Unfortunately my every day job has gotten most of my time lately and I haven’t been able to make much progress on anything. But today I had some time to play around with my new cubieboard based Fileserver and the old Microsoft Kinect I had laying around for a while now (I’ll write about that in the next post). And while I was playing around I got reminded of a very powerful Python library called numpy, which helped me solve a minor problem I still had with my TEMPer USB driver. Previously I had a problem with reading temperatures below zero, as the TEMPer protocol uses a signed integer as a datatype for the temperature and Python doesn’t have a native one Byte signed integer. But luckily numpy remedies the problem with its own datatypes, among them a one Byte signed integer (int8). So I shortly turned away from my Kinect/cubieboard endavour to fix the TEMPer driver. The solution is simple, I add numpy to my imports and convert the retrieved temperature value to numpys int8, so the final code looks like this:

import sys, os, time, usb, numpy
 
VENDOR_ID = 0x0c45
PRODUCT_ID = 0x7401
 
INTERFACE1 = 0x00
INTERFACE2 = 0x01
 
reqIntLen=8
reqBulkLen=8
endpoint_Int_in=0x82 #/* endpoint 0x81 address for IN */
endpoint_Int_out=0x00 #/* endpoint 1 address for OUT */
 
uTemperatura = [ 0x01, 0x80, 0x33, 0x01, 0x00, 0x00, 0x00, 0x00 ]
uIni1 = [ 0x01, 0x82, 0x77, 0x01, 0x00, 0x00, 0x00, 0x00 ]
uIni2 = [ 0x01, 0x86, 0xff, 0x01, 0x00, 0x00, 0x00, 0x00 ]

calibration = 0

def setup_libusb_access():
        for bus in usb.busses():
                for dev in bus.devices:
                        if dev.idVendor == VENDOR_ID and dev.idProduct == PRODUCT_ID:
                                print "Found Temper"
                                return dev
                        else:
                                print "searching for Temper Devices..."
        print "no devices found"
        return None

def ini_control_transfer(connection):
        question = [0x01, 0x01]
        
        # Detaching Kernel drivers on interfaces if any are present
        try:
                connection.detachKernelDriver(INTERFACE1)
        except:
                print "couldn't detach Kernel driver for interface1"
        try: 
                connection.detachKernelDriver(INTERFACE2)
        except:
                print "couldn't detach Kernel driver for interface2"
        
        # claim interfaces
        try:
                connection.claimInterface(INTERFACE1)
                connection.claimInterface(INTERFACE2)
        except:
                print "couldn't claim one of the interfaces"
        
        r = connection.controlMsg(requestType=0x21, request=0x09, value=0x0201, index=INTERFACE1, buffer=question)
        if r < 0:
                print "Control Message failed"
                return False
        return True
        
def control_transfer(connection, question):
        r = connection.controlMsg(requestType=0x21, request=0x09, value=0x0200, index=INTERFACE2, buffer=question)
        return 
        
def interrupt_read(connection):
        r = connection.interruptRead(endpoint_Int_in, reqIntLen)
        return
        
def interrupt_read_temperature(connection):
        answer = connection.interruptRead(endpoint_Int_in, reqIntLen)
        
        #debug output
        print "read_temperature answer:"
        print answer
        
        tmp = numpy.int8(answer[2])
        
        temperature = (answer[3] & 0xFF) + (tmp << 8)
        temperature += calibration
        tempC = temperature * (125.0 / 32000.0)

        return tempC
        
        
def usb_release_interface(con, iface):
        try:
                con.releaseInterface()
        except:
                pass
        
def usb_close(con):
        con.reset()

def main(argv):
        temper = setup_libusb_access()
        
        if (temper == None):
                sys.exit(17)
        connection = temper.open()
        connection.reset()
        
        ini_control_transfer(connection)
        
        control_transfer(connection, uTemperatura )
        interrupt_read(connection)
        
        control_transfer(connection, uIni1 )
        interrupt_read(connection)
        
        control_transfer(connection, uIni2 )
        interrupt_read(connection)
        interrupt_read(connection)
        
        while 1:
                try:
                        control_transfer(connection, uTemperatura )
                        tempc = interrupt_read_temperature(connection)
                        
                        print time.time()
                        print str(tempc)+" C"
                        
                        time.sleep(1)
                except KeyboardInterrupt:
                        print "Execution Interrupted by User"
                        break
                        
        usb_release_interface(connection, INTERFACE1)
        usb_release_interface(connection, INTERFACE2)
        
        usb_close(connection)
        
        return 0

if __name__ == "__main__":
        main(sys.argv)

Notice the line that says:

tmp = numpy.int8(answer[2])

That’s all I needed to fix the temperature readout for negative values.
Now on to writing the next post…