Fortran Library

[ivan-pi]

When posting to Fortran Discourse I mentioned the possibility of creating a small Fortran-like language and runtime library: https://fortran-lang.discourse.group/t/fortran-chip-8-interpreter/6772/5?u=ivanpribec

Programmers could develop/test in Fortran, and then compile to CHIP-8.

The runtime library can be shared with emulator:

• drawing sprites to the screen
• clearing the screen
• setting the sound and delay timers
• checking for key presses
• converting an integer to a binary-coded decimal

Since Fortran nowadays is usually hosted on top of the C platform, it is possible to "hack" the Fortran initialization to inject additional setup procedures (e.g. turning on a screen and connecting the keyboard): https://fortran-lang.discourse.group/t/initializing-global-module-variable-object/5899/6?u=ivanpribec

We could also have a F77 like library of external routines:

C runtime routines
      external draw, clear, sound, delay, press, bcd, irand

The following target can be used to play with the idea:

C JUMPING X AND O
C
C A CHIP8 PROGRAM, ORIGINALLY BY HARRY KLEINBERG
C                                RCA CORPORATION, 1978
C
C REWRITTEN IN F77, IN 2023, BY IVAN PRIBEC
C
      PROGRAM JUMPING_X_AND_O
      INTEGER*1 XS(5),OS(5),BS(6)
C SPRITE DATA
      DATA XS,OS,BS/
     *  Z'88',Z'50',Z'20',Z'50',Z'88',
     *  Z'F8',Z'88',Z'88',Z'88',Z'F8',
     *  6*Z'FC'/
C SUBROUTINES USED
      EXTERNAL DRAW, JUMP
C START PROGRAM
      CALL DRAW(48,4,BS,6)
   10 CALL JUMP(XS,5)
      CALL JUMP(OS,5)
      GO TO 10
      END
C
C RANDOMLY DRAW A PATTERN, UNTIL IT OVERLAPS WITH THE BLOCK
C
      SUBROUTINE JUMP(PTRN,N)
      INTEGER*1 PTRN(*), N
      INTEGER*1 X, Y, K
      LOGICAL*1 OVRLPS
      INTEGER*1 IRAND
      EXTERNAL DRAW, DELAY, TIMER, IRAND
      X = 30
      Y = 13
C START JUMPING AROUND
   10 CALL DRAW(X,Y,PTRN,N,OVRLPS)
C
C COUNT DOWN DELAY TIMER
C DELAY TIMER CAN BE FOUND AT UNIT=33
C
      WRITE (33) 12
   20 READ (33) K
      IF (K > 0) GO TO 20
C IF PATTERN OVERLAPS WITH BLOCK, WE SWITCH
      IF (OVRLPS) GO TO 30
C
C ERASE PATTERN, SO WE CAN REDRAW AT NEW COORDINATES
C
      CALL DRAW(X,Y,PTRN,N)
      X = IRAND(Z'3F') ! 6-BIT RANDOM NUMBER [0, 63]
      Y = IRAND(Z'1F') ! 5-BIT RANDOM NUMBER [0, 31]
      GO TO 10
C
C ERASE PATTERN AND RETURN
C
   30 CALL DRAW(X,Y,PTRN,N)
      RETURN
      END