Les Smithson's Python extension for LegOS LNP

Introduction

Please note that this does not allow you to run Python on the RCX.

If you don't know what Python is, look here. It should be ready-installed on most standard Linux distributions.

Here's a quick example Python script that sends a message to the brick, and prints a reply:

 
# Import the LNP extension. This initializes lnp
import lnp
# Send a message to the RCX
lnp.iwrite('hello')
# Read & print the response
lnp.iread()
'world'
 

Simple, Eh?

Pylnp supports integrity & addressing read/write operations. Read calls may be blocking or non-blocking (although non-blocking reads don't work yet.)

Download

Installation & Running

• Download the pylnp.tar file.
• Type tar -xf pylnp.tar to untar the file. This should create the directory pylnp, containing the files Setup, lnpext.c and lnpmodule.so.
• Start the lnpd daemon. You should also ensure that the lnp shared libraries are in your $LD_LIBRARY_PATH.
• cd into the pylnp directory.
• Type python, followed by import lnp and your ready! As soon as you do the import, the IR tower light should come on. If you get the message IOError: Failed to talk to IR tower, either python hasn't found the lnp extension, or lnpd isn't working. Check your setup & try again.
• The Setup and lnpext.c files are provided if you want to play with the pylnp source. To rebuild, follow the standard python extension instructions.

Documentation

lnp.__doc__

 
This module interfaces to LegOS lnp, using the lnpd package from 
Martin Cornelius (Martin.Cornelius@t-online.de). It allows a python script 
to send & received data via the IR tower to an RCX running LegOS. The
following functions are available:
  iread()                Blocking LNP integrity read
  ireada(callable)       Asynchronous LNP integrity read
  iwrite(buf)            LNP integrity write
  aread(port)            Blocking LNP addressing read
  areada(port, callable) Asynchronous LNP addressing read
  awrite(buf, dst, src)  LNP addressing write 

All reads are mutually exclusive. That is, only one asynchronous or
blocking integrity or addressing read may be outstanding at one time.
 

lnp.aread.__doc__

 
aread(port)

Performs a blocking LNP addressing read on port 'port', returning
the result as the tuple (buf, port), where buf is the buffer string
read from the RCX and 'port' is the RCX source port number. The
string may contain embedded nulls. Any outstanding asynchronous LNP
reads (integrity or addressing) are cancelled.
 

lnp.areada.__doc__

 
aread(port)

Performs a blocking LNP addressing read on port 'port', returning
the result as the tuple (buf, port), where buf is the buffer string
read from the RCX and 'port' is the RCX source port number. The
string may contain embedded nulls. Any outstanding asynchronous LNP
reads (integrity or addressing) are cancelled.
>>> print lnp.areada.__doc__
areada(port, callable)

Performs an asynchronous LNP addressing read. The callable object
'callable' is called with the string read from the RCX, and the RCX
port number. The string may contain embedded nulls. Any outstanding
asynchronous LNP integrity reads are cancelled.
 

lnp.awrite.__doc__

 
awrite(buf, dst, src)

Performs LNP addressing write, sending the buffer buf to the RCX.
The string may contain embedded nulls. dst & src are the lnp
destination & source ports.
 

lnp.iread.__doc__

 
iread()

Performs a blocking LNP integrity read, returning the result as a
string. The string  may contain embedded nulls. Any outstanding
asynchronous LNP reads (integrity or addressing) are cancelled.

lnp.ireada.__doc__

 
ireada(callable)

Performs an asynchronous LNP integrity read. The callable object 'callable' 
is called with the string read from the RCX. The string may contain 
embedded nulls. Any outstanding asynchronous LNP addressing reads are
cancelled.
 

lnp.iwrite.__doc__

 
iwrite(buf)

Performs LNP integrity write, sending the buffer buf to the RCX.
The string may contain embedded nulls.

Application Notes

Pylnp allows you to embed nulls in the data, so you can send binary as well as ordinary strings. Use the python struct module to handle binaries.

Multi-threaded applications must ensure that any lnp.read calls are made in the main thread. This is because python only delivers signals to the main thread.

It ought to be possible for a LegOS RCX program to send some python script to pylnp for interpretation. This might be usefull for pretty-printing data structures etc.

I've used pylnp as part of a gdb/legOS interface (see here for more info.). It sends messages between gdb connected via a socket & a debug stub running under legOS.

Disclaimer

Consulting

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