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From: koonce@brahms.berkeley.edu (tim koonce)
Newsgroups: comp.os.os9,comp.sys.m6809
Subject: Re: Adapting coco OS9 to other systems
Keywords: OS9, coco III, uniboard
Message-ID: <22256@agate.BERKELEY.EDU>
Date: 29 Mar 89 19:05:41 GMT
References: <386@aucis.UUCP> <989@mcrware.UUCP> <388@aucis.UUCP> <992@mcrware.UUCP> <391@aucis.UUCP>
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Reply-To: koonce@math.berkeley.edu (tim koonce)
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Organization: University of California, Berkeley
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Jeff Easton writes:
>> Tim Koonce writes:
>>The big hassle with getting it running will be interrupts.
>Hmmm,  My 6522 has two 16 bit timers.  With a E clock at 2 Mhz, /65535 
>yielding a maximum of 30.5 Hz or 32.8 mSec between IRQ's (not the FIRQ).
>so far, so good...
You will have to hack the boot code to set up that timer properly, but
that shouldn't be too hard.

>Okay, but does version 2.0 (not level II) buy me anything?  Is it a bug
>fix release?  Will 2.0 run on a coco 1 or 2? (assuming I scrap up a coco 1
>or 2 to port it on).  I would like to get the best version possible.
ver. 2.0 of Level I will definitely run on a CoCo 1 or 2.  It changes a
few things, but mostly it includes a few new utilities, and some new drivers.
Nothing which is particularly interesting for your project, but some of
it might be nice to get eventually.

>One other question, do I need DMA for the disk transfers?  My board has
>a 6844 DMA chip but I confess, I've never used it.
The CoCo floppy I/O code uses the processor to supervise the transfer.
It requires that the 1773/1793 FDC chip be connected to the processor
Halt line.  The basic idea is that the processor runs a tight loop
transferring data from the FDC, and the FDC halts the processor until
the next byte is ready.  It wreaks havoc with multi-user systems, since
sector transfers are non-interruptable, but works fine for single-user
stuff.  While you're hacking drivers, though, putting together a floppy
driver to use that DMA chip might be nice.  The biggest practical problem
with the CoCo Level 1 floppy driver is simply that it's hard-coded for
35 track single-sided operation, which is a pain.  D.P. Johnson sells a
'real' driver for it which supports any format up to 80 track double-sided.

					- Tim Koonce