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Include dynamic DT loading, hw pull-up requirement

This commit is contained in:
Tim Small 2017-07-11 16:02:42 +01:00
parent c19a7a2fd2
commit de4401fb45
1 changed files with 11 additions and 1 deletions
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12
src/en/overlay/iface-1wire.md
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@ -31,8 +31,18 @@ Alternatively you can enable the one-wire interface on demand using raspi-config
sudo modprobe w1-gpio
```
once either of the steps above has been performed, you can list the devices your Raspberry Pi can probe via (by default) BCM4, like so:
Newer kernels (4.9.28 and later) allow you to use dynamic overlay loading instead, including creating multiple 1-Wire busses to be used at the same time:
```
sudo dtoverlay w1-gpio gpiopin=4 pullup=0 # header pin 7
sudo dtoverlay w1-gpio gpiopin=17 pullup=0 # header pin 11
sudo dtoverlay w1-gpio gpiopin=27 pullup=0 # header pin 13
```
once any of the steps above have been performed, and discovery is complete you can list the devices that your Raspberry Pi has discovered via all 1-Wire busses (by default BCM4), like so:
```
ls /sys/bus/w1/devices/
```
n.b. Using w1-gpio on the Raspberry Pi typically needs a 4.7 kΩ pull-up resistor connected between the GPIO pin and a 3.3v supply (e.g. header pin 1 or 17). Other means of connecting 1-Wire devices to the Raspberry Pi are also possible, such as using i2c to 1-Wire bridge chips.