Subject: /dev/audio support for apple2 and xapple2-80col
From: munafo@gcctech.com
Newsgroups: comp.emulators.apple2
Date: Wed, 11 Oct 2000 00:33:20 GMT
Organization: Deja.com - Before you buy.
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In brief: much better audio for "xapple2" Linux Apple II emulator, at
http://www.mrob.com/xapple2

I have recently begun preparing for my "1000-to-1 party" celebrating the
fact that computers are now 1000 times faster (1 GHz) than when I
started programming the Apple ][ (1 MHz) back in 1980. (See
http://www.mrob.com/1000to1.html )

Since I'm a Linux user, and all my software was written on an Apple ][+,
I chose the "xapple2" emulator. I couldn't get the "PC speaker" sound to
work -- so I added support for /dev/audio (sound card).

The result is perfect sound reproduction (as I have verified with my
real Apple //c). It also has a very nice side-effect that if you are
running the emulator at full speed (via the F9 key), it will slow down
to genuine 1-MHz Apple ][ speed as soon as it plays sound, then speed up
again only after sound has stopped for at least 1/2 second. Thus, there
is no need to waste processor bandwidth in the speed delay loop just to
get the sound to be right.

The changes involved modifying the core CPU opcode routines (the x86
assembler code in cpu.S) to count clock cycles, and a small callback
routine for the $C030 memory access vector that does the actual writing
to /dev/audio.

I haven't seen much discussion of the xapple2 emulator recently, and the
maintainer's email address isn't working, so I'm posting this message to
let people know about it.

The changed source files are applied to the 0.7.4 release (the latest I
could find) and available at http://www.mrob.com/xapple2/

- Robert Munafo
  Apple ][ programmer since 1980


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