Subj : Re: 1-wire behaviour on Bookworm
To   : All
From : John Aldridge
Date : Fri Sep 20 2024 11:17:20

In article <vcgrag$gsv0$2@dont-email.me>, news@druck.org.uk says...
>
> After getting another Pi 5, I've moved a Pi 4B running Bookworm in to
> the role taken by a Pi 3B running Bullseye, which is monitoring 6
> ds18b20 sensors, configured as 2 1-wire buses with 3 sensors on each.
>
> With the Pi 3B, I could either read the sensors sequentially taking
> about 0.9s each, or using threads simultaneously in 1.0s. The Pi 4B with
> Bookworm reads the sensors sequentially a shade faster at just over
> 0.8s, but when reading simultaneously, returns 2 after 0.8s, another 2
> after 1.6s and the last two at 2.4s.
>
> Anyone have an explanation for this?

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

--
John

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