Multimeter USB output

[Joe]

Am 28.08.2016 um 00:45 schrieb 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.
 >

Yes, I saw this:

Starting
Multimeter was found

The UT61B has two interfaces, a RS232C interface and this usb interface. 
The RS232 interface works well with PySerial. It continously transmits 2 
.. 3 Pakets per second with 14 Bytes each. This happens unsolicited 
without any command as long as the RS232C/USB button on the DMM is active.

So I assumed the USB interface also doesn't need any command and also
transmit this stream of 2 to 3 Pakets per second. But unfortunately I 
don't have any doc for the USB interface for this device.

To the accompanying software of the UT61B there is a ready windos app 
which shows and logs the output of the UT61B. This app can be switched 
between RS232C and USB; both work.

I asked the manufacturer (Uni-T in Shenzen) for additional info and are 
now waiting for an answer.

Assumed the USB interface sends this 2 to 3 pakets per second 
unsolicited - should the code shown work? Is this ok:


 >>              lambda e: \
 >>                 usb.util.endpoint_direction(e.bEndpointAddress) == \
 >>                 usb.util.ENDPOINT_IN)

I am in doubt: Is usb.util.ENDPOINT_IN really correct?

Thanx - Joe