Jean,
this is my i2cdump output:
[root at CANTastic:/qs]# ./i2cdump 1 0x48
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/1, address 0x48, mode byte
Continue? [Y/n]
0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
00: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
10: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
20: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
30: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
40: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
50: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
60: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
70: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
80: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
90: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
a0: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
b0: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
c0: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
d0: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
e0: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
f0: 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 1f 00 c9 c9 ?.???.???.???.??
and in word dump mode:
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c/1, address 0x48, mode word
Continue? [Y/n]
0,8 1,9 2,a 3,b 4,c 5,d 6,e 7,f
00: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
08: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
10: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
18: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
20: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
28: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
30: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
38: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
40: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
48: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
50: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
58: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
60: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
68: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
70: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
78: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
80: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
88: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
90: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
98: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
a0: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
a8: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
b0: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
b8: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
c0: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
c8: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
d0: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
d8: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
e0: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
e8: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
f0: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
f8: 501f 0000 00c9 00c9 501f 0000 00c9 00c9
I will investigate more time next week.
Have a nice weekend.
Ralf
>
> > I have done this, and i have read back the shadowed register values.
> >
> > The max6626 data sheet says:
> > Pointer Register - D7 to D2: Will read all zeros, cannot be written.
> >
> > Because the D2..D7 cannot be written, the leaving pinter register bits
> > are 0..1
> > which shows the register shadow effect.
>
> Please understand that there are two different phenomenons on the LM75:
> 1* Registers cycle over 8-addr boudaries.
> 2* addresses 0x04-0x07 are not mapped to any register.
>
> If I read you correctly, the MAX6626 is somewhat different in that it
> cycles over 4-addr boudaries. This would be enough to reliably
> differenciate between both chips.
>
> Note that this is really a detection/identification trick. Both chips
> only really have 4 registers at addresses 0x00-0x03.
>
> I would really like to see the output of i2cdump. Care to post it here?
>
> > O.k. I aggree, but the problem I currently see is,
> > that I have to distinguish between the LM75 and MAX6626 to select
> > the appropriate conversion and detection functions.
> > Because both chips use the same addresses I think it is not possible
> > to do this in automated way. What do you think?
>
> According to what I said above it doesn't sound impossible (unless I
> missed your point).
>
> That said I see no reason to differenciate. On the LM75 the extra bits
> (10-12) will always read 0 which is compatible with the MAX6626.
> Considering that every (LM75-compatible) chip has 12-bit resolution
> shouldn't hurt. Note that in 2.6 all temperatures are reported to
> user-space in millidegree C anyway.
>
> If you are able to differenciate between both chips, then you can
> introduce a new kind for the max6626 and handle the 3 extra resolution
> bit for it only. However, a new kind means that you have to add support
> to libsensors, sensors, and virtually any application relying on
> libsensors. I seriously doubt it's worth the pain, which is why I'd
> stick to the lm75 name for everyone and extend the reolution to 12 bits
> for everyone as well.
>
> Thanks,
>
> --
> Jean Delvare
> http://khali.linux-fr.org/
>
>
