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Date: Mon, 10 Mar 2014 18:00:17 +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 3:11 PM, Guenter Roeck <linux@...ck-us.net> wrote: > On Mon, Mar 10, 2014 at 01:50:01PM +0000, Laszlo Papp wrote: >> 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. >> > > How can the pin coming from the fan be zero, and the tach0 input be 1 > at the same time ? Those should be the same ? Nope, that is what the pull-up resistor is for. It will pull the level up to 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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