> 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@desktop:~$ 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.
I am currently clueless. Fwiw, I am now using linux kernel 3.2.1 for
the moment. I cannot see any bugfixes in the log with regards to that,
though. I am still not sure what is going on, so I cannot claim that
it is a bug, nor can I exclude it. Any help would be appreciated.
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