Public bug reported:
The version of digitemp_DS2490 in Trusty and later (and possibly
previous versions, though it has worked for us before) does not detect
temperature sensors connected to the One-wire network. For reference,
we're using
digitemp:i386/trusty 3.6.0+dfsg1-2
but it is likely that other versions are affected too.
To reproduce:
- Connect some temperature sensors via a DS2490 USB-to-1wire adapter
- Run: digitemp_DS2490 -i
Expected results:
- The sensors are detected and listed on the output (and in a .digitemprc
file); this takes a few seconds
Actual results:
- No sensors are detected; the program returns immediately.
Diagnosis:
This seems to be a (long-standing?) bug in how the code resets the 1-Wire bus
via USB. There are a number of issues:
- The DS2490 returns the operation result via interrupt data, but the program
reads it via normal data.
- A result is only returned if the appropriate bit is set to request it; the
program does not set this bit.
- The program requests 32 (0x20) bytes from the USB device, but does not check
how many were actually returned (and hence whether any result actually came
back) - the device will always return 16 (0x10) status bytes, but any result
bytes follow these.
Thus the program detects status or failure by reading a byte in the
buffer that the device has not actually modified. In cases where the
program worked, this is likely to be because the value happened to be
set to the right value (0 will do) by chance.
Fix:
I'll attach a patch to the bug that addresses these issues.
** Affects: digitemp (Ubuntu)
Importance: Undecided
Status: New
** Patch added: "Patch to fix issue reading result after resetting 1wire bus
via USB"
https://bugs.launchpad.net/bugs/1397382/+attachment/4270220/+files/usb-reset-status.patch
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https://bugs.launchpad.net/bugs/1397382
Title:
digitemp_DS2490 fails to detect sensors
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