Hi all, I am using the PyUSB 1.0 module with libusb 1.0 for a backend, Python 2.7, on an embedded Linux system running Debian 7.0 (Wheezy). To describe my issue, I think that I must provide a little background about my project. I am using PyUSB to facilitate USB control of a spectrum analyzer (i.e., a Spectran HF-60105 V4 X) using the device's API. The embedded computer and spectrum analyzer are a part of a field deployable system, and as such, the system must be able to operate at temperatures below freezing (but of course, above the documented temperature specifications for all hardware). This is where I run into problems. Specifically, my code works without a hitch when it is warm outside, but it seems to run into an issue when it's operating in cooler temperatures (i.e., around freezing). Below is a snippet of command line output from the Python script when it is warm outside (i.e., room temperature), and all is working fine. The hex that follows each API command is the device's response. The "verify" response is unique, but the response to all other commands is a generic "/x31/x60/x21/x00", which confirms reception by the device.
Verify.....................SUCCESSFUL. /x31/x60/x01/x51/x1a/xf5/xaf Initial boot calib.........SUCCESSFUL. /x31/x60/x21/x00 Preamplifier...............ON. /x31/x60/x21/x00 Attenuation................OFF. /x31/x60/x21/x00 Start frequency........... 99.5 MHz. /x31/x60/x21/x00 Stop frequency............ 101.5 MHz. /x31/x60/x21/x00 RBW....................... 1000 Hz. /x31/x60/x21/x00 Sweep delay accuracy.......ON. /x31/x60/x21/x00 Sweep reset................SUCCESSFUL. /x31/x60/x21/x00 However, when the system is operating in cooler temperatures, near freezing, the device's responses appear to be delayed. Basically, it appears that the device.read() commands are timing out without a response at first, but the device's responses seem to be queued up in a buffer, because eventually multiple "OK" responses are received by the computer. In the example shown below, all ends up just fine, because the commands eventually are received by the analyzer. However, this doesn't always happen, so this glitch is currently a showstopper for my system. Here's output from the system when it's around freezing: Verify.....................FAILED. /x31/x60 Verify.....................SUCCESSFUL. /x31/x60/x01/x51/x1a/xf5/xaf/x01/x51/x1a/xf5/xaf Initial boot calib.........FAILED. /x31/x60 Initial boot calib.........FAILED. /x31/x60 Initial boot calib.........FAILED. /x31/x60 Initial boot calib.........SUCCESSFUL. /x31/x60/x21/x00/x21/x00/x21/x00/x21/x00 Preamplifier set...........FAILED. /x31/x60 Preamplifier set...........FAILED. /x31/x60 Preamplifier set...........FAILED. /x31/x60 Preamplifier...............ON. /x31/x60/x21/x00/x21/x00/x21/x00/x21/x00 Attenuator set.............FAILED. /x31/x60 Attenuator set.............FAILED. /x31/x60 Attenuator set.............FAILED. /x31/x60 Attenuation................OFF. /x31/x60/x21/x00/x21/x00/x21/x00/x21/x00 Start frequency set.......FAILED. /x31/x60 Start frequency set.......FAILED. /x31/x60 Start frequency set.......FAILED. /x31/x60 Start frequency........... 99.5 MHz. /x31/x60/x21/x00/x21/x00/x21/x00/x21/x00 Stop frequency set........FAILED. /x31/x60 Stop frequency set........FAILED. /x31/x60 Stop frequency............ 101.5 MHz. /x31/x60/x21/x00/x21/x00/x21/x00 RBW set...................FAILED. /x31/x60 RBW set...................FAILED. /x31/x60 RBW set...................FAILED. /x31/x60 RBW....................... 1000 Hz. /x31/x60/x21/x00/x21/x00/x21/x00/x21/x00 Sweep delay accuracy.......FAILED. /x31/x60 Sweep delay accuracy.......FAILED. /x31/x60 Sweep delay accuracy.......FAILED. /x31/x60 Sweep delay accuracy.......ON. /x31/x60/x21/x00/x21/x00/x21/x00/x21/x00 Sweep reset................FAILED. /x31/x60 Sweep reset................FAILED. /x31/x60 Sweep reset................FAILED. /x31/x60 Sweep reset................SUCCESSFUL. /x31/x60/x21/x00/x21/x00/x21/x00/x21/x00 I'm at a complete loss as to why I'm observing this trend, which is very repeatable. I've isolated the embedded board and tested its functionality in the cold; it's just fine. I've communicated with the manufacturers of the spectrum analyzer, and they do not report any issues with the device at these "near freezing" temperatures, being well above the analyzer's lowest operational temperature of -20 C. Furthermore, when I use the manufacturer's proprietary software to interface with the analyzer, it behaves just fine even at the cooler temperatures in question. Tying this back into PyUSB, I'm curious if anyone out there has dealt with something like this and might have recommendations for USB communication parameters to adjust or specific PyUSB functions or objects that might help me diagnose my issue. Thanks in advance for your time! Best, Sam
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