Dnia 3-07-2007 o godz. 23:17 Jean Delvare napisa?(a): > Hi Krzysztof, > > On Sun, 1 Jul 2007 23:37:33 +0200, Krzysztof Helt wrote: > > The analog output has range from 0 to 255. The 0 value is the least value possible but > > it is not 0 voltage on output pin. It simply must be adjusted to the range 1-255 > > to conform with sysfs. I choose this way as the simplest. Another possibility is > > to scale this value when set and displayed from 1-255 (sysfs) to 0-255 (chip) range. > > > > The sysfs 0 value for pwm1 is translated to setting a special bit which cuts off the > > fan power completely (this works on my motherboard and it is given in reference > > design, but I cannot guarantee it is connected this way on all boards). > > I see. Scaling from 1-255 to 0-255 would be counterproductive, but is > it really what you want to do? You say that a register value doesn't > stop the fan, suggesting that the analog output isn't 0V? Do you know > how much it is? For example, if the full analog output is 2.5 V and a > register value of 0 means an output of 1.0 V, then you want to map the > register values 0 to 255 to sysfs values 102 to 255. 0 would stop the > fan, and values from 1 to 101 would behave the same as 102 (i.e. > minimum non-stop speed). See what I mean? > I see, but my explanation was not quite clear/true. According to docs, the THMC50 produces range between 0 and 2.5V. The residual voltage (0 value != 0 V) comes from the external power amplifier. There are 6 example designs of external power amplifier given in the THMC50's datasheet. Most of the are powered by 0 - 12V so they are usually unable to produce the full 0-12V swing (as amplifiers and transistors cannot give output up to power voltage limits). One design (the cheapest) is said to not give full voltage swing by design. That's why they have the fan off bit - to be able to stop the fan. One of designs is powered from +/-12V and this one certainly can produce true 0V output - in such case the 0 value would stop fan and the fan off pin may be left unconnected. As you can see, my driver writes 0 value into the fan speed register along with setting of the fan off bit - to cover both cases. The residual voltage is simple imperfection of analog parts outside the chip and the value of this voltage is as random as the choice of analog elements mounted on motherboards (will vary with production batch change and type of elements e.g. change of supplier). Summary: one knows that 0 value produces 0V at the chip pin and at the same time one knows it is not 0V at the fan pins in most of reference designs (hence the separate fan off bit). Regards, Krzysztof ---------------------------------------------------- Legenda Hip-Hopu w pelnym 9 osobowym skladzie, na jedynym koncercie w Polsce WU-TANG CLAN. 19 lipca 2007 r, godz. 20.00 - Warszawa, klub Stodo?a. http://klik.wp.pl/?adr=http%3A%2F%2Fadv.reklama.wp.pl%2Fas%2Fwutangclan.html&sid=1210
