[Coco] CoCo SDC weirdness

David Ladd davidwladd at gmail.com
Fri Mar 3 22:01:12 EST 2017

On Wed, Mar 1, 2017 at 1:47 PM, Tim Fadden <t.fadden at cox.net> wrote:

> Don't get me wrong, this is not a complaint, I love me sdc cards.
> I have been having the following symptoms/features?
> I have two scsi drives attached, and use the floppy do boot into nitros9,
> and the scisi is the /dd device.
> This works, and I can use the floppies, SDC, and drivewire.
> So I was thinking it would be nice to be able to boot off of the sdc card
> the same way.
> I took a 40tk nitros9 dsk image and used deldir to clean off the files.
> Then I used the custom build script/bootlists minus the format sdc doesn't
> like that. :-)
> Ok, the sdc dsk image gets created with no problem, and I am able to boot
> from it.
> It changes over to the /dd (scsi partition) I can access the scsi, sdc and
> drivewire.  But when trying
> to access the floppies it accesses the sdc instead.  taking a look at the
> device descriptors of
> /do and /sd0 everything looks correct.

​This is because you probably had the MPI switch set to the slot with the
CoCoSDC rather than the slot with the real FDC.

The floppy disk drivers in OS-9 or NitrOS-9 are not aware of the slot the
real FDC is in.  Since the CoCoSDC also emulates being a FDC that is why it
responds to the FDC commands given by the floppy drivers.

This is also why on all my CoCo setups I have always had my RGBDOS, HDBDOS,
or other custom Disk Basic ROMs always in the FDC as to make sure I don't
run into these issues.

I know for a lot of people this can also be a draw back to this.

It has been brought up before with accessing the real FDC via a POKE from a
AUTOEXEC.BAS program on your default RGBDOS/HDBDOS drive.  As far as
default startup on CoCoSDC you will just have to manually enter the POKE or
store a basic program on a disk image that does the POKE for you and call
it every time you start up the system.

Maybe if someone gets around to reproducing floppy controllers they could
make a version that has flash chips so custom ROM's could be as easily
updated on the FDC as it is on the CoCoSDC. :D

> ​<cut>
| David Ladd a.k.a. PacoOtaktay a.k.a. Drencor                          |
| YouTube: http://www.youtube.com/user/PacoOtaktay                      |
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| Do you have your CoCo 3 yet?                                          |


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