Hello, This is a very interesting topic. I've used ds9490s forever in various topologies wired individually with RJ and never had an issue with finding devices, using maxim's drivers on windows and owfs on Linux. It definitely gets slower as the number of devices increases, but no problems other than that. For cost, I've just implemented a DS2483 on I2C, which is $0.60 vs. $27 for the DS9490. I have not yet tested it extensively. I had assumed that the 2483 would perform better as it doesn't rely on the serial bus and is a newer device. Is this not the case, and what performance difference and limitations should I expect? I'm on raspbian on an RPi.
Thanks, Colin > On Sep 25, 2013, at 16:33, Jan Kandziora <[email protected]> wrote: > > Am 25.09.2013 22:10, schrieb Klaus Weglehner: >> >> There are about 15 DS18B20 mostly in a star topology. > This is near worst-case. You could make it only worse by having some of > these bus-powered. There is no way to have this working reliable. > > If you can't help building a "star" because the sensors are laid out > that way, use lobes instead of single wires so the actual topology is a > bus. Length doesn't matter with onewire, bus topology does. > > >> >> But after a few minutes the Sensors starts disapearing. > First check if your kernel has support for the "w1" sensor bus. That is > onewire the kernel way, mostly for Li-battery control chips found in > some laptops. There is also a "ds2490" module which is accessing a USB > onewire host. The kernel and OWFS get in the way of each other when they > both try do access the adapter. > > You may disable the "ds2490" kernel module by removing/blacklisting it > and keep all the internal onewire hosts (I2C and bitbanging) working > with the w1 kernel module. > > >> >> I would not be surprised if there are transmission errors on the 1-wire >> bus. But why can't the server recover from this? As soon as i restart >> the server, everything is fine again for a few minutes. > That's because the USB adapter is re-initialised when you start > owserver. Disconnect and reconnect it from usb while owserver is > running. Do the onewire devices reappear? (try scanning "uncached" twice > or three times in a row) > > >> Can this be a specific problem of the usb hostadapter which may go away >> by changing to an i2c interface? (I've considered this anyway) >> Or is it a pure 1-Wire bus problem? > The DS9490 usually makes no problems in my networks - dozens at various > locations. > > If you are going for I²C, use two DS2482-800 so you get away from the > star topology. Beware that scanning for chips is very slow with the I²C > adapters, as the host CPU has to control it. The USB adapter has some > algorithm inside to do that independendly of the host CPU. > > In general, I²C is only a bit better than bit-banging onewire with most > host boards, as the I²C host is often realized with bit-banging, too. > Some embedded boards may have a I²C shift register, but that still means > one interrupt each millisecond for just one I²C/Onewire byte. > > > Kind regards > > Jan > > > ------------------------------------------------------------------------------ > October Webinars: Code for Performance > Free Intel webinars can help you accelerate application performance. > Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from > the latest Intel processors and coprocessors. See abstracts and register > > http://pubads.g.doubleclick.net/gampad/clk?id=60133471&iu=/4140/ostg.clktrk > _______________________________________________ > Owfs-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------------ October Webinars: Code for Performance Free Intel webinars can help you accelerate application performance. Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from the latest Intel processors and coprocessors. See abstracts and register > http://pubads.g.doubleclick.net/gampad/clk?id=60133471&iu=/4140/ostg.clktrk _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
