Multimeter USB output

[Terry Reedy]

On 8/27/2016 3:35 PM, Joe wrote:
> Hi,
>
> I'm using Python 3.5.1 with PyUSB 1.0 under Win 10 (64). We try to read
> the USB output of a DMM 'UT61B'.
>
> import usb.core
> import usb.util
> import usb.backend.libusb1
>
> def Gosub():
>      dev = usb.core.find(idVendor=0x1a86, idProduct=0xe008) # Digital
> Multimeter UT61B
>      if dev == None:
>          print ('Multimeter not found')
>      else:
>          print ('Multimeter was found')
>          dev.set_configuration()
>          cfg = dev.get_active_configuration()
>          intf = cfg[(0,0)]
>          ep = usb.util.find_descriptor(
>              intf,
>              custom_match = \
>              lambda e: \
>                 usb.util.endpoint_direction(e.bEndpointAddress) == \
>                 usb.util.ENDPOINT_IN)
>          if ep == None:
>              print ('ep is None')
>          else:
>              s = ep.read(64, 500)
>              print ('Len s: ' + len(s))
>
> print ('Starting')
> Gosub()
> print ('Ready.-')
>
> Result:

I presume you saw
Starting
Multimeter was found

> File "d:\work-d\PythonProgs\ut61b.py", line 27, in <module>
>    Gosub()
> File "d:\work-d\PythonProgs\ut61b.py", line 23, in Gosub
>    s = ep.read(64, 500)
> File "D:\Python3\Lib\site-packages\usb\core.py", line 402, in read
>    return self.device.read(self, size_or_buffer, timeout)
> File "D:\Python3\Lib\site-packages\usb\core.py", line 988, in read
>    self.__get_timeout(timeout))
> File "D:\Python3\Lib\site-packages\usb\backend\libusb1.py", line 851, in
> intr_read
>    timeout)
> File "D:\Python3\Lib\site-packages\usb\backend\libusb1.py", line 936, in
> __read
>    _check(retval)
> File "D:\Python3\Lib\site-packages\usb\backend\libusb1.py", line 595, in
> _check
>    raise USBError(_strerror(ret), ret, _libusb_errno[ret])
>
> usb.core.USBError: [Errno 10060] Operation timed out
>
> What's wrong? How to fix?

Read (again?) the doc for the interface for the device.  Because reading 
timed out, I suspect that it is waiting for a command for it to send 
something.

-- 
Terry Jan Reedy