[Coco] [CoCo] bootlink, SH, NitrOS-9 info needed

[Gene Heskett]

On Friday 08 September 2017 00:11:41 David Ladd wrote:

> Gene Heskett,
>
> I am asking this if you still remember off hand or anyone else whom
> has used the /SH descriptor for accessing the HDBDOS vdisk #'s from
> within NitrOS-9.
>
> I was reading your documentation Gene for bootlink and see that using
> this SH descriptor for what ever superdrive HDD interface you are
> using you can access your virtual HDBDOS drive's.  What I would like
> to know is where does one find this SH driver or build it?
>
> I have been browsing the NitrOS-9 repo looking for a reference to this
> SH descriptor and didn't see one other than listed in your
> documentation. Just wanted to know if this is still a valid option in
> current NitrOS-9 and RBSuper or no?
>
> Thanks :D
>
Sure is, or was the last time I pulled and built nitros9. About 18 months 
back now.

Let me see if I can describe the requirements to use it. Starting with 
the superdesc.asm, you'll need to set the descriptor option that splits 
the 512 byte sector into a low half and high half of 256 bytes each, so 
that you can make use of every byte of the 512 byte disk sector.

This, when a disk read is done, hands os9 the low half of the sector if 
the sector address is an even number, and the high half of the sector if 
the address is odd.

Next, get the hard drives lsn0, first 3 bytes, which is the hex 
representation of the size of the portion of the disk which is allocated 
to os9's use. Call it a partition if you'd like because thats what it 
is.

Add 1 to that hex value and break it into 2 pieces to be written to the 
sh descriptors ofs and wpc positions in the descriptor. What you just 
did was to give that descriptor the starting address of the first byte 
of the first 35 track floppy image, in the first bank of 256 disk images 
usable by hdb-dos and basic. There's another bit in the /sh descriptor 
that enables the "stp" value to set the disk images offset so that all 
256 disk image locations can be used from one descriptor, just change 
the stp with dmode and you are looking at a new disk image. This won't 
work for hd to hd copies, you'll need two descriptors for that since the 
stp does not take effect until os9 has had a chance to reread lsn0 and 
update its drive tables. That never gets a chance to be done while doing 
a copy.

This scheme can be repeated by setting up an additional descriptor and 
adding 35*18*256 to the value placed in /sh for the initial 3 byte 
sector offset to establish the start of the 2nd bank in /si, step & 
repeat for /sj, /sk etc until the hard drive has been fully allocated.

There are several other ways to make use of the basic /sh skeleton, I 
have even, before I had drivewire working, located where I had put an 
install .dsk image on the hard drive using a serial cable and rzsz, took 
its address from the file descriptor, and pointed /sh at the image, and 
actually installed it from where that file was sitting just as if it was 
a floppy image, except it was much faster since it was being accessed at 
the hard drives speed.

One huge, HUGE caveat! Once you have first of all these descriptors 
configured, make a new directory someplace safe (marked real floppy?) 
and save all those descriptors as you get them figured out, because all 
this data is going to be unique to your system.  And recovering it if 
its lost is going to be a 9 digit excedrin headache.

This means you will need to write a script so that anytime you make a new 
build, you can copy all those descriptors back over the top of the ones 
just built else you will be reinventing several different sized wheels 
before you are up and running on the new install. I usually do that 
while the install image is mounted by drivewire.

And I've no doubt left out some vital details, so use superdesc.asm as 
the final word. Unfortunately its too terse and concise and will need 
several reads.  Or it sure did for me. But as I come up on 83 next 
month, I find myself pleading oldtimers way too often. :)

It can be complex until the lights come on but don't give up.

Cheers David, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>