On Thu, Jan 28, 2010 at 2:28 PM, Pascal Baerten <[email protected]>wrote:
> Hi,
>
> I'm also concerned by responsiveness of temp readings.
> Here my experience:
> First, the ds18b20 chips are not continuously converting temperature
> themselves , they only start a measurement when they receive a convertT
> command from the master. The conversion require up to 750ms for at 12 bits
> resolution and consume power.
> So after issuing a convertT command (for example with "echo 1 >
> owpath/simultaneous/temperature"), you have to wait the end of conversion
> before the result is availlable.
>
It seems that the 750 msec is optimistic, despite what the datasheet says.
Most 1-wire programs (digitemp, public domain kit) use 1 second. The number
of errors (85C readings) improved when we made the change to the longer
conversion times.
Powered vs not powered chips:
> The ds18b20 are able to work from externally powered source or from
> parasite power. It is important to remember that using parasite power
> require the master to maintain strong pullup on DQ during whole conversion
> process and thus avoiding any bus activities during the conversion.
> To avoid locking the bus by the strong pullup, you have to power externally
> *all* temperature chips.
>
> I've verified that when ds18b20 chips are powered, they continue conversion
> even if the master communicate to other devices on the network.
>
That's very interesting. I had originally designed the system that way, (bus
communication allowed during powered conversions) but there was contrary
information as documented here:
http://article.gmane.org/gmane.comp.file-systems.owfs.devel/3200/match=powered+temperature+conversion
> Owfs *should** *allow bus master to accept bus communication to other
> devices during conversion.
>
>
It would be easy to do (since it's the old behavior, and we specifically
lock the bus and the slave separately to allow independent access), but I'm
not sure if it actually works in 1-wire.
> This is the case on my particular configuration based on a DS2482-800
> master.
> Here is a simple test done in php/ownet on my nslu2 with latest svn with
> all ds18b20 present powered.
> The last value is the measured duration in seconds that the command needed
> to finish.
>
> Reading directly temperature after a simultaneous command force the master
> to wait end of conversion before returning the result. -> we lost precious
> time (1.20 second) waiting conversion.
>
>> connect to ownet 0.00356793403625
>> set /bus.3/simultaneous/temperature=1 0.0554330348969
>> read temperature for /uncached/bus.3/28.D1729B010000/temperature =
>> 3.1875 *1.20092391968*
>>
> The next lines show that bus activity is possible without delays during
> conversion:
>
>> set /bus.3/simultaneous/temperature=1 0.0292129516602
>> set /bus.3/05.878C33000000/PIO 1 0.245070934296
>> read /uncached/bus.3/05.878C33000000/sensed=0 0.104848861694
>> set /bus.3/05.878C33000000/PIO 0 0.146059989929
>> read /uncached/bus.3/05.878C33000000/sensed=1 0.100878000259
>> ...
>>
> after at least 0.7 second, converted temp could be read without delay
>
>> read temperature for /uncached/bus.3/28.D1729B010000/temperature =
>> 3.125 *0.182569980621*
>> done
>>
>
>
> However, this work correctly only on specific DS2482-800, for any other
> adapter, the bus remain locked for the duration of conversion.
>
>
Right. Independent bus masters are be handled completely separately. The
DS2482-800 is essentially 8 independent bus masters (except that some global
settings apply to them all.)
> here the same test done on i386 platform with an ds2490 usb master.
>
>> connect to ownet 0.00307703018188
>> temperature for /bus.0/28.2DDB01020000/temperature =
>> 20.4375 0.767754077911
>>
>
>
>> set /bus.0/simultaneous/temperature=1 *0.658293962479 *(simultaneous
>> blocks on poll_convert)
>> set /bus.0/12.B31F5F000000/PIO.B=1 0.174618005753
>> read /uncached/bus.0/12.B31F5F000000/sensed.B=0 0.0654580593109
>> set /bus.0/12.B31F5F000000/PIO.B=0 0.100481033325
>> read /uncached/bus.0/12.B31F5F000000/sensed.B=1 0.0521919727325
>> ...
>> temperature for /bus.0/uncached/28.2DDB01020000/temperature =
>> 20.5 0.113564968109
>> done
>>
>
> Paul,
> in ow_simultaneous.c, the function FS_w_convert_temp() could handle other
> adapter in the same way than DS2482-800. However this should be conditional
> to whether all temp chips are powered or not. However I don't know how to
> verify easily if this conditions is met.
>
>
It gets complicated. Clearly we could have a command line switch ( but that
goes against the simple configuration aesthetic). We could ask each chip,
and remember the answer (which would work well as long as new slaves don't
pop up). It's possible that we could use the same technique used for
simultaneous conversion -- ask all the bus, but I'd have to investigate
whether the command codes collide with other chip designs.
>
> Pascal
>
>
>
> 2010/1/28 Sophana K <[email protected]>
>
> When you "set the simultaneous convert", do you mean you write 1 to
>> the top/simulaneous/temperature?
>>
>> something like this?:
>> echo 1 > simultaneous/temperature
>> cat 1F.C4DC03000000/aux/28.C4027E010000/temperature
>> cat 1F.C4DC03000000/aux/28.0D337E010000/temperature
>>
>> This doesn't work for me, it is slow.
>>
>> Are you driving the "local" simultaneous files (like
>> 1F.C4DC03000000/aux/simultaneous/temperature)
>>
>> What version of owfs are you using?
>> Do you think I should upgrade?
>>
>> I'm also running a hvac system which currently has period of about 20
>> seconds. Which is still ok for now.
>> But I'm going to extend it with about 10 more sensors, and I would
>> like it to be more reactive when driving the 4 way valves.
>>
>> What platform are you using? I'm considering upgrading to an low power
>> intel atom (or d510) based PC or maybe dedicating a sheeva plug for
>> the hvac. My current router (asus wl500g deluxe) doesn't have a real
>> time clock so I need the internet at boot time just to get the time
>> for my hvac system to work.
>>
>> Thanks for your help
>>
>> On Wed, Jan 27, 2010 at 6:30 PM, Jerry Scharf
>> <[email protected]> wrote:
>> > Sophana,
>> >
>> > First, I drive my sensors from python through owserver, so a simple
>> > example probably won't help you. I don't think that "on their own
>> > segment" is enough because the sensor can't know that, but this is
>> > beyond my level of knowledge about 1-wire.
>> >
>> > What I do is set the simultaneous convert and then read the sensors
>> > sequentially. The master can only do one thing at at time, so I didn't
>> > see much value in doing any threading for my simple problem. The timing
>> > definitely shows that they are not doing the conversion at read time.
>> > It's easy to compare by just skipping the simultaneous and doing the
>> > sequential read.
>> >
>> > I'm running a HVAC system, so readings every 30 seconds is fine. Not
>> > what I would call a high speed operation.
>> >
>> > hope that helps,
>> > jerry
>> >
>> > Sophana K wrote:
>> >> Hi
>> >>
>> >> I made the tests on powered sensors.
>> >> Some other sensors are not powered but they are "alone" on their own
>> >> hub segments.
>> >> You don't need to write to the simultaneous/temperature file?
>> >> Just do parallel access to owserver?
>> >> Or do you do both?
>> >> Can you give an example of access sequence you are doing?
>> >> Does owfs on top of owserver limit parallel access to the values?
>> >> Should I try directly with threads inside my python program to access
>> >> owserver in parallel?
>> >>
>> >> Thanks
>> >>
>> >> On Wed, Jan 27, 2010 at 5:10 PM, Jerry Scharf
>> >> <[email protected]> wrote:
>> >>> Sophana,
>> >>>
>> >>> I am sure this works. I have a hub (not a switch) and do simultaneous
>> >>> reads for my 30+ temp sensors. Do you have separate power or are you
>> >>> running in parasitic mode. I am fairly certain you can not do
>> >>> simultaneous reads with parasitic power.
>> >>>
>> >>> jerry
>> >>>
>> >>> Sophana K wrote:
>> >>>> On Mon, Jan 11, 2010 at 4:35 PM, Paul Alfille <
>> [email protected]> wrote:
>> >>>>
>> >>>>> It's easy to do if the segments are on different bus masters. Just
>> read in a
>> >>>>> different thread or program since only the bus master is locked. An
>> >>>>> asynchronous read property for temperature is also possible.
>> >>>> I tried this, but it doesn't seem to work.
>> >>>> I made the test through owfs on top of owserver -u with a small
>> script
>> >>>> making simultaneous accesses to different sensors. It is as slow as
>> >>>> reading the sensors sequentialy.
>> >>>> Are you sure about this feature?
>> >>>>
>> >>>>
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>
>
> --
> Pascal
>
>
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