usbdiscover.py

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import serial, os, time, atexit

lockfilepath = None
portnum = 0


def removelockfiles():
        os.system("rm -f /tmp/dev_ttyUSB*")
        
def removelockfile():
        if os.path.exists(lockfilepath):
                os.remove(lockfilepath)

atexit.register(removelockfile)


def checkBoardId(idstring, ser):
        ser.reset_input_buffer()
        ser.write("x\n") # check board id
        line = ""
        time.sleep(0.1)
        while ser.inWaiting() > 0:
                line = ser.readline().strip()

        if not line == idstring:
                print("incorrect board id: "+line)
                return False
        
        print("connected to: "+line)
        return True
        
        
def usbdiscover(idstring, TIMEOUT):
        global lockfilepath, portnum

        while portnum <= 6:
                port = '/dev/ttyUSB'+str(portnum)

                print("trying port: "+port)
                
                lockfilepath = "/tmp/dev_ttyUSB"+str(portnum)
                tries = 0
                while tries < 5:
                        if os.path.exists(lockfilepath):
                                print("port busy: "+port)
                                time.sleep(1)
                                tries += 1
                        else:
                                break 

                if tries == 5:
                        print("giving up on port: "+port)
                        portnum += 1
                        continue
                        
                open(lockfilepath, 'w') # creates lockfile
                
                try:
                        ser = serial.Serial(port, 115200, timeout=TIMEOUT)
                except serial.SerialException: 
                        print("port exception: "+port)
                        os.remove(lockfilepath)
                        portnum += 1
                        time.sleep(1)
                        continue
                        
                time.sleep(2)

                if checkBoardId(idstring, ser):
                        break
                        
                ser.close()
                if os.path.exists(lockfilepath):
                        os.remove(lockfilepath)
                time.sleep(1)
                portnum += 1
                
        if not ser.is_open:
                print("device not found")
                sys.exit(0)
        
        return ser