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From: grr@cbm.UUCP (George Robbins)
Newsgroups: net.arch
Subject: Re: Timing loops (H/W vs. S/W design)
Message-ID: <25@cbm.UUCP>
Date: Tue, 4-Mar-86 12:34:49 EST
Article-I.D.: cbm.25
Posted: Tue Mar  4 12:34:49 1986
Date-Received: Sat, 15-Mar-86 01:37:37 EST
References: <156@motatl.UUCP> <530@hoptoad.uucp> <613@sauron.UUCP> <566@hoptoad.uucp> <618@sauron.UUCP>
Organization: Commodore Engineering, West Chester, PA
Lines: 34

In article <566@hoptoad.uucp> gnu@hoptoad.uucp (John Gilmore) writes:
>In article <613@sauron.UUCP>, campbell@sauron.UUCP (Mark Campbell) writes:
>
> [Fundamental H/W realities...]
>

>> The use of the term "particularly good" when referring to a device with
>> a major flaw such as this is a non sequiteur.
>
>The Z8530 *is* a particularly good chip.  [...]

Speaking of moot problems, the recovery time specification for the Z8530 is
a non-problem in most applications.  The data sheet basically specifies that
so many PCLK cycles must elapse between accesses.  Unless you are using an
unusually slow PCLK, the overhead of the C style inb()/outb() subrountine calls
will eat up the requisite cycles.  Assembly code may need a nop or two to
guarentee cycles.

To avoid interrupt hassles, you can define C routines outoutb() and outinb()
that save interrupt status, off interrupts, write pointer, nop, read/write data,
and restore interrupts.

Also, the DMA status pins can be used to generate hardware wait states or be
sensed by software (through some other chip) to indicate when the chip is ready
to accept another operation.

The real hardware world is full of these little kludges in much the same sense
as unix is blessed with features and warts.  The 8530 does just about anything
you would want a serial interface to do, short of ethernet, and does it for two
channels.  Neither is perfect, but they let you get the job done.
-- 
George Robbins - now working with,	uucp: {ihnp4|seismo|caip}!cbm!grr
but no way officially representing	arpa: cbm!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)