Copyright © 1998, 2001 by Ian Horswill, see comment within this file.

Porting the GRL compiler to your environment

To make GRL work on your robot you need to:

1. Choose a target language.  If you can run Scheme48 directly on your robot, then you can compile GRL directly into your scheme interpreter and program interactively.  Otherwise, you need to cross-compile.  If cross-compiling, C++ is the preferred backend, since it has some extra features and is the only one that has users at the moment.  However, the other backends are still serviceable and we still support them.
2. Port the run-time system.  There are a small number of procedures and global variables that GRL needs to be there to run properly.  Specifically, the clock-related variables (%ms-clock, %clock-period, %measured-clock-period) and the update_grl_time() procedure that sets them.  You also need to make sure exit() exists if you're going to use it from GRL.  If you are not running in one of our supported environments, you will need to modify our boilerplate versions to fit your OS.
3. Write wrappers for your sensors and effector drivers.  Basically, you need to
   • Define the format of the motor-vector for your base
   • Implement a transducer that takes one of these motor vectors as an argument and calls the appropriate low-level routines in your target language to set the motor velocities.  That is, write something like:
     
     (define-transducer (drive-base-internal rotate-vel translate-vel)
  (type void)
  (c-set-base-rotate-velocity rotate-vel)
  (c-set-base-rotate-velocity rotate-vel))
     
     And then, since transducers can't take groups directly as arguments, you probably want to wrap it in a routine that extracts the components of a motor vector group:
     
     (define-signal (drive-base motor-vector)
  (drive-base-internal (rotation-of motor-vector)
                       (translation-of motor-vector)))
     
     
   • Write a set of transducers that call each of your low-level routines to poll each of your sensors.  The transducer should return the current value of the sensor.  E.g.:
     
     (define-transducer (current-sonar-readings)
  (type (vector integer 16))
  (state-variables (readings (make-vector 16 0)))
  (c-get-sonar-readings readings)
  readings)
     
   • Optionally, define a signal or signals to hold the current values of the sensor data:
     
     (define-signal sonar-readings (current-sonar-readings))

   • You probably want to use something better than printf for debugging.  Look at the NWU documentation on status display transducers like blink-events and display-signal for ideas.