Hi all: I've been reporting for a while that alarming was not working with DS18B20 temperature chips. Today we have finally gotten the traces and compared to the Dallas data sheets to figure out exactly why they're not working.
Thanks to the relatively new bus traffic debug feature, we were able to get this. It appears that all the alarming setup stuff works. We did find a bug in the reading of the alarm values: owfs only reads from the scratchpad; it does NOT first copy from the alarm EEPROM to the scratchpad. Therefore, unless you just set the alarm value, the value OWFS reads out is actually not correct. After setting Thigh and Tlow, we entered into a loop of echo "1" > simultaneous/temperature followed by a ls of the alarm directory. In our case, the temperature chip always shows up in the alarm directory, even when it should not. However, if we cat fasttemp for a chip, it will disappear from the alarm directory. Today's research revealed that the issue is that OWFS is NOT handling the bus powered situation correctly. It looks like the alarming function would work perfectly if all of our DS18B20s were externally powered. However, we run all of ours parasitic. I suspect that some logic needs to be added to OWFS to "know" if it has at least one bus-powered chip (there's a simple OW command that can be run to do this, IIRC), and then it would need to execute the strong pullup after a convert command. Thanks! (BTW: our test version of OWFS 2.8p3 with owtraffic, used with the dallas USB bus master blows up randomly with cannot reconnect errors; 2.8p2 worked stably. We did not check 2.8p4.) --Jim CASAS Lab Manager @ Washington State University ------------------------------------------------------------------------------ Learn how Oracle Real Application Clusters (RAC) One Node allows customers to consolidate database storage, standardize their database environment, and, should the need arise, upgrade to a full multi-node Oracle RAC database without downtime or disruption http://p.sf.net/sfu/oracle-sfdevnl _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
