Difference between revisions of "Forth"

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m (Adding new words)
m (Play with it)
Line 103: Line 103:
: leds 25 24 23 22 21 18 17 11 10 9 8 7 ;
: leds 25 24 23 22 21 18 17 11 10 9 8 7 ;
: ledon 12 0 do 1 setio loop ;
: on 12 0 do 1 setio loop ;
: ledoff 12 0 do 0 setio loop ;
: off 12 0 do 0 setio loop ;
Now type: leds ledon and all leds should go on. Type leds ledoff and they should go off again.
Now type: leds on and all leds should go on. Type leds off and they should go off again.

Revision as of 06:59, 7 July 2013

Forth on RPi

sudo apt-get install wget
wget http://www.fourmilab.ch/atlast/download/1.2/atlast-1.2.tar.gz
tar -xzvf atlast-1.2.tar.gz
cd atlast-1.2/

Start the Forth interpreter with ./atlast and exit with Ctrl-D

atlast.html and atlast.pdf is included and an is an extensive atlast-forth manual. Read it online [1] and read about Forth itself here [2] (Beware that the Forth dialect in the book Starting Forth is a bit outdated compared to Atlast Forth).

Adding new words

Most of the power of Atlast derives from the ease with which C coded primitives can be added to the language. In my case I will add some words for controlling my Gertboard. There is a detailed description on how to do this in the atlast-forth manual. And you can copy much of the word implementations from the gertboard_sw directory if you have downloaded the gertboard demo files. It is easy to add your own words, just add a "define GERTBOARD" to atlast.c around line 56.

#define EVALUATE                      /* The EVALUATE primitive */
#define FILEIO                        /* File I/O primitives */
#define GERTBOARD                     /* Gertboard functions */

Include the gb_common.h right after include <math.h>

#ifdef MATH
#include <math.h>

#include "gb_common.h"

Then add your own word definitions at the end of the section with word definitions, around line 2704, right after #endif /* COMPILERW */ in atlast.c


prim P_gert_setport() // channel state ---
{ // Set a digital io port to a specified state
  int rev;
  // Map the I/O sections
  if (S1 > 25)
    trouble("Max GPIO is 25");
  if (S1 == 21)
    { // first find out which rev of RPi we have
      rev = pi_revision();
      if (rev != 1)
        // GP21 on Gertboard is controlled by GPIO27
        S1 = 27;
  if (S0 == 1)
    GPIO_SET0 = (1<<S1);
    GPIO_CLR0 = (1<<S1);

prim P_gert_getport() // channel  ---
{ // Get the state of a digital port
   Sl(1); // Make sure there is at least one param on the stack
	// Your code goes here

#endif /* GERTBOARD */

And finally, add the actual words to the Table of primitive words, right after #endif /* EVALUATE */ at line 2960 or so.

    {"0EVALUATE", P_evaluate},
#endif /* EVALUATE */

	 {"0SETIO", P_gert_setport},	
	 {"0GETIO", P_gert_getport},		
#endif /* GERTBOARD */

As we are using code from the Gertboard demos, copy the files gb_common.o and gb_common.h from the gertboard_sw directory to atlast-1.2 directory (it's there if you have run make in this directory as well).

Add gb_common.o to the file Makefile in atlast-1.2.

ATLOBJ = atlast.o gb_common.o atlmain.o

Now, save and run "make" again to recompile atlast.c.

Test the new word

Wire up the Gertboard according to the information you get when you run the command sudo ./leds in the Gertboard demo directory.

Run sudo ./atlast in the atlast-1.2 directory.

Type 22 1 setio and press enter, the corresponding LED will go on.

Type 22 0 setio and the LED will go off.

Play with it

Define your own LED demo, start the interpreter with sudo ./atlast. Define three words:

: leds 25 24 23 22 21 18 17 11 10 9 8 7 ;
: on 12 0 do 1 setio loop ;
: off 12 0 do 0 setio loop ;

Now type: leds on and all leds should go on. Type leds off and they should go off again.