hi Guil,
The fastest conversion time for ds18b20 is 93,75ms with 9 bit resolution; I
don't know where you found 10ms...
If you concern is to minimise duration on polling temperatures and if all
your ds18b20 are powered, you may issue a simultaneous temperature
conversion command, do something else for 750ms, then read the temperatures
as usual.
The simultaneous command instruct all temp sensors on the branch to start
the conversion. once the conversion is known (max duration is 750ms for
12bit) to be finished, the next readings simply (should) read prepared data.
in you case, simultaneous conversion is triggered with:
owwrite -s 4444 /uncached/sw3/aux/simultaneous/temperature 1
not sure however that this behavior is working as expected when dealing with
a ds2409 in between.
Pascal
>
2011/1/23 Guil Barros <[email protected]>
> I am doing a number of reads with owget on individual DS18B20's and
> DS2438's and not quite getting the performance I expect:
> # time ./owfs/bin/
> owget -s 4444 /uncached/sw3/aux/Hallway/temperature
> 18.9375
> real 0m 0.38s
> user 0m 0.00s
> sys 0m 0.01s
>
> The actual convert_t from the datasheet should take only 10ms. What
> can I do to speed this up? (yes, that DS2409 port is already the
> active one).
>
> I have also noticed something similar for DS18B20 fasttemp reads which
> should take 95ms:
> # time ./owfs/bin/
> owget -s 4444 /uncached/sw1/main/Attic/fasttemp
> -1
> real 0m 0.84s
> user 0m 0.00s
> sys 0m 0.00s
>
> I assume this is at least partially overhead related to the owserver
> comms, is there a better way to handle multiple device access with the
> owshell commands? Anything I can do to speed things up otherwise?
>
> Thanks,
> -Guil
>
>
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--
Pascal
www.brain4home.eu
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