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Message-ID: <CAOMwXhMRtNaxtA7=cc7ur_Qf3iwZAHi=sk-Ujp=hggGA1O5u+Q@mail.gmail.com> Date: Mon, 10 Mar 2014 13:50:01 +0000 From: Laszlo Papp <lpapp@....org> To: Guenter Roeck <linux@...ck-us.net> Cc: LKML <linux-kernel@...r.kernel.org>, lm-sensors@...sensors.org Subject: Re: [lm-sensors] Tachometer speed returned rather than absolute fan speed? On Mon, Mar 10, 2014 at 1:26 PM, Guenter Roeck <linux@...ck-us.net> wrote: > On 03/10/2014 02:59 AM, Laszlo Papp wrote: >>> >>> The reason is (most likely) that your fan input does not have a pull-up >>> resistor. Per datasheet, the fan inputs need a 10kOhm pull-up resistor. I >>> confirmed this with my test board - with the pull-up resistor, inputs read >>> 0, Without pull-up, the reported value is 1, which translates to 30 RPM. You >>> might also need the 10 uF capacitor on the FB pin. >> >> >> We have both of them in place as per requirement for the chip as far >> as I understand the datasheet. The circuit would not work properly >> without it. >>> >>> sudo i2cdump -y -f 1 0x48 >>> No size specified (using byte-data access) >>> 0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef >>> 00: 00 00 0a 0a ff ff 00 00 00 00 00 00 01 01 00 00 ..??........??.. >>> 10: 01 01 01 01 1f 1f 02 02 91 91 91 91 91 91 91 91 ???????????????? >>> 20: 00 00 0a 0a ff ff 00 00 00 00 00 00 01 01 00 00 ..??........??.. >> >> >> /usr/sbin/i2cdump -y -f 1 0x48 >> No size specified (using byte-data access) >> 0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef >> 00: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> 10: 09 09 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> 20: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> 30: 09 09 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> 40: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> 50: 08 08 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> 60: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> 70: 08 08 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> 80: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> 90: 08 08 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> a0: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> b0: 08 08 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> c0: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> d0: 08 08 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> e0: 00 00 3a 3a fc fc b4 b4 00 00 00 00 01 01 01 01 ..::????....???? >> f0: 08 08 01 01 1c 1c 02 02 91 91 91 91 91 91 91 91 ???????????????? >> >>> groeck@...ktop:~$ sensors max6651-i2c-1-48 >>> max6651-i2c-1-48 >>> Adapter: i2c-diolan-u2c at bus 003 device 002 >>> fan1: 30 RPM (div = 4) >>> fan2: 0 RPM >>> fan3: 30 RPM >>> fan4: 30 RPM >> >> >> sensors max6651-i2c-1-48 >> max6651-i2c-1-48 >> Adapter: DaVinci I2C adapter >> fan1: 30 RPM (div = 4) >> fan2: 30 RPM >> fan3: 420 RPM >> fan4: 30 RPM >> >>> Only fan2 (TACH1 chip input) has the resistor installed. >> >> >> We have it both on fan1 and fan4. >> >> If I use our scope for checking the tachometer, I see level zero on >> the scope, but 1 when checking the open collector level, since that is >> the purpose of the pull-up resistor. >> > With the pull-up installed, you should always see a high voltage on the > scope or with a volt meter. The scope would not see or be able to know > that the pin is OC if the pull-up resistor is there. > > If it is truly OC, it would be floating and might show low. If you can, > I would suggest to manually add a 10k resistor against VCC to the open > connector and see what happens. > > Another way to find out for sure might be to disconnect power and > measure resistance between the tachometer pin and VCC. Perhaps I was not clear. So, we do have both the resistors and capacitor as required. I double checked the schematics as well as the pins coming from the fan and that was zero. The tacho0 input, however, was 1. -- 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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