On Mon, Oct 28, 2013 at 11:48:46AM -0700, Chris Verges wrote: > On Mon, Oct 28, 2013 at 10:35:18AM -0700, Guenter Roeck wrote: > > On Mon, Oct 28, 2013 at 09:05:05AM -0700, Chris Verges wrote: > > > The LM73 datasheet recommends resetting the sensor at power-up to > > > avoid certain VDD ramp-up problems. The full sequence and rationale > > > is described in the LM73 datasheet, May 2009 revision, page 19, > > > section "Power Supply Ramp-Up Considerations." > > > > common assumption is that the chip is enabled and pre-configured by > > the BIOS or ROMMON. If so, this code is unnecessary and just adds > > 100+ ms to the system boot time for each LM73 sensor. I don't think > > that would be a good idea. > > > > The datasheet says "... In systems where there is a large amount of > > capacitance on the VDD node, the LM73 power supply ramp-up time can > > become excessively long", which is defined as "A linear power-on-ramp > > of less than 0.7V/msec and an exponential ramp with an RC time > > constant of more than 1.25 msec is categorized as a slow power-supply > > ramp". The soft-reset is only required if this is the case. > > > > Are there indications that this condition is actually seen on real > > hardware, and not taken care of by the BIOS/ROMMON? > > Yes, I encountered this problem on an embedded system and discovered the > note in the datasheet as part of the debugging of that problem. The > LM73 started returning random, sporadic temperature readings as a result > of VDD being ramped too slowly. The app note's tone makes the > recommendation sound like the TI-preferred methodology of device > initialization for guaranteed behavior, and so modifying the probe() > directly seemed like a better choice than relying on the user to know to > enable this functionality via module params, platform data, or > devicetree properties. > It is not acceptable to affect everyone because one embedded system vendor violates voltage ramp-up time for this chip. The embedded system should have its well defined configuration, and support devicetree and/or platform initialization code. So adding it through one or both of those methods should be straightforward. The (end-)user should not have to be involved; the company providing the system should. Thanks, Guenter _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
