Hi Guenter, On Mon, 4 Apr 2011 09:27:26 -0700, Guenter Roeck wrote: > On Sun, Apr 03, 2011 at 08:39:40AM -0400, Jean Delvare wrote: > > On Tue, 22 Mar 2011 20:43:03 -0700, Guenter Roeck wrote: > > > + > > > +curr1_input Current sense input; only if current sensing is enabled > > > + Displayed current assumes 0.001 Ohm current sense > > > + resistor. > > > +curr1_alarm Overcurrent alarm > > > > I'm a little worried about the "assumes 0.001 Ohm (...) resistor". > > Resistors which are external to the chip are normally handled by > > user-space. I understand this is a different case from scaling > > resistor pairs for voltage inputs, but it still feels wrong to assume an > > arbitrary resistor value in the driver. Where does the value come from, > > BTW? I couldn't find it in the datasheet. > > > I have to say the datasheet isn't really easy to read ;). > > Only reason for assuming 0.001 Ohm is that makes adjustments via sensors.conf > easier than, say, 0.005 Ohm or 0.002 Ohm. I guessed so. > The ADC_TO_CURR() calculation is derived from information found in the datasheet, > which I confirmed with the current sense voltage readings on my test board. > > > But I also have to admit that we do not have the needed code in place > > yet to handle it differently. This is similar to the problems described > > in: > > http://www.lm-sensors.org/ticket/2258 > > > > I have another possible implementation idea, I'll post about it > > separately for public discussion. Still on my to-do list, sorry. > Problem is that currents are always measured as voltages, and thus depend on > the series resistor value. I have been hitting the same problem with other > chips supporting current measurements. See the ltc4151 and ltc4261 drivers > for examples. We could imagine chips with an embedded series resistor, so no external resistor is needed. Voltage input scaling has both flavors, and I fail to see why it wouldn't work for current monitoring. > My solution so far is to assume a specific series resistor, and let userspace deal > with adjustments via sensors.conf. > > Another option would might be to add platform data for each of the affected chips. > Would that make sense ? But even then I would need a default value in case there is > no platform data. You could make platform data mandatory for these chips, or at least for their current monitoring feature. > [ ... ] > > > > I couldn't find in the datasheet any guarantee that the MSB and the LSB > > belong to the same measurement, but I admit I didn't read it too > > carefully. Is this the case? > > > No, or at least I did not find it either. Turns out, however, that I can use > 16 bit reads since the chip auto-increments the address. I'll do that instead. I was curious about that, but not seeing any mention of it in the datasheet (which otherwise looks quite complete) I thought it wasn't supported. -- Jean Delvare _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
