AI That Plays Melodies

Now that I was able to generate note messages, I asked ChatGPT to create a program that plays a melody.

I followed these steps to make the request:

1. As in the previous attempt, I asked ChatGPT to generate a program in Z80 assembler to produce note signals. This time, I specified both the address of the ACIA status register and the data register.
2. Since the A register was being overwritten in the MIDI transmission subroutine, I asked ChatGPT to fix this issue.
3. I requested a modification to store the pitch information in a table format.
4. I then asked ChatGPT to generate the pitch sequence for "Greensleeves" in the table. (It seems that ChatGPT couldn’t generate it correctly.)
5. Since the instruction IN A, (B) was being generated, I requested a correction.

With these steps, the assembler program was created, which I downloaded to my computer and generated a HEX file. Although it wasn’t "Greensleeves," I was able to play some melody.

https://chatgpt.com/share/67026d7d-ab60-8003-9f54-4ff0b840cc6b

    ORG $8000           ; Program starts at address $8000

START:
    LD HL, NOTE_TABLE   ; Point HL to the start of the note table

NEXT_NOTE:
    LD A, (HL)          ; Load the next note number from the table
    CP 0                ; Check if the note number is 0 (end of the table)
    JR Z, DONE          ; If 0, end the program

    CALL SEND_NOTE_ON   ; Send Note-On message for this note
    CALL LONG_DELAY     ; Long delay before sending Note-Off
    CALL SEND_NOTE_OFF  ; Send Note-Off message for this note

    INC HL              ; Move to the next note in the table
    JR NEXT_NOTE        ; Repeat for the next note

DONE:
    RET                 ; Return to the caller when done

; Subroutine to send a Note-On message
SEND_NOTE_ON:
    LD A, $90           ; Load Note-On status byte (channel 1, note-on)
    CALL SEND_MIDI      ; Send the status byte

    LD A, (HL)          ; Load the note number from the table
    CALL SEND_MIDI      ; Send the note number

    LD A, $7F           ; Load velocity (127, maximum)
    CALL SEND_MIDI      ; Send the velocity
    RET                 ; Return to the main routine

; Subroutine to send a Note-Off message
SEND_NOTE_OFF:
    LD A, $80           ; Load Note-Off status byte (channel 1, note-off)
    CALL SEND_MIDI      ; Send the status byte

    LD A, (HL)          ; Load the note number from the table
    CALL SEND_MIDI      ; Send the note number

    LD A, $00           ; Load velocity (0, note-off)
    CALL SEND_MIDI      ; Send the velocity
    RET                 ; Return to the main routine

; Subroutine to send a MIDI byte, preserving A
SEND_MIDI:
    PUSH AF             ; Preserve register A by pushing AF to the stack
WAIT_READY:
    IN A, ($A0)         ; Read the status register from address $A0
    BIT 1, A            ; Check if transmit data register empty (bit 1 = 1)
    JR Z, WAIT_READY    ; Wait until the data register is ready

    POP AF              ; Restore A from the stack
    OUT ($A1), A        ; Send the byte to the data register at address $A1
    RET                 ; Return to the main routine

; Long delay routine (for longer duration between notes)
LONG_DELAY:
    LD BC, $FFFF        ; Load a larger value into BC for longer delay
DELAY_LOOP:
    DEC BC              ; Decrement BC
    LD A, B             ; Check upper byte
    OR C                ; Combine upper and lower bytes
    JR NZ, DELAY_LOOP   ; Continue looping until BC = 0
    RET                 ; Return after delay

; Data table of MIDI note numbers for "Greensleeves" melody (0 terminates the table)
NOTE_TABLE:
    DB $40, $43, $45, $47, $45, $43, $40   ; A3, C#4, E4, F#4, E4, C#4, A3
    DB $40, $43, $45, $47, $45, $43, $40   ; Repeat similar phrase
    DB $45, $47, $48, $47, $45, $43, $40   ; E4, F#4, G#4, F#4, E4, C#4, A3
    DB 0                                   ; End of the table