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Date: Mon, 21 Jan 2008 17:15:57 -0600 From: David Fries <david@...es.net> To: Evgeniy Polyakov <johnpol@....mipt.ru> Cc: linux-kernel@...r.kernel.org Subject: W1: w1_slave units, standardize 1C or .001C? Break API The ds18b20 one wire temperature sensor conversion routine is returning the units in degrees C while the ds1820 (ds18s20) is returning it in .001 degrees C. 20C vs 20312C. Once you know the units I'm liking the latter as it gives a higher precision. Time to break user applications so the driver can give the temperature in the same units for both sensors. I only have the ds18b20 sensor model. Here is the current output from the sys file for this sensor. /sys/devices/w1_bus_master1/28-0000000e84a2/w1_slave 45 01 4b 46 7f ff 0b 10 84 : crc=84 YES 45 01 4b 46 7f ff 0b 10 84 t=20 I ran the example data from the specification for the ds1820 through it's conversion routine and found that t= was 1000 times the value. What should the displayed units be? This is the same ds18b20 conversion *1000. Is everyone ok or is any objecting to .001 degrees C for the units? Patch will follow. The .001 C does truncate one bit of precision from the ds18b20 by the way. 45 01 4b 46 7f ff 0b 10 84 : crc=84 YES 45 01 4b 46 7f ff 0b 10 84 t=20312 -- David Fries <david@...es.net> http://fries.net/~david/ (PGP encryption key available) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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