A Midi Demo for the Mac II

By Kirk Austin, Contributing Editor, San Rafael, CA

Here we are back in MIDI land again. This is a continuation of the July 1987 article in which we bacame familiar with what MIDI is all about, and looked into some of the low level routines that are necessary to work with MIDI on the Macintosh.

Now, probably what I didn’t tell you last time was that these low level routines were designed to work with LightSpeed Pascal from Think Technologies. I have found that this is the easiest development system for people just starting to program the Macintosh because of its unique source level debugging features. Also, I have found the Pascal language to be the best choice among languages available for the Macintosh because the Macintosh was designed with the Pascal language in mind. Because of this all of the documentation is written with a Pascal syntax (Inside Macintosh, Macintosh Revealed, etc.).

As a result of this built-in bias, if any other language than Pascal is chosen as a development tool, a great deal of time is typically spent just translating from the Pascal documentation to whatever language you have decided to use. The moral of the story is, if you are just starting out programming the Macintosh, you would be doing yourself a big favor by choosing Pascal as your development language, ‘nuff said.

The Apple Music Fair

On July 10th Apple had an in-house party to let its employees find out more about music programs for the Macintosh. It was a great party, with food and drinks in the courtyard of the DeAnza 3 building. About a dozen or so companies with music products for the Macintosh were present, showing their wares, and there was even a presentation by Alan Kay on the future of computers and music.

I was impressed by the fact that Apple is making an effort to get its employees excited about the musical possibilities of the Macintosh computer. The Mac has become the defacto standard for MIDI controllers. If you attend one of the biannual NAMM shows (which is where all of the new musical products are exhibited) you will find that the Macintosh has taken over as far as musical computers go. I just wish Apple would go a little bit further with their support of MIDI. For instance, I know that there are MIDI routines built into the new ROM’s on the Macintosh II, but I can’t get anyone at Apple to tell me what they are. Now, obviously, someone there knows what the routines are, after all, someone had to write them in the first place, right? But, for some reason, Apple is not releasing the information just yet. I hope this changes soon, as I would like to be using ROM routines instead of having to write all of my own code, but I guess I will just have to wait a while (sigh).

By the way, I heard that copies of the July issue of MacTutor are making the rounds at Apple and I have gotten inquiries about the MIDI routines from some Apple employees. Maybe I can stir up enough interest at Apple to get them to come through with some information (are you listening, guys?).

Whoops!

Unfortunately, there was a slight oversight on my part in the program listings that were printed in July that caused a bug in the interrupt handlers. If you are using the low level routines in a program that uses input from the Macintosh keyboard, the status register can become corrupted by the MIDI interrupt routines and the computer will think that it is getting a never-ending string of keystrokes from the ASCII keyboard. I get a string of lower case “c”, but othere people have reported getting lower case “s”.

Anyway, the problem is that I neglected to save and restore the status register in the interrupt routines, so you need to add the following two lines to the four interrupt handlers (i.e. TxIntHandA, TxIntHandB, RxIntHandA, and RxIntHandB):

This should be the first line at the beginning of each routine:

 MOVE  SR,-(SP)

then, replace the line

 ANDI  #$F8FF,SR

at the end of each interrupt handler with the following line

 MOVE  (SP)+,SR

This change keeps the status register intact instead of changing its value after the interrupt routine has executed. Sorry if this error has caused anyone a great deal of hair pulling.

New Changes to LLMIDI

There are also a couple of additional routines that I have added to the library since it was published. The revised routine library is available on the source code disk for July, so if you just buy that you will save yourself an awful lot of typing. Also, there is the distinct possibility that if you do type the listings in yourself that you will make a typo and it will get flagged as an assembly error. The listings on the source code disk have been assembled with MDS without any errors being flagged, so if you are showing an error it is probably a typo.

Anyway, the new additions to the library have to do with filtering out “active sensing” MIDI bytes from the data stream, and also adding a MIDI thru function that echoes the incoming MIDI data on either the same port or the opposite one.

Active Sensing

This is a data byte that is sent out by some controllers every 300 milliseconds or so that lets receiving equipment know that everything is hunky dory. Mostly, it just gets in the way of whatever you might be trying to do with the MIDI data stream, so the best thing to do is just filter it out before it gets placed in the buffer. A slight change to the RxIntHand routines is all that is necessary to do this, and it consists of a grand total of two lines of assembly code.

MIDI Thru

The MIDI thru capability is pretty easy to add too. It’s another change to the RxIntHand routines that calls either TxMIDIA or TxMIDIB depending on the variable ThruFlagA or ThruFlagB. In order to set the variables two routines had to be added to the library: MIDIThruA and MIDIThruB.

The new routines

{1}
XDEF  MIDIThruA
XDEF  MIDIThruB
ThruFlagA  DC 0  ; MIDI thru flag for modem port
ThruFlagB  DC 0  ; MIDI thru flag for printer port
 
; This routine lets you do a MIDI Thru function
; The Thrucode is:
; 0 = No thru function
; 1 = MIDI thru on the same channel
; 2 = MIDI thru on the opposite channel

; Procedure MIDIThruA(Thrucode : integer);
MIDIThruA
 LEA  ThruFlagA,A0  ; point to the flag
 MOVE  4(SP),(A0)  ; set the flag
 MOVE.L  (SP)+,A0  ; save the return address
 ADDQ  #2,SP     ; move past the parameter
 MOVE.L  A0,-(SP)  ; put the return address back
 RTS      ; and return
 
; This is the interrupt routine for receiving through the
; modem port. It places the counter value and the MIDI byte in
; a circular queue to be accessed later by the application.
; When the system gets this far, A0 contains the SCC base read
; Ctl address and A1 contains the SCC base write Ctl address
; for this channel. The data addresses are offset by 4 from 
; the control addresses. D0-D3/A0-A3 are already preserved, so 
; they may be used freely.

RxIntHandA
 MOVE  SR,-(SP)  ; save status register
 ORI  #$0300,SR  ; disable interrupts
 
@3 MOVE  #4,D0   ; get data offset
 CLR.L  D1       ; prepare for data
 MOVE.L  (SP),(SP)   ; Delay
 MOVE.B  0(A0,D0),D1    ; read data from SCC
 MOVE.L  (SP),(SP)   ; Delay
 CMPI  #$FE,D1   ; filter out acitve sensing
 BEQ  @2
 LEA  ThruFlagA,A1   ; 
 CMPI  #1,(A1)   ; check for MIDI Thru
 BNE  @4
 MOVE  D1,-(SP)  ; put data on the stack
 BSR  TxMIDIA    ; send it out port A
@4

 LEA  ThruFlagA,A1   ;
 CMPI  #2,(A1)   ; check for MIDI Thru
 BNE  @5
 MOVE  D1,-(SP)  ; put data on the stack
 BSR  TxMIDIB    ; send it out port B
@5
 LEA  RxQueueA,A2  ; point to queue
 LEA  RxByteInA,A3   ; get the address
 MOVE  (A3),D0   ; get offset to next cell
 LEA  Counter,A3   ; get the address
 MOVE.L  (A3),D2   ; put counter value in D2
 LSL.L  #8,D2    ; shift counter one byte
 ADD.L  D2,D1    ; combine counter and data
 MOVE.L  D1,0(A2,D0)    ; put longword in queue
 LEA  RxQEmptyA,A3   ; get the address
 MOVE  #0,(A3)   ; reset queue empty flag
 ADDQ  #4,D0     ; update index
 CMP  #$400,D0
 BNE  @1
 MOVE  #0,D0
@1 LEA  RxByteInA,A3      ; get the address
 MOVE  D0,(A3)
 
@2 BTST.B  #0,(A0)   ; is there more data?
 BNE  @3    ; do it again if there is
 
 MOVE  (SP)+,SR  ; restore status register
 RTS      ; and return
  
; This is the interrupt routine for transmitting a byte
; through the modem port. It checks to see if there is any 
; data to send, and if there is it sends it to the SCC.  If
; there isn’t it resets the TBE interrupt in the SCC and 
; exits. When the system gets this far, A0 contains the SCC 
; base read Ctl address and A1 contains the SCC base write Ctl 
; address for this channel. The data addresses are offset by 4 
; from the control addresses. D0-D3/A0-A3 are already pre
; served, so they may be used freely.

TxIntHandA
 MOVE  SR,-(SP)  ; save the status register
 ORI  #$0300,SR  ; disable interrupts
  
 LEA  TxQEmptyA,A3   ; get the address
 TST.B  (A3)     ; Is queue empty?
 BEQ  @1    ; if not branch
 MOVE.B  #$28,(A1)   ; if so, reset TBE interrupt
 MOVE.L  (SP),(SP)   ; Delay
 BRA  TxIExitA   ; and exit
@1 LEA  TxByteOutA,A3     ; get the address
 MOVE  (A3),D0   ; get index to next data byte
 LEA  TxQueueA,A2  ; point to queue
 MOVE  #4,D1     ; get data offset
 MOVE.B  0(A2,D0),0(A1,D1)  ; write data to SCC
 MOVE.L  (SP),(SP)   ; Delay
 ADDQ  #1,D0     ; update index
 CMP  #$100,D0
 BNE  @2
 MOVE  #0,D0
@2 LEA  TxByteOutA,A3     ; get the address
 MOVE  D0,(A3)
 LEA  TxByteInA,A3   ; get the address
 MOVE  (A3),D1
 CMP  D0,D1      ; is TxQueue empty?
 BNE  TxIExitA   ; if not exit
 LEA  TxQEmptyA,A3   ; get the address
 MOVE  #$FFFF,(A3)   ; if empty set flag
 
TxIExitA
 MOVE  (SP)+,SR  ; restore status register
 RTS      ; and return

; This routine lets you do a MIDI Thru function
; The Thrucode is:
;  0 = No thru function
;  1 = MIDI thru on the same channel
;  2 = MIDI thru on the opposite channel
; Procedure MIDIThruB(Thrucode : integer);

MIDIThruB
 LEA  ThruFlagB,A0   ; point to the flag
 MOVE  4(SP),(A0)  ; set the flag
 MOVE.L  (SP)+,A0  ; save the return address
 ADDQ  #2,SP     ; move past the parameter
 MOVE.L  A0,-(SP)  ; put the return address back
 RTS      ; and return
 
; This is the interrupt routine for receiving through the
; printer port. It places the counter value and the MIDI byte
; in a circular queue to be accessed later by the appl-
; ication. When the system gets this far, A0 contains the SCC
; base read Ctl address and A1 contains the SCC base write Ctl
; address for this channel. The data addresses are offset by 4
; from the control addresses. D0-D3/A0-A3 are already pre-
; served, so they may be used freely.

RxIntHandB
 MOVE  SR,-(SP)  ; save status register
 ORI  #$0300,SR  ; disable interrupts
  
@3 MOVE  #4,D0   ; get data offset
 CLR.L  D1       ; prepare for data
 MOVE.L  (SP),(SP)   ; Delay
 MOVE.B  0(A0,D0),D1      ; read data from SCC
 MOVE.L  (SP),(SP)   ; Delay
 CMPI  #$FE,D1   ; filter out acitve sensing
 BEQ  @2
 LEA  ThruFlagB,A1
 CMPI  #1,(A1)   ; check for MIDI Thru
 BNE  @4
 MOVE  D1,-(SP)  ; put data on the stack
 BSR  TxMIDIB    ; send it out port B
@4
 LEA  ThruFlagB,A1
 CMPI  #2,(A1)   ; check for MIDI Thru
 BNE  @5
 MOVE  D1,-(SP)  ; put data on the stack
 BSR  TxMIDIA    ; send it out port A
@5
 LEA  RxQueueB,A2  ; point to queue
 LEA  RxByteInB,A3   ; get the address
 MOVE  (A3),D0   ; get offset to next cell
 LEA  Counter,A3   ; get the address
 MOVE.L  (A3),D2   ; put counter value in D2
 LSL.L  #8,D2    ; shift counter one byte
 ADD.L  D2,D1    ; combine counter and data
 MOVE.L  D1,0(A2,D0)      ; put longword in queue
 LEA  RxQEmptyB,A3   ; get the address
 MOVE  #0,(A3)   ; reset queue empty flag
 ADDQ  #4,D0     ; update index
 CMP  #$400,D0
 BNE  @1
 MOVE  #0,D0
@1 LEA  RxByteInB,A3      ; get the address
 MOVE  D0,(A3)
  
@2 BTST.B  #0,(A0)   ; is there more data?
 BNE  @3    ; do it again if there is
 
 MOVE  (SP)+,SR  ; restore status register
 RTS      ; and return
  
; This is the interrupt routine for transmitting a byte
; through the printer port.
; It checks to see if there is any data to send, and if there
; is it sends it to the SCC.  If there isn’t it resets the TBE
; interrupt in the SCC and exits. When the system gets this
; far, A0 contains the SCC base read Ctl address and A1
; contains the SCC base write Ctl address for this channel. 
; The data addresses are offset by 4 from the control addr-
; esses. D0-D3/A0-A3 are already preserved, so they may be 
; used freely.

TxIntHandB
 MOVE  SR,-(SP)  ; save status register
 ORI  #$0300,SR  ; disable interrupts
  
 LEA  TxQEmptyB,A3   ; get the address
 TST.B  (A3)     ; Is queue empty?
 BEQ  @1    ; if not branch
 MOVE.B  #$28,(A1)   ; if so, reset TBE interrupt
 MOVE.L  (SP),(SP)   ; Delay
 BRA  TxIExitB   ; and exit
@1 LEA  TxByteOutB,A3     ; get the address
 MOVE  (A3),D0   ; get index to next data byte
 LEA  TxQueueB,A2  ; point to queue
 MOVE  #4,D1     ; get data offset
 MOVE.B  0(A2,D0),0(A1,D1)  ; write data to SCC
 MOVE.L  (SP),(SP)   ; Delay
 ADDQ  #1,D0     ; update index
 CMP  #$100,D0
 BNE  @2
 MOVE  #0,D0
@2 LEA  TxByteOutB,A3     ; get the address
 MOVE  D0,(A3)
 LEA  TxByteInB,A3   ; get the address
 MOVE  (A3),D1
 CMP  D0,D1      ; is TxQueue empty?
 BNE  TxIExitB   ; if not exit
 LEA  TxQEmptyB,A3   ; get the address
 MOVE  #$FFFF,(A3)   ; if empty set flag
 
TxIExitB
 MOVE  (SP)+,SR  ; restore status register
 RTS      ; and return

The World’s dumbest MIDI program

This brings us to an actual example of how to use these routines in a typical program. For the example program I have chosen to make the Macintosh into the worlds most expensive MIDI thru box. Actually, it reminds me of when I first got my Macintosh in 1984 with just MacPaint and MacWrite available. I used to call it the $2,000 etch-a-sketch (ha ha).

At any rate, the demo program MIDI Shell lets you test out the various modes of MIDI thru by using menu selections. I also added some of my preferred techniques for writing applications in general, such as including a Transfer... menu item in the file Menu, and using an About... dialog box that doesn’t get in the user’s way.

What I mean by that last statement is that most About... boxes that I see force you to click on an OK button or something in order to continue working in the program. Now, there are some cases where you don’t have to click in the dialog box itself, but you can’t just go up and make a normal menu selection because you have to click once just to get rid of the dialog first (the finder’s About... box is an example of this way to handle it). My feeling is that the optimum way to deal with the About... dialog box is to make it possible to use the program without having to concern yourself with getting rid of the dialog box first. This is accomplished by using the scheme presented in the DoAbout procedure.

The Transfer... item in the File menu is one that I wish were in every Macintosh program. It makes life much easier by not making the user have to go back to the Finder all the time. Considering that it is so simple to implement, I end up using it in every program I write.

More ways to skin the cat

Now, I should probably point out at this time that there are other ways to deal with MIDI input and output besides the interrupt method that I have described so far. There is also a technique known as polling.

Polling is done by dropping all other considerations and just constantly looking at the receive register of the SCC chip to see if there is anything there. While it may sound really dumb at first, polling can be very useful in certain circumstances, like when you know exactly when a large amount of MIDI data is going to arrive. This happens in programs like patch librarians, for example.

Now, of course, doing polling requires an entirely different set of low level routines. Next article I’ll show you some of these routines and how to write a simple patch librarian with them. Then, in a later article, I’ll come back to the interrupt driven library to look at writing a ‘Stone Age Sequencer’. Until then, happy coding.

{2}
{ Kirk Austin, 7/12/87 }
{ This is an example program that illustrates the } 
{following techniques: }
{ My preferred method for handling the about box }
{The use of the transfer command in the file menu }
{The use of the LSPMIDI library including MIDIThru}

PROGRAM ShellExample;

 USES
 LSPMIDI;
{ Global Constants }
 CONST
 Null = ‘’;
 AppleMenuID = 1;
 FileMenuID = 2;
 EditMenuID = 3;
 MIDIMenuID = 4;
 AboutID = 200;
{ Global Variables }
 VAR
 myMenus : ARRAY[AppleMenuID..MIDIMenuID] OF MenuHandle;
 Done : Boolean; { true when user selects quit}
{This is a way to do the about box so that it doesn’t interfere with 
the application. For instance, you can make menu selections while the 
about box is visible.}

 PROCEDURE ShowAbout;
 VAR
 theDlog : DialogPtr;
 oldPort : GrafPtr;
 BEGIN
 GetPort(oldPort);
 theDlog := GetNewDialog(AboutID, NIL, Pointer(-1));
 SetPort(theDlog);
 DrawDialog(theDlog);
 WHILE NOT Button DO
 ;
 DisposDialog(theDlog);
 SetPort(oldPort);
 END;

 PROCEDURE LaunchIt (mode : integer;
 VAR fName : Str255);
 INLINE
 $204F, {movea.l  a7,a0;(a0) is string ptr, 4(a0) mode}
 $A9F2; {_Launch}


 PROCEDURE DoXfer;
 VAR
 where : Point;
 reply : SFReply;
 vRef : integer;
 thefName : Str255;
 textType : SFTypeList;
 BEGIN
 where.h := 80;
 where.v := 55;
 textType[0] := ‘APPL’;
 SFGetFile(where, Null, NIL, 1, textType, NIL, reply);
 WITH reply DO
 IF NOT good THEN
 thefName := Null
 ELSE
 BEGIN
 thefName := fName;
 vRef := vRefNum
 END;
 IF thefName <> Null THEN
 BEGIN
 Done := true;
 IF SetVol(NIL, vRef) = noErr THEN
 BEGIN
 ResetSCCA;
 ResetSCCB;
 QuitTimer;
 LaunchIt(0, thefName)
 END;
 END
 END;

 PROCEDURE ProcessMenu ( codeWord : Longint);
 { handle menu selections}
 VAR
 i : integer;
 menuNum : Integer;
 TheMenuHdle : MenuHandle;
 itemNum : Integer;
 NameHolder : str255;
 dummy : Integer;
 ignore : boolean;
 TheValue : longint;

 BEGIN
 IF codeWord <> 0 THEN  { nothing was selected}
 BEGIN
 menuNum := HiWord(codeWord);
 itemNum := LoWord(codeWord);
 CASE menuNum OF { the different menus}
 AppleMenuID : 
 BEGIN
 IF itemNum < 3 THEN
 BEGIN
 ShowAbout;
 END
 ELSE
 BEGIN
 GetItem(myMenus[AppleMenuID], itemNum, NameHolder);
 dummy := OpenDeskAcc(NameHolder);
 END;
 END;
 FileMenuID : 
 BEGIN
 CASE ItemNum OF
 1 : 
 BEGIN
 DoXfer;
 END;
 2 : 
 BEGIN
 Done := true;
 END;
 END;
 END;
 EditMenuID : 
 BEGIN
 ignore := SystemEdit(itemNum - 1);
 END;
 MIDIMenuID : 
 BEGIN
 TheMenuHdle := GetMHandle(4);
 FOR i := 1 TO 5 DO
 CheckItem(TheMenuHdle, i, false);
 MIDIThruA(0);
 MIDIThruB(0);
 CASE ItemNum OF
 1 : 
 BEGIN
 CheckItem(TheMenuHdle, 1, true);
 MIDIThruA(1);
 END;
 2 : 
 BEGIN
 CheckItem(TheMenuHdle, 2, true);
 MIDIThruA(2);
 END;
 3 : 
 BEGIN
 CheckItem(TheMenuHdle, 3, true);
 MIDIThruB(1);
 END;
 4 : 
 BEGIN
 CheckItem(TheMenuHdle, 4, true);
 MIDIThruB(2);
 END;
 5 : 
 BEGIN
 CheckItem(TheMenuHdle, 5, true);
 MIDIThruA(0);
 MIDIThruB(0);
 END;
 END;
 END;
 END;
 HiliteMenu(0);
 END;
 END;

 PROCEDURE DealWithMouseDowns (theEvent : EventRecord);
 VAR
 location : Integer;
 windowPointedTo : WindowPtr;
 mouseLoc : point;
 windowLoc : integer;
 VandH : Longint;
 Height : Integer;
 Width : Integer;
 BEGIN
 mouseLoc := theEvent.where;
 windowLoc := FindWindow(mouseLoc, windowPointedTo);
 CASE windowLoc OF
 inMenuBar : 
 BEGIN
 ProcessMenu(MenuSelect(mouseLoc));
 END;
 inSysWindow : 
 BEGIN
 SystemClick(theEvent, windowPointedTo);
 END;
 OTHERWISE
 BEGIN
 END;
 END;
 END;

 PROCEDURE DealWithKeyDowns (theEvent : EventRecord);
 TYPE
 Trick = PACKED RECORD
 CASE boolean OF
 true : (
 long : Longint
 );
 false : (
 chr3, chr2, chr1, chr0 : char
 )
 END;
 VAR
 CharCode : char;
 TrickVar : Trick;
 BEGIN
 TrickVar.long := theEvent.message;
 CharCode := TrickVar.chr0;
 IF BitAnd(theEvent.modifiers, CmdKey) = CmdKey THEN 
 {check for a menu selection}
 BEGIN
 ProcessMenu(MenuKey(CharCode));
 END
 END;

 PROCEDURE MainEventLoop;
 VAR
 Event : EventRecord;
 ProcessIt : boolean;
 x : byte;
 TheValue : Longint;
 BEGIN
 REPEAT
 SystemTask;
 ProcessIt := GetNextEvent(everyEvent, Event); 
 { get the next event in queue}
 IF ProcessIt THEN
 BEGIN
 CASE Event.what OF
 mouseDown : 
 DealWithMouseDowns(Event);
 AutoKey : 
 DealWithKeyDowns(Event);
 KeyDown : 
 DealWithKeyDowns(Event);
 OTHERWISE
 BEGIN
 END;
 END;
 END;
 UNTIL Done;
 END;

 PROCEDURE MakeMenus;{ get the menus & display them}
 VAR
 index : Integer;
 TheMenuHdle : MenuHandle;
 BEGIN
 FOR index := AppleMenuID TO MIDIMenuID DO
 BEGIN
 myMenus[index] := GetMenu(index);
 InsertMenu(myMenus[index], 0);
 END;
 AddResMenu(myMenus[AppleMenuID], ‘DRVR’);
 DrawMenuBar;
 {put a check mark on the “none” menu item by default}
 TheMenuHdle := GetMHandle(4);
 CheckItem(TheMenuHdle, 5, true);
 END;

{ Program Starts Here }
BEGIN
 Done := false;
 FlushEvents(everyEvent, 0);

 InitSCCA;
 InitSCCB;
 InitTimer(782 * 5); 
 {increment the counter every 5 milliseconds}
 StartCounter;

 MakeMenus;
 InitCursor;
 MainEventLoop;

 ResetSCCA;
 ResetSCCB;
 QuitTimer;

END.


UNIT LSPMIDI;
{Midi library available on this source code disk for LSP }
INTERFACE
 PROCEDURE InitSCCA;
 {call this once at the beginning of your application if you are going 
to use the modem port for MIDI}

 PROCEDURE TxMIDIA (TheData : integer);
 {use this procedure to transmit a byte of MIDI data through the modem 
port the MIDI byte is in the lower 8 bits of the word}

 FUNCTION RxMIDIA : LongInt;
 {use this function to get a byte of MIDI data and the counter value 
associated with that byte through the modem port the MIDI byte is in 
the lower 8 bits of the longword the upper 3 bytes of the longword contain 
the counter value when the byte arrived at the Macintosh}

 PROCEDURE MIDIThruA (Thrucode : integer);
 {this is for the MIDI thru function}
 {the Thrucode variable is as follows:}
 {0 = no MIDIThru function}
 {1 = MIDIThru on the same channel}
 {2 = MIDIThru on the opposite channel}

 PROCEDURE ResetSCCA;
 {call this procedure when your application is done if you called InitSCCA 
at the beginning of your application or the system will crash}

 PROCEDURE InitSCCB;
 {call this once at the beginning of your application if you are going 
to use the printer port for MIDI}

 PROCEDURE TxMIDIB (TheData : integer);
 {use this procedure to transmit a byte of MIDI data through the printer 
port the MIDI byte is in the lower 8 bits of the word}

 FUNCTION RxMIDIB : LongInt;
 {use this function to get a byte of MIDI data and the counter value 
associated with that byte through the printer port the MIDI byte is in 
the lower 8 bits of the longword the upper 3 bytes of the longword contain 
the counter value when the byte arrived at the Macintosh}

 PROCEDURE MIDIThruB (Thrucode : integer);
 {this is for the MIDI thru function}
 {the Thrucode variable is as follows:}
 {0 = no MIDIThru function}
 {1 = MIDIThru on the same channel}
 {2 = MIDIThru on the opposite channel}

 PROCEDURE ResetSCCB;
 {call this procedure when your application is done if you called InitSCCB 
at the beginning of your application or the system will crash}

 PROCEDURE InitTimer (TimrValue : integer);
 {call this procedure once at the beginning of your application if you 
are going to make use of time-stamping.  1 millisecond = decimal 782}

 PROCEDURE LoadTimer (TimrValue : integer);
 {call this procedure if you want to change the interval of time that 
the counter is incremented.  1 millisecond = decimal 782}

 PROCEDURE StartCounter;
 {call this procedure to set the counter value to 1}

 FUNCTION GetCounter : LongInt;
 {call this function to get the current value of the counter}

 PROCEDURE QuitTimer;
 {call this procedure when your application is done if you called InitTimer 
at the beginning of your application or the system will crash}

IMPLEMENTATION
{$A+}
 PROCEDURE InitSCCA;
 external;
 PROCEDURE TxMIDIA;
 external;
 FUNCTION RxMIDIA;
 external;
 PROCEDURE MIDIThruA;
 external;
 PROCEDURE ResetSCCA;
 external;
 PROCEDURE InitSCCB;
 external;
 PROCEDURE TxMIDIB;
 external;
 FUNCTION RxMIDIB;
 external;
 PROCEDURE MIDIThruB;
 external;
 PROCEDURE ResetSCCB;
 external;
 PROCEDURE InitTimer;
 external;
 PROCEDURE LoadTimer;
 external;
 PROCEDURE StartCounter;
 external;
 FUNCTION GetCounter;
 external;
 PROCEDURE QuitTimer;
 external;
{$A-}

END.