1-wire behaviour on Bookworm (2025 Update)

Is this Python code? Python threading cannot currently take full advantage of multiple CPUs, owing to having to serialize all interpreter operations through the “Global Interpreter Lock”.

This is going to be fixed from 3.13 onwards.

No, but AIUI the "right" way to do this is to send the text "trigger" to /sys/bus/w1/devices/w1_bus_master1/therm_bulk_read before reading the values as normal. The trigger causes them all to start a conversion at once, following which the reads all complete immediately once a single conversion time has elapsed.

As a quick hack, try executing the following before reading your sensors...

sudo su <<EOF echo trigger > /sys/bus/w1/devices/w1_bus_master1/therm_bulk_read EOF

It's a C program using posix threads.

I did initially write a Python version using the ThreadPool from multiprocessing.dummy It is only milliseconds slower than the C as the Python threads are able to yield when goes out to the system to read the files in /sys/bus/w1/devices/

That will be very useful for pure Python code. They are making things a bit challenging by deprecating some other things before getting there, which I'll need to sort out before moving on from 3.11.

---druck

On 20/09/2024 11:17, John Aldridge wrote: [Reading ds18b20 sensors in parallel]

Thanks, that seems to works for the first bus, but I get a permission denied when using w1_bus_master2.

---druck

Sorry, I've no idea why that might be :(

Though I do recall the permission checking being a bit odd -- hence the "sudo su" rather than a plain "sudo".

Have you tried 'echo trigger | sudo tee /sys/bus/w1/devices/w1_bus_master1/therm_bulk_read'

Either you’re root or you’re not. There’s no need to say “I am root” twice.

Have you ever tried to manage a Linux system?

There are distinct differences here

Bloody trolls!

Yes, that works for bus 1, but not bus 2 on that Pi 4.

On a Pi Zero 2W with 2 w1 buses, bus 1 gives the Permission denied error and bus 2 succeeds.

On a Pi 3B+ with 4 w1 buses, 1 and 2 succeed, 3 and 4 fail.

Very strange.

---druck

The issue with missing therm_bulk_read for further 1w-busses was raised already in May 2022: