RCX using python serial help

[Astan Chee]

Hi,
I've got a lego mindstorm RCX 1.0 (but firmware is 2.0) that uses one of
those old serial IR towers to control the microcontroller. I've had a look
around at python's serial documentation as well as the RCX's documentation
and I'm trying to write something to control the RCX directly using python.
Several examples from of doing this in python include using lnp (i think)
and that doesn't quite run well in windows. I've had a look at the C++ code
and some protocol documentation here:
http://www.generation5.org/content/2001/rob08.asp and converted it to
python. I've attached it at the end of the email. So now I've figured out
how to check for the battery level and it seems to work (I've tested it on
my RCX) but I'm confused with the other documentation (e.g.
http://graphics.stanford.edu/~kekoa/rcx/ ) about how to do this in python or
what this all means. I was wondering if anyone can help me complete these?
or maybe help me do it step-by-step?
Thanks for any help.

Below is the python code I've been working on:

import time
import serial
import struct
import binascii

def tcbin(x, y=8):
    """
    This function returns the padded, two's complement representation of x,
in y-bits.
    It is conventional for y to be 8, 16, 32 or 64, though y can have any
non-zero positive value.
    """
    if x >= 0:
        binstr = bin(x)
        # pad with leading zeros
        while len(binstr) < y + 2:
            binstr = "0b0" + binstr[2:]
        return binstr
    return bin((2**y) + x) # x is negative

def bitcompliment(hex_code):
    return hex(int(tcbin(~(ord(hex_code))),2))

def processOutput(raw_data,output):
    outputStatus = True
    pos = 0
    for i in range(3):
        if raw_data[i] != output[i]:
            outputStatus = False
        pos+=1
    if outputStatus:
        print "output OK"
    else:
        print "problem with output"
    outputCompliment = True
    while outputCompliment:
        if hex(ord(output[pos])) == bitcompliment(output[pos+1]):
            print "output compliment OK"
        else:
            print "problem with output compliment"
        pos+=2
        if hex(ord(output[pos])) == '0x55' and hex(ord(output[pos+1])) ==
'0xff' and hex(ord(output[pos+2])) == '0x0':
            pos+=3
            outputCompliment = False
    if hex(ord(output[pos])) == '0xcf' or hex(ord(output[pos])) == '0xc7':
        #battery checker
        pos+=2
        if hex(ord(output[pos])) == bitcompliment(output[pos+1]) and
hex(ord(output[pos+2])) == bitcompliment(output[pos+3]):
            s = ((ord(output[pos+2]) * 256) + ord(output[pos])) / 1000.0
            print "Battery is at " + str(s) + " Volts"
    else:
        for i in range(len(output[pos:]),len(output),2):
            print hex(ord(output[i]))
            if i+1 < len(output):
                if hex(ord(output[i])) == bitcompliment(output[i+1]):
                    print "message OK. contents: " +
hex(ord(output[i]))

# configure the serial connections (the parameters differs on the device you
are connecting to)
ser = serial.Serial(
 port='COM1',
 baudrate=2400,
 parity=serial.PARITY_ODD,
 stopbits=serial.STOPBITS_ONE,
 bytesize=serial.EIGHTBITS
)
raw_data = '\x55\xff\x00\x38\xc7\x38\xc7'
result = ser.write(raw_data)
out = ''
time.sleep(1) #pause for a second
while ser.inWaiting() > 0:
    out+=ser.read(1)
processOutput(raw_data,out)
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