Path: utzoo!utgpu!water!watmath!clyde!att!ihuxz!burris
From: burris@ihuxz.ATT.COM (Burris)
Newsgroups: comp.sys.atari.st
Subject: Re: MIDI Interrupts
Message-ID: <3478@ihuxz.ATT.COM>
Date: 8 Oct 88 15:19:58 GMT
References: <8810060809.AA13023@ucbvax.Berkeley.EDU>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 46

> 
> Perhaps somebody has an answer to the following:
> 
> XBIOS  function Kbdvbase()  returns a  pointer  to a  structure where  -
> among  others  -  three pointers  (*kb_midisys)(),  (*kb_vmiderr)()  and
> (*kb_midivec)() are stored.  As far as I know from  several books on the
> ATARI ST, kb_midisys() is called, when  an interrupt has occured (in one
> of the ACIAs),  kb_vmiderr() is the MIDI error  handler and kb_midivec()
> is responsible for  receiving a byte from the MIDI  port. But I couldn't
> find any further  description of what the routines should do EXACTLY and
> when/how  they are  called.

> Is there  some sort of  "official", detailed and  reliable documentation
> of  these (and  possibly other)  routines and  TOS pecularities?  Is the
> documentation, if any, available to "normal" users? Where? In W-Germany?
> 


Actually the routine is like this:

struct	vectors
{
	long	midivec;	/* MIDI input */
	long	vkbderr;	/* Keyboard error */
	long	vmiderr;	/* MIDI error */
	long	statvec;	/* IKBD status */
	long	mousevec;	/* Mouse routines */
	long	clockvec;	/* clock time routine */
	long	joyvec;		/* joystick routines */
	long	midisys;	/* system MIDI vector */
	long	ikbdsys;	/* IKBD system vector */
};

struct	vectors *kbdvbase();

midivec is the interrupt vector for the MIDI receiver. Essentially,
it just calls a routine that stores the MIDI bytes in a circular
buffer that is then read by the conin() BIOS routine.

The vmiderr vector is called whenever an overrun of the buffer is
detected.

You can supply your own MIDI interrupt routine by writing a new vector
to midivec. You should not mess with midisys.

Dave Burris