Hi all experts,
so I just made some tests on a ARM 400MHz with I2C hardware driver DS2482
getting temperature from a DS18B20.
For me it's a surprise:
I've written a small C-program using the owcapi (see attached .c and
Makefile) http://old.nabble.com/file/p32244690/testowfs.c testowfs.c
http://old.nabble.com/file/p32244690/Makefile Makefile
I started the owcapi program without any owserver to read the uncached temp
10-times:
time ./testowfs uncached/28.018ACE010000.D8/temperature9 10
and counted average 670ms per 9-bit measurement, so far away from the 93ms
the conversion in the device costs.
A 12-bit measurement took 1180ms in average, so not much slower.
Later I started owserver and an owshell program 10 times to read the
uncached temp:
time for i in {1..10}; do /opt/owfs/bin/owread
/uncached/28.018ACE010000.D8/temperature9; done
and counted 1070ms per measurement, so you are right, this is a little bit
slower
An owfs call I can't measure at the moment, due to problems with the fuse
(other thread)
Achim
Paul Alfille-2 wrote:
>
> In all cases, actual 1-wire communication is the slowest part of the
> process. Each bit transmitted is 62usec
>
> The owshell approach requires a new process for every 1-wire call. Linux
> processes are supposed to fairly light but it's probably the slowest
> approach. And getting to that data in a C program isn't convenient.
>
> owfs should be pretty fast, the actual "filesystem" part of it does
> require
> a pass through the kernel for each transaction, but the fuse interface is
> pure subroutine calls. Getting to the data in C (or any language) is very
> convenient -- file access is natural.
>
> The owserver approach requires network communication. Again pretty fast.
>
> If you really want the lowest latency, use owcapi in your C program. There
> is no pass through the network or filesystem and the interface is simple.
>
> If other processes need to access the 1-wire data at the same time, you
> need
> owserver or the filesystem. If they need to access remotely, you need
> owserver. All the methods, including owcapi, can access owserver.
>
> All the methods are pretty fast and I'd choose the simplest approach for
> development.
>
> Alias should be pretty fast, it's just a binary table lookup from memory.
>
> Paul Alfille
>
> On Wed, Aug 10, 2011 at 4:11 AM, ekgnkb3d <[email protected]> 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:
>>
>> The convenience of all the different owfs client technologies is great
>> (thanks to the developers for this amazing piece of code!!!), assuming
>> there
>> is not much difference in adapting my C-coded application. Which one of
>> the
>> following give the fastest access, creating the minimum CPU load:
>>
>> - owfs, accessing files in directories via fuse
>> - owshell, calling shell commands via local owserver
>> - owserver, adding code to my C-application acting as TCP client
>>
>> Or maybe it is not worth a discussion and all mentioned possibilities
>> have
>> almost the same speed/load?
>>
>> Another questions:
>> Does using alias slowing down the access??
>>
>> thanks a lot
>> Achim
>> --
>> View this message in context:
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>>
>>
>>
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