OWFS does use the simultaneous conversion technique, if possible. My understanding is that simultaneous does not work in passive power mode.
There are some subtleties: 1. The simultaneous is bus-specific. I.e., each bus-master is sent a simultaneous request and if there are no passive sensors, the match-rom/convert is done. 2. The time of the last simultaneous is recorded, and all cached temperatures are dumped. 3. When a temperature is then requested, if there is a valid simultaneous for that bus, we pause until it's a full conversion time, then read the temperature and store it in the cache with the remaining time. 4. A request for uncached works as normal and doesn't interfere with the rest of the temperatures. You know there are alternative temperature sensors that are much faster, like the DS2438 or the new EDS0071 with RTD or a thermocouple or any of the BAE devices, or the Hobby Boards UVI device. Paul Alfille On Sat, Feb 5, 2011 at 9:43 AM, Roberto Spadim <[email protected]> wrote: > maybe you should use simultaneous + cached read > since it can put all temperatures in cache, while you just read 1 temperature > check source code, but i think that's something like it > > 2011/2/5 Roberto Spadim <[email protected]>: >> i didn't read the code about this skip rom command in owfs, but i >> think it's just a bit (a file) to change from 0 to 1 >> and all new temperatures will be read as simultaneous >> the problem is >> if owfs just read one file, how could you use this function? you >> should read 100 files at once, but it doesn't exists (i think) >> >> 2011/2/5 Mick Sulley <[email protected]>: >>> Yes I have seen the 85 degree situation, it happens sometimes if you run >>> in parasitic mode and do not ground the VDD line, but sometimes it seems >>> to run happily like that. >>> >>> I see the reference in the spec sheet to issuing a Skip ROM command, but >>> I have no idea how to do that using pyowfs. I guess I need to read a >>> bit deeper into basic owfs documentation. >>> >>> Thanks >>> Mick >>> >>> On Sat, 2011-02-05 at 03:29 +0100, patyrk wrote: >>>> Dnia 2011-02-04, pią o godzinie 23:34 -0200, Roberto Spadim pisze: >>>> > i never used simultaneous... >>>> > but ds18b20 and ds18s20 sometime have a problem (maybe low power or >>>> > problem on wire, i never founded why) >>>> > it restart internal cpu (ds1820) >>>> > and send 85 degree (i don't remember but it's a fixed value) >>>> > if you get that value, you need read more two times to get the real value >>>> > i think simultaneous read will make it more problematic... >>>> >>>> Just read the ds18b20 specs and found this (page 11) >>>> http://datasheets.maxim-ic.com/en/ds/DS18B20.pdf >>>> SKIP ROM [CCh] >>>> The master can use this command to address all devices on the bus >>>> simultaneously without sending out >>>> any ROM code information. For example, the master can make all DS18B20s >>>> on the bus perform >>>> simultaneous temperature conversions by issuing a Skip ROM command >>>> followed by a Convert T [44h] >>>> command. >>>> >>>> So it should be possible to make conversion and the read all >>>> scratchpads? Is should be much faster. The specs doesn't mention that >>>> ds18b20 can't be in parasite mode. I think that just blocking the bus 1 >>>> second will give enough time for conversion to take place. >>>> >>>> Now I don't see any performance increase when invoking simultaneous >>>> before temp. read. >>>> >>>> -- >>>> P4trykx >>>> >>>> > >>>> > >>>> > 2011/2/4 patyrk <[email protected]>: >>>> > > Dnia 2011-02-05, sob o godzinie 01:10 +0000, Mick Sulley pisze: >>>> > >> My sensors are powered, the temperature sensors are a mix of DS18B20 >>>> > >> and >>>> > >> DS18S20, I just used DS1820 as a generic term. >>>> > >> >>>> > >> Is there a way to use simultaneous conversion with pyowfs? >>>> > > I don't know pyowfs >>>> > > but when mounted by owfs there is a >>>> > > >>>> > > /mnt/owfs/simultaneous/temperature >>>> > > >>>> > > file and I suspect writing 1 to this file trigers the conversion signal >>>> > > >>>> > > >>>> > > >>>> > > -- >>>> > > P4trykx >>>> > > >>>> > > >>> >>> >>> ------------------------------------------------------------------------------ >>> The modern datacenter depends on network connectivity to access resources >>> and provide services. The best practices for maximizing a physical server's >>> connectivity to a physical network are well understood - see how these >>> rules translate into the virtual world? >>> http://p.sf.net/sfu/oracle-sfdevnlfb >>> _______________________________________________ >>> Owfs-developers mailing list >>> [email protected] >>> https://lists.sourceforge.net/lists/listinfo/owfs-developers >>> >> >> >> >> -- >> Roberto Spadim >> Spadim Technology / SPAEmpresarial >> > > > > -- > Roberto Spadim > Spadim Technology / SPAEmpresarial > > ------------------------------------------------------------------------------ > The modern datacenter depends on network connectivity to access resources > and provide services. The best practices for maximizing a physical server's > connectivity to a physical network are well understood - see how these > rules translate into the virtual world? > http://p.sf.net/sfu/oracle-sfdevnlfb > _______________________________________________ > Owfs-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/owfs-developers > ------------------------------------------------------------------------------ The modern datacenter depends on network connectivity to access resources and provide services. The best practices for maximizing a physical server's connectivity to a physical network are well understood - see how these rules translate into the virtual world? http://p.sf.net/sfu/oracle-sfdevnlfb _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
