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.
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.
Owfs *should** *allow bus master to accept bus communication to other
devices during conversion.
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.
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.
Pascal
2010/1/28 Sophana K <sophan...@gmail.com>
> 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
> <sch...@lagunawayconsulting.com> 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
> >> <sch...@lagunawayconsulting.com> 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 <paul.alfi...@gmail.com>
> 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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