From IntelliWiki

These utility macros provide shorthand ways of accessing PSG registers and for converting between frequencies and period values. The source is heavily commented, serving as its documentation.

Source Code

;; ======================================================================== ;;
;;  PSG.MAC                                             Default Macro Set   ;;
;;  Joseph Zbiciak <intvnut AT gmail.com>                                   ;;
;;  These macros are hereby released into the Public Domain.                ;;
;; ======================================================================== ;;

    IF NOT DEFINED _PSG_MAC
_PSG_MAC EQU 1

;; ======================================================================== ;;
;;  Write 'r' to channel 'c', where c == 0 to 3.  Channel 3 is the          ;;
;;  envelope period "channel".  MVOPSG0 writes to PSG #0 in the             ;;
;;  Intellivision.  MVOPSG1 writes to PSG #1 in the ECS.                    ;;
;; ======================================================================== ;;
MACRO   MVOPSG0 r, c                    ; PSG inside Intellivision
        MVO     %r%, $1F0 + %c%
        SWAP    %r%
        MVO     %r%, $1F4 + %c%
ENDM

MACRO   MVOPSG1 r, c                    ; PSG inside ECS
        MVO     %r%, $0F0 + %c%
        SWAP    %r%
        MVO     %r%, $0F4 + %c%
ENDM

;; ======================================================================== ;;
;;  Like MVOPSG0, MVOPSG1, but instead takes pointer value in register 'p'. ;;
;;  note that 'p' is assumed to be an auto-incrementing pointer.  This      ;;
;;  macro leaves 'p' pointing at the next channel.                          ;;
;; ======================================================================== ;;
MACRO   MVOPSG@ r, p
        MVO@    %r%, %p%
        SWAP    %r%
        ADDI    #3,  %p%
        MVO@    %r%, %p%
        SUBI    #4,  %p%
ENDM



;; ======================================================================== ;;
;;  Read channel 'c' of PSG #0 into 'r', where c == 0 to 3.                 ;;
;; ======================================================================== ;;
MACRO   MVIPSG0 c, r
        MVI     $1F4 + %c%, %r%
        SWAP    %r%
        XOR     $1F0 + %c%, %r%
ENDM

;; ======================================================================== ;;
;;  Read channel 'c' of PSG #1 into 'r', where c == 0 to 3.                 ;;
;; ======================================================================== ;;
MACRO   MVIPSG1 c, r
        MVI     $0F4 + %c%, %r%
        SWAP    %r%
        XOR     $0F0 + %c%, %r%
ENDM

;; ======================================================================== ;;
;;  Like MVIPSG0, MVIPSG1, but instead takes pointer value in register 'p'. ;;
;;  note that 'p' is assumed to be an auto-incrementing pointer.  This      ;;
;;  macro leaves 'p' pointing at the next channel.                          ;;
;; ======================================================================== ;;
MACRO   MVIPSG@ p, r
        ADDI    #4,     %p%
        MVI@    %p%,    %r%
        SWAP    %r%
        SUBI    #5,     %p%
        XOR@    %p%,    %r%
ENDM

;; ======================================================================== ;;
;;  Calculate a period from a frequency...                                  ;;
;; ======================================================================== ;;
MACRO   tone_period_NTSC(f)
        (3579545/((32)*(%f%)))
ENDM
MACRO   tone_period_PAL(f)
        (4000000/((32)*(%f%)))
ENDM
MACRO	envp_period_NTSC(f)
        (3579545/((512)*(%f%)))
ENDM
MACRO   envp_period_PAL(f)
        (4000000/((512)*(%f%)))
ENDM

    ENDI

;; ======================================================================== ;;
;;  End of File:  psg.mac                                                   ;;
;; ======================================================================== ;;