Newsgroups: comp.sys.amiga.audio
Path: utzoo!utgpu!cunews!ags
From: ags@scs.carleton.ca (Alexander G. M. Smith)
Subject: Re: CHEAP 16-bit STEREO sound samplers
Message-ID: <1991Jun17.150054.27117@cunews.carleton.ca>
Sender: news@cunews.carleton.ca
Organization: School of Computer Science, Carleton University, Ottawa, Canada
References: <91166.165734DXB132@psuvm.psu.edu> <39yN41w164w@bluemoon.uucp>
Date: Mon, 17 Jun 1991 15:00:54 GMT

In article <39yN41w164w@bluemoon.uucp> moonhawk@bluemoon.uucp (David Culberson) writes:
>DXB132@psuvm.psu.edu writes:
>
>> Mybe it's time for the $50 PD hack 16-bit audio board. :-)
>
>        You know, I AM working on one! ...
>... does anyone know how much the Amiga's parallel port is 
>capable of handling? As in,  how many Kilo/Mega bytes per second? I migh 
>have to restrict it to 4 channel 8 bit and 2 channel 16 bit if I go 
>through the parallel port, and I want to; I donn't know ANYHTING about the 
>Zorro II bus specs! SO, Could the Parallel port handle, say, 8 8-bit 
>DAC's going at approk. 44kHz?? Or, the same number would be 4, 16 bit  
>DAC's going at 44kHz? I don't think so, but I HOPE I am wrong; it would be 
>very impressive. Bye!

The parallel port can go very fast, assuming that it is like the old CIA
chips in the C64, at least a megahertz (one million read a byte
operations per second).  The bottleneck seems to be more with the
software reading from it (unless you are using an A3000).  Figure that
you have to toggle a control line to pick which half of 16 bits is read
/ latched: 2 instructions per word read.  Then there's the reading,
another two instructions.  Storage takes another three, two for mixing
the bytes into a word and one for saving and incrementing the storage
pointer.  Another two are needed for testing if you have filled your
recording buffer.  So, that's 9 instructions per word.  Each instruction
takes, what, 4 clock cycles (one or two to read the op code, another
couple to read or write the data).  So, that's ballpark 40 clock cycles. 
On an 8MHz machine, that's 200,000 word size samples per second. 

Of course, if your hardware handshaking gets complicated, it will slow
things down. 

- Alex
