus Connections (as of Sep 13, 2019) up to the stable release v19.07.8. For newer Kernels (since v21.02.0) the Package “kmod-w1-gpio-custom” is no longer available. Therefore the Installation is a bit more extensive. The Device which got tested was a OrangePI PC+.

In order to use a GPIO for the 1-Wire bus, i.e. for using DS18B20 Sensors it is necessary to install several additional packages:

opkg update
opkg install kmod-w1 kmod-w1-master-gpio kmod-w1-gpio-custom kmod-w1-slave-therm

Configure the GPIO pin connected to the data line of the sensor. The Section “Software” in this howto describes how to determine the GPIO.

Create/Edit /etc/modules.d/55-w1-gpio-custom, replace 19 with the GPIO which you determined in the last step. You can include several bus definitions up to a maximum of four, i.e.:

echo "w1-gpio-custom bus0=0,19,0 bus1=1,20,0" > /etc/modules.d/55-w1-gpio-custom

The last Zero of the sequence means “not open-drain” and should be set to “0”.

After modifying the file /etc/modules.d restart, so that the kernel can load the modules.

When the 1-Wire bus is successfully set up, you should see in /sys/devices a directory called “w1_bus_master1”. A second bus will appear as “w1_bus_master2” and so on. Within this directory you will find a number of files including “w1_master_slaves_count” which shows the number of detected devices connected to the 1-Wire bus, and “w1_master_slaves” which contains a list of the device identifiers.

In case, it is a Sunxi Device and you like to connect e.g. Pin 29 (=PA7) Sunxi says:

(position of letter in alphabet - 1) * 32 + pin number

so the GPIO for PA7 would be ( 1 - 1) * 32 + 7 = 0 + 7 = 7 (since 'a' is the first letter).

(Or you take a look with

cat /sys/kernel/debug/pinctrl/1c20800.pinctrl/pins

for the mappings…)

This results in the following configuration

echo "w1-gpio-custom bus0=0,7,0" > /etc/modules.d/55-w1-gpio-custom

There are several possible Ways to install. The Way described here assumes, that an Image has been installed on a SD card.

This Description again refers to an Orange Pi PC+, Pin “PA3” is to be used as W1 port conected with DS18B20 Sensors.

First install the necessary several additional packages:

opkg update
opkg install kmod-w1 kmod-w1-master-gpio kmod-w1-slave-therm

As of v21.02.0 the Configuration of the Driver is done via the Device Tree. On your Computer you need a Device-Tree-Compiler installed. Several Linux Distributions have it available in the Repositys.

The Device Tree can be changed as follows:

  • Connect the SD Card to your Computer and look at lsblk or dmesg to identify it. In most Cases, it would be something like /dev/sdX.
  • Mount and open the “20M” Boot Partition.
  • there are 3 Files in the Partition: boot.scr, dtb, uImage
  • Copy the File “dtb” to your Computer
  • decompile
dtc dtb  -O dts -I dtb -o OPi.dts
  • You get a File named “OPi.dts”. Edit the File.
  • Inside the Section “pinctrl@1c20800” (the selected Pin “PA3” is within this range) you have to insert
  w1-pins {
        pins = "PA3";
        function = "gpio_out";
        phandle = <0x2f>;
    	};

and at the end of the file (but before the last bracket!) add:

w1-gpio {
	compatible = "w1-gpio";
	label = "w1-gpio";
	pinctrl-names = "default";
	pinctrl-0 = <0x2f>;
	gpios = <0xa 0x0 0x3 0x6>;
	status = "okay";
	};  

Notice:

  1. phandle: you have to use a hex number following the highest number of phandle used in the file.
  2. gpios: the “0xa” ist the phandle of the used pinctrl, the “0x0” is the used Bank (0 = A…), the “0x3” is the hex number of the used Pin inside the bank, the “0x6” ist the Configuration of the Pin.
  • compile
dtc OPi.dts  -O dtb -I dts -o dtb
  • copy the new “dtb” to the SD Card (overwrite the old “dtb”)
  • Check the output of “dmesg” for (error) messages
...
kern.info kernel: [    7.610839] Driver for 1-wire Dallas network protocol.
...
kern.info kernel: [    7.688174] w1_master_driver w1_bus_master1: Attaching one wire slave 28.0416a43244ff crc be
...

To connect 1Wire Devices to a Host it is necessary to connect a Pullup Resistor of 4.7 kOhm between the Bus Line and the 3.3V VCC Line. On the Internet, other values ​​are given also, here it works well with 4.7kOhm and six DS18B20 Sensors.

It is also possible to operate the 1-Wire Bus with just the Gnd and Bus Lines, with the Sensors deriving power “parasitically” from the Bus Line. For further information, read the datasheet of the device.

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  • Last modified: 2022/02/19 06:21
  • by elux011