Prof. Dr. Peter A. Henning wrote:
> Hi there,
>
> Am Freitag, 7. Januar 2005 21:14 schrieb Aurelien Jarno:
>
>>>111111111111111111111111111111111111111111111111111111111
>>>Detection of the DS1621 in sensors-detect is broken. According to the
>>>data sheet of the DS1621, one bit of the configuration register is always
>>>1 and another always 0. This is simply not true, if the chip is not
>>>properly initialized. I suggest the following replacement for sub
>>>ds1621_detect in sensors-detect
>>
>>That sounds me strange. I am using a ds1621 plugged onto my parallel
>>port I2C interface and the module is always loaded at boot. I am using
>>this for more than 4 years (the chip is dated 0022, ie year 2000 week
>>22).
>
>
> Well, may be strange - but that's fact. The data sheet does not have a single
> line indicating that the two "fixed" bits may be overwritten - and yet,
> something does this.
Ok, I have done some tests on my ds1621 chip, and I can't write to bits
3 and 2, there are always respectively 1 and 0.
However, I have seen that Dallas has released a new datasheet for the
DS1621 which now presents the two bits as 'X', and marks them as
'reserved'. I suspect they have done some changes in there design,
that's why you are having some problems.
I have looked to the datasheet to find a way to detect the DS1621 chip.
Here is my proposal:
1) Verify that the 7 lowest bits of the TL register are 0. This is
basically what you proposed. It is specified in the datasheet that's
these bit are always 0, and I doubt it will change in the future
(because in that case a lot of existing design won't work anymore).
2) Verify that bit 4 of the config register is 0. It means that the chip
is not currently writing to its EEPROM, or that no EEPROM write has been
requested in the last 10ms. I think we could safely say that it is
always the case with the kernel driver.
3) Issue a "stop conversion T" (= sending 0x22 to the chip), and verify
that the bit 7 of the config register is set to 1 (no conversion in
progress).
Any comment on using such a detection? If everybody agrees, I'll send a
patch for both the 2.4 and 2.6 modules.
Bye,
Aurelien
--
.''`. Aurelien Jarno GPG: 1024D/F1BCDB73
: :' : Debian GNU/Linux developer | Electrical Engineer
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