#
# Interface for VISA devices through tty
# 
#
import os, threading, termios

class VISA:
    def __init__(self, tty_name, out_sink, readLen=100):
        self.tty = os.open(tty_name, os.O_RDWR)
        self.addr = None
        self.out = out_sink  # Function that takes a string
        self.read_len = readLen
        self.startThread()
        self.setAddress(0)

    def startThread(self): # To run read in parallel with write
        self.thread = threading.Thread(target=self.read)
        self.thread.daemon = True
        self.thread.start()

    def read(self):
        while (True):
            self.out( os.read(self.tty, self.read_len) )    

    def cmd(self, cmd_str):
        os.write(self.tty, cmd_str + "\n")
	# I tried to fix this with the following call, but it did not change anything
        # termios.tcflush(self.tty, termios.TCIOFLUSH)

    def setAddress(self, a):
        if self.addr == a:
            return False
        self.cmd("++addr %s" % a)
        self.addr = a
        return True

    def getVersion(self):
        return self.cmd("++ver")

############# You can ignore the next two classes ##########
####### The part that executes is below them ########

class Device:
    def __init__(self, controller, address):
        self.cont = controller
        self.addr = address

    def cmd(self, cmd_str):
        self.cont.setAddress(self.addr)
        self.cont.cmd(cmd_str)

    

class PowerSupply(Device):
    def reset(self):
        self.cmd("RST?")

########### Executing part ###########

def printOut(out):
    print(out)


v = VISA("/dev/ttyUSB0", printOut)
v.cmd("++addr")
v.cmd("++ver")