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In article <vckmfh$17vkc$2@dont-email.me>, news@druck.org.uk says...
On 20/09/2024 11:17, John Aldridge wrote:
[Reading ds18b20 sensors in parallel]
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
Thanks, that seems to works for the first bus, but I get a permission
denied when using w1_bus_master2.
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".
On Sun, 22 Sep 2024 11:53:07 +0100, John Aldridge wrote:
Though I do recall the permission checking being a bit odd -- hence the
"sudo su" rather than a plain "sudo".
Either you’re root or you’re not. There’s no need to say “I am root”
twice.
Though I do recall the permission checking being a bit odd -- hence the
"sudo su" rather than a plain "sudo".
On 22/09/2024 at 11:53, John Aldridge wrote:
In article <vckmfh$17vkc$2@dont-email.me>, news@druck.org.uk says...
On 20/09/2024 11:17, John Aldridge wrote:
[Reading ds18b20 sensors in parallel]
sudo su <<EOF
echo trigger > /sys/bus/w1/devices/w1_bus_master1/therm_bulk_read
EOF
Have you tried
'echo trigger | sudo tee /sys/bus/w1/devices/w1_bus_master1/therm_bulk_read'
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.
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