Program Casey_Music;

uses crt;

Const
  GMPort        = $331;
  Send          = $80;
  Receive       = $40;

{ AL:=Command; }
Procedure WriteGMCommand; Assembler;
ASM
    MOV   DX,GMPort                   {;DX:=GMStatusPort;                 }
    PUSH  AX                          {;Save AX                           }
    XOR   AX,AX                       {;AH:=TimeOutValue;                 }
@@WaitLoop:
    { ;Prevent Infinite Loop with Timeout }
    DEC   AH                          {; |If TimeOutCount=0 then          }
    JZ    @@TimeOut                   {;/   TimeOut;                      }
    {; Wait until GM is ready }
    IN    AL,DX                       {; |If Not Ready then               }
    AND   AL,Receive                  {; |  WaitLoop;                     }
    JNZ   @@WaitLoop                  {;/                                 }
@@TimeOut:
    POP   AX                          {;Restore AX                        }

    OUT   DX,AL                       {;Send Data                         }
End;

{ ; AL:=Data }
Procedure WriteGM; Assembler;
ASM
    MOV   DX,GMPort                   {;DX:=GMStatusPort;                 }
    PUSH  AX                          {;Save AX                           }
    XOR   AX,AX                       {;AH:=TimeOutValue;                 }
@@WaitLoop:
    { ; Prevent Infinite Loop with Timeout }
    DEC   AH                          {; |If TimeOutCount=0 then          }
    JZ    @@TimeOut                   {;/   TimeOut;                      }
    { ; Wait until GM is ready }
    IN    AL,DX                       {; |If Not Ready then               }
    AND   AL,Receive                  {; |  WaitLoop;                     }
    JNZ   @@WaitLoop                  {;/                                 }
@@TimeOut:
    POP   AX                          {;Restore AX                        }

    DEC   DX                          {;DX:=DataPort                     }
    OUT   DX,AL                       {;Send Data                        }
End;

{ ;Returns Data }
Function ReadGM:Byte; Assembler;
ASM
    MOV   DX,GMPort                   {;DX:=GMStatusPort;                 }
    PUSH  AX                          {;Save AX                           }
    XOR   AX,AX                       {;AH:=TimeOutValue;                 }
@@WaitLoop:
    { ; Prevent Infinite Loop with Timeout }
    DEC   AH                          {; |If TimeOutCount=0 then          }
    JZ    @@TimeOut                   {;/   TimeOut;                      }
    { ; Wait until GM is ready }
    IN    AL,DX                       {; |If Not Ready then               }
    AND   AL,Send                     {; |  WaitLoop;                     }
    JNZ   @@WaitLoop                  {;/                                 }
@@TimeOut:
    POP   AX                          {;Restore AX                        }

    DEC   DX                          {;DX:=DataPort                      }
    IN    AL,DX                       {;Receive Data                      }
End;

Procedure ResetGM; Assembler;
ASM
    { ;Reset GM }
    MOV   DX,GMPort
    MOV   AL,0FFh
    OUT   DX,AL
    {; Get ACK }
    CALL  ReadGM
    {; UART Mode }
    MOV   AL,03Fh
    CALL  WriteGMCommand
End;

Procedure SetNoteOn(Channel,Note,Volume:Byte); Assembler;
ASM
    MOV   AL,[Channel]
    ADD   AL,90h
    Call  WriteGM
    MOV   AL,[Note]
    CALL  WriteGM
    MOV   AL,[Volume]
    CALL  WriteGM
End;

Procedure SetNoteOff(Channel,Note,Volume:Byte); Assembler;
ASM
    MOV   AL,[Channel]
    ADD   AL,80h
    Call  WriteGM
    MOV   AL,[Note]
    CALL  WriteGM
    MOV   AL,[Volume]
    CALL  WriteGM
End;

var
     note:char;

Begin
  writeln ('Press esc to quit ...');
  repeat
  note:=readkey;
  ResetGM;
  SetNoteOn(0,ord(note)-64,127);
  SetNoteOff(0,ord(note)-64,127);
  ResetGM;
  until note = #27;
End.