Xref: utzoo comp.os.os9:283 comp.sys.m6809:967
Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!claris!apple!voder!wlbr!pete
From: pete@wlbr.EATON.COM (Pete Lyall)
Newsgroups: comp.os.os9,comp.sys.m6809
Subject: Re: MIDI Interface driver for CoCo 3
Keywords: OS-9, Driver, MIDI
Message-ID: <24727@wlbr.EATON.COM>
Date: 30 Nov 88 22:23:15 GMT
References: <37148@clyde.ATT.COM>
Reply-To: pete@wlbr.eaton.com.UUCP (Pete Lyall)
Organization: Eaton IMSD, Westlake Village, CA
Lines: 28

Re: coco 3, OS9 LII, and MIDI - 

Kent Meyers and I attempted to adapt an existing 6850 ACIA driver to 
work with the COCO MIDI 2 pak (a 6850 UART - I forget the address, but
*think* it's $FF60 or $FF66). It works, but *not* for steady stream
data, as you would likely want for handling a sequencer's type of
operations.

Two basic but mortal problems:

a) The F$move call which is used extensively in the system blocks
interrupts. It moves 64 bytes at a whack, then lets interrupts in. It
continues this cycle until all bytes are moved from the source to 
destination memory maps. We tried reducing the number of bytes moved
to as low as 8. This helps, but didn't prevent data loss.

b) The screen scroll routines lock interrupts as well. These are more
severe, and can block for up to 500-600 microsends. Ouch. No easy 
solution here unless you suspend screen I/O while recording, or
something similar.

Pete


-- 
Pete Lyall (OS9 Users Group VP)|  DELPHI: OS9UGVP  |  Eaton Corp.(818)-706-5693
Compuserve: 76703,4230 (OS9 Sysop) OS9 (home): (805)-985-0632 (24hr./1200 baud)
Internet: pete@wlbr.eaton.com            UUCP: {hacgate,jplgodo,voder}!wlbr!pete