RQDX3 formatter

[Charles Dickman]

On Fri, Aug 3, 2018 at 10:22 AM, Christian Corti via cctalk
<cctalk at classiccmp.org> wrote:
> Where do you patch the ZRQCH0 binary to use different geometries for non-DEC
> drives with a RQDX3?
> As it seems it should be possible, but noone has told how to do this ;-)
>
> Christian

You patch the disk description table in the formatter (ZRQC) that gets
downloaded to the RQDX3 during formatting.

The table has about 30 parameters in it and needs to be consistent.
Unfortunately it is not as simple as just supplying geometry, it is
also necessary to determine how to allocate diagnostic and bad block
areas of the disk. There is source for an early version of ZRQC on
bitsavers ( http://www.bitsavers.org/pdf/dec/pdp11/microfiche/ftp.j-hoppe.de/bw/gh/AH-U110C-MC__RD31-51-52-53-54,RQDX3,RX33__RQDX3_FORMATTER__CZRQCC0__(C)1985-86.pdf
) and this has the format of the table and the contents for some of
the standard DEC disks (RD51, RD52, etc). The version that has source
available is not in the normally available XXDP images, so once you
know what the table looks like, you have to find it in the version of
ZRQC that you have and patch the binary.

The later version of ZRQC has more disks in the table. The one that I
used had RD51, 2 types of RD52, 2 types of RD53, RD54, RD31, RD32, and
RD33. I took the contents of the table and the additional entries to
try to figure out how to allocate regions when the disk got bigger.
Interesting too is that the source on bitsaver's has a conversational
mode that would let you enter the disk tables by answering a series of
prompts. This was not in the version that I had on disk.

The spreadsheet link on this page:
http://www.chdickman.com/pdp11/RQDX3/ has my calculations. Sheet1 is
probably useless to anyone. Sheet 2 has the tables for the various
disks and the calculations I used to try to determine what size to use
for new disks. sheet 3 has the new disk calculator on it. In the
Custom column, the blue cells are inputs, the orange values are
calculated and the black values are "standard".  The HEX and Octal
columns were to help when filling in the XXDP table. USE AT YOUR OWN
RISK.

-chuck