14 Apr
2014
14 Apr
'14
5:17 a.m.
On 4/14/14, Seth Morabito <lists at loomcom.com> wrote:
Andrew Warkentin <andreww591 at gmail.com> writes:
Actually, Unix and the bootloader both write the correct values into
the SDH register (however, the ROM might not; it won't boot the hard
disk directly in the current version of the emulator - I'm booting
I have at last gotten Unix to boot to multi-user
mode in FreeBee (Philip
Pemberton's 3B1/UNIX PC emulator).
Magnificent! This is excellent news. Since I've been diving deep into
3B1 stuff recently, I've been hoping that someone was working on the
emulator. I'm glad to know it's active.
Actually, since we're on the subject, I hope you won't mind if I pick
your brain about something 3B1 related...
This weekend I started working on a small daughterboard to replace the
socketed WD1010 and act as a hard drive emulator, somewhat similar to
the FreHD TRS-80 Hard Drive Emulator[1], but piggybacking on the
motherboard instead of sitting in a bus expansion slot.
Tonight, I realized that part of my understanding was wrong. I believed
that Drive Number and Head Number were selected by writing to the SDH
task file register of the WD1010 -- in fact, they CAN be, but I fear
that the 3B1 doesn't do it that way. The hardware reference manual
discusses the Disk Control Register (a 74LS373 seen in the schematics on
page 11/D4), which is directly addressed through location 4E0000, rather
than through the SDH task file register at E0000C. It handles generating
the ST-506 Disk Select and Head Select signals directly.
In fact, the Logic Board Test Procedures in the reference manual make it
clear that the SDH register is loaded from the disk's ID field after
performing a reset and a SEEK command. None of the procedures show
writing to the SDH register, only reading from it.
So, if my understanding is correct, simply replacing the WD1010 is not
enough to properly emulate a disk system, unless I'm pretending to be a
single disk with 1 head. Aiee!
IS my understanding correct? Do you (or anyone else) have any thoughts
on this?
(Copied to the list, in case anyone else is interested)
-Seth
[1] http://www.vecoven.com/trs80/trs80.html
from a floppy with no kernel). The WD2010 emulation
that I contributed
a while back just uses the value written to the SDH register.
On 4/14/14, Philip Pemberton <classiccmp at philpem.me.uk> wrote:
On 13/04/14 08:38, Andrew Warkentin wrote:
You're welcome.
I already implemented the RTC a while ago, but my RTC implementation
was in an older copy of the source that I hadn't looked at for a
while. I forgot that I actually had it in a state where it mostly
worked (reading the date works, but attempts to set it are ignored).
Unix does have some Y2K issues though. I'll include the RTC in my
patches of course.
I did add a mapping of Alt+Return to Enter, and I found out that the
system sometimes still doesn't boot all the way. After I get through
the initial dialogs on boot, the system hangs after the "The screen is
being set up..." message. I just tried it now and instead of a hang I
got some messages relating to the modem, which I dismissed, and got to
a login prompt (I was able to log in and get a desktop), so I think at
least a stub of the serial controller will have to be implemented to
get it to boot reliably (I tried booting again and it just hung after
that message again).
Also, like I said before, the hard disk won't boot directly at the
moment; a floppy with a bootloader but no kernel (the install root
floppy works) is currently required. I think it might have to do with
the head select bits. IIRC you had implemented the Disk Control
Register properly in the new branch, and I'm using the OldMMU branch.
However, the emulator is still not quite usable.
The key mapping is not
quite right (one problem is that the UNIX PC has separate "return" and
"enter" keys, and there is no mapping for "enter", which is required
to
accept dialogs, and there might be other important keys that are
missing). Also, neither the mouse nor the RTC are emulated yet.
Andrew, all I have to say is "THANK YOU, THANK YOU, A MILLION TIMES -
THANK YOU!" The bus error logic has been a thorn in my side for ages,
and I just couldn't figure out what was going wrong. I'm really glad
someone managed to figure it out!
Get these patches to me and I'll merge them in ASAP and do my best to
fix the mouse, RTC and keyboard.
As you said, the main problem is that we don't have enough keys on a PC
keyboard to do a 1:1 mapping -- thankfully SDL supports Modifier keys,
so this isn't an insurmountable problem. The big problem is coming up
with a sane mapping :)
Truth be told, I'll probably move the repository over to Bitbucket so
people can fork it and work on it independently, then submit merge
requests. It takes a lot of work out of manually importing patches.
Is this based on the OldMMU branch or my revised MMU? I don't really
care which it is, I'll just deprecate the branch you aren't using so we
don't have a million and one build variants 8^)