From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Cole <clecol-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: i2cset question
Date: Fri, 17 Apr 2009 10:33:38 -0400
Message-ID: <49E89342.1010807@gmail.com>
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To: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: linux-i2c@vger.kernel.org

Hey all, I found the i2c-tools and lm-sensors packages today...great 
stuff! I had a question about using i2cset properly. I'm trying to set 
the value of a digital potentiometer (maxim 5434L) over the i2cbus, and 
I can tell by using i2cdump that it's setting the register value 
properly...but I keep getting "Warning - readback failed" after i use 
i2cset. Here's the output of what I'm trying to do:

ccole@test:~$ sudo modprobe scx200_acb
ccole@test:~$ sudo modprobe i2c-dev
ccole@test:~$ sudo su -
root@test:~# i2cdetect -l
i2c-0    smbus         CS5536 ACB0                         SMBus adapter

root@test:~# i2cdetect 0
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-0.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
root@test:~# i2cdump 0 0x50
No size specified (using byte-data access)
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-0, address 0x50, mode byte
Continue? [Y/n] y
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 80 08 07 0d 0b 01 40 00 04 60 70 00 82 08 00 01    ??????@.?`p.??.?
10: 0e 04 0c 01 02 20 c0 75 70 00 00 48 30 48 2a 80    ????? ?up..H0H*?
20: 80 80 45 45 00 00 00 00 00 3c 48 30 2d 55 00 01    ??EE.....<H0-U.?
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 68    ..............?h
40: 7f 7f 7f 7f 7f ba 00 00 00 56 4c 34 37 30 4c 36    ??????...VL470L6
50: 7f 32 33 2d 42 33 53 00 00 00 00 00 00 00 00 00    ?23-B3S.........
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
90: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
b0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
c0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................

root@test:~# i2cset 0 0x50 0x50 0x21
No size specified (using byte-data access)
WARNING! This program can confuse your I2C bus, cause data loss and worse!
DANGEROUS! Writing to a serial EEPROM on a memory DIMM
may render your memory USELESS and make your system UNBOOTABLE!
I will write to device file /dev/i2c-0, chip address 0x50, data address
0x50, data 0x21, mode byte.
Continue? [y/N] y
Warning - readback failed

root@test:~# i2cdump 0 0x50
No size specified (using byte-data access)
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-0, address 0x50, mode byte
Continue? [Y/n] y
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 80 08 07 0d 0b 01 40 00 04 60 70 00 82 08 00 01    ??????@.?`p.??.?
10: 0e 04 0c 01 02 20 c0 75 70 00 00 48 30 48 2a 80    ????? ?up..H0H*?
20: 80 80 45 45 00 00 00 00 00 3c 48 30 2d 55 00 01    ??EE.....<H0-U.?
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 68    ..............?h
40: 7f 7f 7f 7f 7f ba 00 00 00 56 4c 34 37 30 4c 36    ??????...VL470L6
50: 21 32 33 2d 42 33 53 00 00 00 00 00 00 00 00 00    !23-B3S.........
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
90: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
b0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
c0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................

root@test:~# i2cset 0 0x50 0x50 0x00
No size specified (using byte-data access)
WARNING! This program can confuse your I2C bus, cause data loss and worse!
DANGEROUS! Writing to a serial EEPROM on a memory DIMM
may render your memory USELESS and make your system UNBOOTABLE!
I will write to device file /dev/i2c-0, chip address 0x50, data address
0x50, data 0x00, mode byte.
Continue? [y/N] y
Warning - readback failed

root@test:~# i2cdump 0 0x50
No size specified (using byte-data access)
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-0, address 0x50, mode byte
Continue? [Y/n] y
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 80 08 07 0d 0b 01 40 00 04 60 70 00 82 08 00 01    ??????@.?`p.??.?
10: 0e 04 0c 01 02 20 c0 75 70 00 00 48 30 48 2a 80    ????? ?up..H0H*?
20: 80 80 45 45 00 00 00 00 00 3c 48 30 2d 55 00 01    ??EE.....<H0-U.?
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 68    ..............?h
40: 7f 7f 7f 7f 7f ba 00 00 00 56 4c 34 37 30 4c 36    ??????...VL470L6
50: 00 32 33 2d 42 33 53 00 00 00 00 00 00 00 00 00    .23-B3S.........
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
90: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
b0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
c0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................


Thanks,
  Chris