Achim:
On 8/10/2011 04:11, ekgnkb3d wrote:
Hello everybody,
I'm new to this forum and shortly want to introduce myself:
During my tests with 1-Wire for a hot-water controller, I used the Maxim
Public Domain Kit. But due to some limitations I try to switch to owfs now.
My biggest fear at owfs is a low performance causing high load at my CPU
which is with 400MHz and ARM9 very limited... I'm using an hardware I2C
channel /dev/i2c-0 with DS2482-100. The aim is to have a closed loop
controlling rate of max 250ms for 4 DS18B20 temp sensing plus DS2408 dac. So
therefore my (newbie) questions:
Your requirement includes a "closed loop" control and you imply a need
for rapid and accurate data from the sensors. You specify a max of
250ms to read 4 DS18B20 sensors. Reading data from OWFS is one thing.
Having data from a given sensor that is fresh within the 250ms you
specify is another. eg: why read every 250 ms if the data is around 1
second old? (at low sensor count, I believe OWFS can issue a convert
and post an update to all temperature sensors every 1 second).
There are some potential complications to point out in any approach, but
I will include these related to OWFS as I understand them:
1. The conversion time for the DS18B20 varies depending upon
resolution. Assuming your control requires the highest resolution (12
bit) the best conversion time you will get is 1000 ms.
2. OWFS can perform a "simultaneous" conversion on a given net
(simultaneous=1). This means all temperature sensors on a bus will
convert with a single one wire API call. But to take advantage of this
you must be certain that all four sensors are on the same physical net.
3. I assume that a simultaneous conversion, or any OWFS temperature
conversion, is done for the highest resolution (Paul might weigh-in
here). As such, it can be assumed that any conversion of DS18B20's will
take about 1 second to complete.
I would agree with Paul, and having some experience now with owcapi, it
is indeed the best way to go if your requirements are otherwise met.
/m
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