Difference between revisions of "Forth"

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

Revision as of 07:01, 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it online [1] and read about Forth itself here [2] (Beware that the Forth dialect in the book Starting Forth is a bit outdated compared to Atlast Forth).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 press enter and all leds should go on. Type leds off and they should go off again.