[Coco] Nitros9 & Mess

[John Collyer]

----- Original Message ----- 
From: "Nathan Woods" <npwoods at cybercom.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Monday, February 02, 2004 10:57 AM
Subject: Re: [Coco] Nitros9 & Mess


> Bill Nobel wrote:
>
> >  So far I have found a couple of things that could be a possible bug.
> > There is no way the JVC drivers can function correctly with a virtual
> > disk that is NOT an exact size of the disk (even 256 byte boundry).
> > If it is out by 1 byte it will use the very fist byte as a sector size
> > and will scramble disks. if it is not of the same value for the
> > original drive.
>
> This is an interesting issue that has been somewhat confusing for a good
> amount of time.  MESS supports the JVC file format as described here:
>
>     http://home.netcom.com/~tlindner/JVC.html
>
> The problem is that the JVC file format is somewhat fragmented.  At
> first the file format was a simply a straight dump of 256 byte sectors.
> When Jeff introduced his CoCo 3 emulator, he added support for headers
> that could be used to specify the disk geometry.  The size of these
> headers are determined by examining the file size modulo 256.

First off there is no header information like what you described to
calculate.
The emulator checks the .dsk file and if it is not a multiple of 256 it gets
and
bleeds off the first byte of the .dsk file and saves it as sectors per
track. The
file pointer is now in the correct position inside the virtual file for
anymore file
I/O it does. There is nothing to calculate because there is no other header
information other than this.

> problem is that other tools such as PORT.EXE do not support these
> headers and will create disk images with lengths that are not modulo 256.

PORT.EXE does not create disk images. It uses ones that have been already
created.

> So the net result is that we have what are effectively different disk
> image formats and some tools and emulators will generate disk images
> that are incompatable with each other, and it isn't clear how these
> weird disk images should be handled.  When coding MESS, it was not my
> intention at all to fragment the JVC format, but it is unavoidable when
> there isn't a clear standard that all tools follow.

I think the confusion that your suffering from is your attemp to create some
kind of standard that was never used. I'm wondering why you just didn't
implement this standard as the standard you would use for your MESS
program.

John Collyer