diff options
| author | David Fries <david@fries.net> | 2008-01-22 03:31:39 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-01-22 09:17:48 -0800 |
| commit | 80c002ddd2e732062e4371314d40515d0b5d8415 (patch) | |
| tree | 77ca216b3b655c1362c4bfaa130fea67f529d770 /drivers | |
| parent | 941ed3b53086697eac7449f3ab5d2c5ab3259de2 (diff) | |
W1: w1_therm.c is flagging 0C etc as invalid
The extra rom[0] check is flagging valid temperatures as invalid when
there is already a CRC data transmission check.
w1_therm_read_bin()
if (rom[8] == crc && rom[0])
verdict = 1;
Requiring rom[0] to be non-zero will flag as invalid temperature
conversions when the low byte is zero, specifically the temperatures 0C,
16C, 32C, 48C, -16C, -32C, and -48C.
The CRC check is produced on the device for the previous 8 bytes and is
required to ensure the data integrity in transmission. I don't see why the
extra check for rom[0] being non-zero is in there. Evgeniy Polyakov didn't
know either. Just for a check I unplugged the sensor, executed a
temperature conversion, and read the results. The read was all ff's, which
also failed the CRC, so it doesn't need to protect against a disconnected
sensor.
I have more extensive patches in the work, but these two trivial ones will
do for today. I would like to hear from people who use the ds2490 USB to
one wire dongle. 1 if you would be willing to test the patches as I
currently only have the one sensor on a short parisite powered wire, 2 if
there is any cheap sources for the ds2490.
Signed-off-by: David Fries <david@fries.net>
Acked-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/w1/slaves/w1_therm.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c index feed89e733e..112f4ec5903 100644 --- a/drivers/w1/slaves/w1_therm.c +++ b/drivers/w1/slaves/w1_therm.c @@ -204,7 +204,7 @@ static ssize_t w1_therm_read_bin(struct kobject *kobj, crc = w1_calc_crc8(rom, 8); - if (rom[8] == crc && rom[0]) + if (rom[8] == crc) verdict = 1; } } |