From: uhclemLOSE.jun08@nemesis.lonestar.org
Knut Roll-Lund wrote:
: The extra ROM is in the unused area between the level 2 ROM and the
: memory mapped keyboard (i/o). The model III/4 extra ROM contains code
: for higspeed cassette ("1500 baud") some keyboard driver stuff and
: RS-232 drivers (anyone know? is there a way to enable/use those from
: basic?).
"Anyone know" what? You mean, what items are in the "C" ROM?
It's primary function is to house items that are likely to be
hardware model independent, so the cheapest ROM would hopefully be
the only one needing replacement. So frequently the difference between
the US and French or other keyboard models would be only a different
"C" ROM. It didn't always work out that way, but that was the goal.
Most of the entry points for Model III mode (quite a few are in the
"C" ROM or are RAM vectors that point back to the "C" ROM) are
documented in the Model III Hard Disk System documentation, and an
unofficial list is in the LDOS 5.1.x manual set. The RAM hooks also
allowed you to replace the ROM version of a driver with a RAM-based
one, or at least get your hands on requests before passing them on
to the ROM code.
The Model III/4/4D "C"* ROM region is 0x3000 to 0x37FF (2,048 bytes)
contains the following:
* This is included in the larger "D" ROM on gate-array Model 4/4D systems
that absorbed the "B" and "C" ROMs, plus 2K that could be used as
an alternate "C" ROM region, mapped also at 0x3000 to 0x37FF.
1. Entry point table (mainly "C" ROM documented entry points)
2. Hardware initialization, like floppy, interrupt, clock, display (all)
3. Low RAM initialization values, including vectors back into ROM (all)
4. Floppy boot (all)
5. 500 and 1500 baud cassette routines, including "Cass" prompt code,
even though the string itself is in the "A" ROM.
6. Keyboard driver (US, French, German, KANA, others)
7. Network III boot (some educational versions)
8. Network 4 boot (some educational versions)
9. Clock/Time-of-day routines (there were 50Hz and 60Hz versions)
10. RST 38 Interrupt poll routines (all)
11. RS232 driver with initialization, input and output routines (all)
12. KANA Keyboard hooks (most US versions)
13. Daisywheel-II kludge fix-up routine (apparently all)
14. Screen print support (all)
Despite having entry vectors, some routines and even some points
within some routines within the "C"/"D" ROM have to be in exact places
because popular programs were jumping into the middle of things
rather than using the provided vectors, and in a few spots the
one ROM does the same sort of direct reference into one another ROM.
So some of the internal layout is twisted around these requirements.
The XROM/XDROM replacement version re-wrote many of the routines
in the "C" ROM, except for some sections with specific timing
or placement requirements. The original goal was to get more space and
it was enough to have Network III and Network 4 boot, floppy boot
and a hard disk boot (Tandy, Powersoft, or Misosys SCSI) all present
at the same time. (Most of the space came from writing a much
more efficient keyboard driver.) XDROM also included Memory, Video
and Floppy diagnostics accessible via a motherboard option jumper.
Both XROM and XDROM also had room to fix a number of long-standing
bugs or limitations and improved quite a few things, most of which
are only visible when run in Model III mode.
Note also that the Model I naming of ROMs varied by Level I or
Level II, and both were different than the "A" (8K), "B" (4K) and
"C" (2K) of the Model III/4 and the "A" (8K) and "D" (8K) of the
gate-array model 4/4D.
Frank Durda IV - send mail to this address and remove the "LOSE":
http://nemesis.lonestar.org
"I'll huff, and I'll puff, and I'll get promoted." - Old Tandy
management saying.
Copyright 2008, ask before reprinting.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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