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How to Use Simultaneous

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	How to Use Simultaneous by Doug Collinge-2 :: Rate this Message: \| View Threaded \| Show Only this Message I'm writing myself a little Python code here and trying to use 'simultaneous' but getting results that are inconsistent with my understanding. I have multiple DS1820 devices on a bus. They are all powered devices. I want to simultaneously convert them all, wait, then read them all. I'm expecting that when I go to read them, since I have signalled a simultaneous conversion, that they will all be already converted and ready to send their data, .except perhaps the first one if I haven't waited long enough for the conversion. I'm writing a 1 to '/simultaneous', processing some other stuff, then reading them all. If I read from '/uncached/temperature' it takes 600-some-odd milliseconds to read each one, which sounds like they are all doing a fresh conversion. If I read from '/temperature' then I get them read in much faster but I don't get a fresh conversion each time. What I want is for writing to '/simultaneous' to always kick off a fresh conversion of all the devices so that I always get a new sample when I read them, and never take data out of the cache. How can I accomplish this? ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers
	Re: How to Use Simultaneous by Paul Alfille-2 :: Rate this Message: \| View Threaded \| Show Only this Message Your second use i the correct one. Write "1" to simultaneous to trigger a conversion. That also clears the cache. A normal read will read immeadiately the already measured temperature ready in the device. Paul Alfille On Sat, Jul 12, 2008 at 8:28 PM, Doug Collinge <doug.collinge@...> wrote: I'm writing myself a little Python code here and trying to use 'simultaneous' but getting results that are inconsistent with my understanding. I have multiple DS1820 devices on a bus. They are all powered devices. I want to simultaneously convert them all, wait, then read them all. I'm expecting that when I go to read them, since I have signalled a simultaneous conversion, that they will all be already converted and ready to send their data, .except perhaps the first one if I haven't waited long enough for the conversion. I'm writing a 1 to '/simultaneous', processing some other stuff, then reading them all. If I read from '/uncached/temperature' it takes 600-some-odd milliseconds to read each one, which sounds like they are all doing a fresh conversion. If I read from '/temperature' then I get them read in much faster but I don't get a fresh conversion each time. What I want is for writing to '/simultaneous' to always kick off a fresh conversion of all the devices so that I always get a new sample when I read them, and never take data out of the cache. How can I accomplish this? ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers
	Re: How to Use Simultaneous by Doug Collinge-2 :: Rate this Message: \| View Threaded \| Show Only this Message Ah, writing to '/simultaneous' actually seems to wait for the conversion to complete. I didn't realize that. I'd better check the code here ... ... Yes, it does poll for completion of the conversion. I think that explains a few things. I'll go back to the drawing board with this new info. Is there anywhere where this behaviour of '/simultaneous/temperature' is documented? I mean, clears cache, polls for conversion. On Sat, Jul 12, 2008 at 20:29, Paul Alfille <paul.alfille@...> wrote: Your second use i the correct one. Write "1" to simultaneous to trigger a conversion. That also clears the cache. A normal read will read immeadiately the already measured temperature ready in the device. Paul Alfille On Sat, Jul 12, 2008 at 8:28 PM, Doug Collinge <doug.collinge@...> wrote: I'm writing myself a little Python code here and trying to use 'simultaneous' but getting results that are inconsistent with my understanding. I have multiple DS1820 devices on a bus. They are all powered devices. I want to simultaneously convert them all, wait, then read them all. I'm expecting that when I go to read them, since I have signalled a simultaneous conversion, that they will all be already converted and ready to send their data, .except perhaps the first one if I haven't waited long enough for the conversion. I'm writing a 1 to '/simultaneous', processing some other stuff, then reading them all. If I read from '/uncached/temperature' it takes 600-some-odd milliseconds to read each one, which sounds like they are all doing a fresh conversion. If I read from '/temperature' then I get them read in much faster but I don't get a fresh conversion each time. What I want is for writing to '/simultaneous' to always kick off a fresh conversion of all the devices so that I always get a new sample when I read them, and never take data out of the cache. How can I accomplish this? ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers
	Re: How to Use Simultaneous by Paul Alfille-2 :: Rate this Message: \| View Threaded \| Show Only this Message Documented? Apparently not well. This note should help: http://www.mail-archive.com/owfs-developers@.../msg02524.html On Sun, Jul 13, 2008 at 3:25 AM, Doug Collinge <doug.collinge@...> wrote: Ah, writing to '/simultaneous' actually seems to wait for the conversion to complete. I didn't realize that. I'd better check the code here ... ... Yes, it does poll for completion of the conversion. I think that explains a few things. I'll go back to the drawing board with this new info. Is there anywhere where this behaviour of '/simultaneous/temperature' is documented? I mean, clears cache, polls for conversion. ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers
	Re: How to Use Simultaneous by Doug Collinge-2 :: Rate this Message: \| View Threaded \| Show Only this Message I spent a little time reading the thread you referenced and going back to the datasheets. You said, David Lissiuk pointed out that my assumptions about the DS18x20's behavior were incorrect. This may explain the rare problems with conversion, especially when powered and unpowered sensors were mixed. Basicallly, during powered temperature conversion, the bus is still unusable because the data line is help low until a temperature is ready. I suspect this is an early design decision, since the DS2450 will free the bus for powered voltage conversions if you issue a reset. Here is what the datasheet says: If the DS18S20 is powered by an external supply, the master can issue "read-time slots" (see the 1-Wire Bus System section) after the Convert T command and the DS18S20 will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion is done. It's not completely unambiguous but I conclude that the problem is that, once the simultaneous conversion has been issued, all thermometers think they are selected and respond to reads with a conversion status, low if still converting and high if finished. This way they are all wire-ored together and the result tells us if any of them are still converting. So yes, apparently you can't use the bus during this interval unless there is some way of deselecting the active thermometers without disturbing the conversion in progress. I don't think the datasheet has anything to say about that. I mentioned the documentation because I would be happy to update the documentation if you would tell me where you think the updates should go. On Sun, Jul 13, 2008 at 03:34, Paul Alfille <paul.alfille@...> wrote: Documented? Apparently not well. This note should help: http://www.mail-archive.com/owfs-developers@.../msg02524.html On Sun, Jul 13, 2008 at 3:25 AM, Doug Collinge <doug.collinge@...> wrote: Ah, writing to '/simultaneous' actually seems to wait for the conversion to complete. I didn't realize that. I'd better check the code here ... ... Yes, it does poll for completion of the conversion. I think that explains a few things. I'll go back to the drawing board with this new info. Is there anywhere where this behaviour of '/simultaneous/temperature' is documented? I mean, clears cache, polls for conversion. ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Owfs-developers mailing list Owfs-developers@... https://lists.sourceforge.net/lists/listinfo/owfs-developers