11 Nov
2007
11 Nov
'07
11:37 p.m.
Subject: Re: Tarbell is making me insane
From: Grant Stockly <grant at stockly.com>
Date: Sun, 11 Nov 2007 13:21:32 -0900
To: "General Discussion: On-Topic Posts Only" <cctech at
classiccmp.org>
Tarbell Update
Ok you have 28k ram. Is the image sized and booting in that?
If the image is sized for say 32 or 48K it will crash, likely
as a bounce back to rom monitor.
>> > Also sounds like oneshot problems.
Check cpu timing. Even small timing
>> > errors tend to magnify bus noise issues and incompability problems.
>>(Snip)
>> > Also HEAT. That thing despite a very heafty noisy fan and cover mods
>> > didn't like heat. FYI: the timing of the oneshots drifts with heating!
I can't speak for the exact combination of the Tarbell, but the
system has been running all day long with:
-16k static card
-8k static card
-4k static card -2SIO
Is the boot image set up for MITS 2SIO and does it set it up?
-1k ROM
-8k Byte saver
I assume thse are in high memory and not below the address the image will
try to boot to. CP/M wants from 0000h to system size as configured.
When working on FDCs I load the system with a single known good RAM16,
Ram17 or similar 64k static card that can kill the last 4 or 8k. I use
a CPU with resident monitor and local ram (compupro CPU Z) and an
CPro Interfacer for IO. At that point I know I have a known IO,
known CPU and a monitor at F000h with POJ to F000h and ram at F800h.
Any time there is doubt about these they get a quick retest in a
known backplane (NS*Horizon). This means the system will be 4
boards max with the 4th being the FDC in question. I keep a CCS
terminator card handy as it seemed to work the best of all of them.
Things I've found in old backplanes.
Staples under the S100 connectors.
Metal under the backplane shorting to chassis.
Terminators with burned off tracks.
Metal bits in the connectors
Bits of nonconductor in the connectors.
Green cruft in the connectors (corrosion)
Black card edge connectors (gold over copper
without nickle flash, a bad thing)
Power supplies with excessive ripple. (tired caps)
Power traces fried on the backplane (altair 4slots)
Signal traces missing... from a former short?
That doesn't even touch on cards that just didn't play
well in some machines or with certain other cards.
Heres an example of a machine.
I have two explorer 8085s. One I built back when
and another aquired. They are identical as best as
I can see or test. Mine runs perfect, always did
with any card I've tried. the second is flaky,
won't run any S100 card without a bus terminator
and even then it's fussy. I've gone as far as to
completely swap every chip (they are fully socketed)
between the one that is cranky and my old one is
still happy and the newer one not. I've even swapped
PSs ( uses s100 style unregulated) and no dice. All
on board (there are a few) regulators replaced on the
bad one. No help. After a LONG time of testing and
all the problem was a high resistance trace on the
faulty board. I can see the signal at the source IC
solder side but between there and it's terminus it's
a 1000ohm resistor! One of the S100 status signals
was not quite there and floating. I bridged the
trace with blue wire between the two solder pads
and it's solid now. I cannot even with a 10x scope
see where the apparent crack is. That's chasing a
phantom.
But I do find the oddest of the odd.
-Tarbell FD
It has been running solid a 4K ROM monitor from Dave
Dunfield. Floppy interface still doesn't work on either card, and
these cards were tested by someone else on an IMSAI with an Altair CPU card.
If it's the monitor I think, it doesnt stress ram just sitting there.
You need a memory exerciser running at a minimum to be sure.
Some Z80 cards
complicate the issue. They have different timing and at 4mhz
some ram MAY NOT be fast enough. Either slow the z80 to 2mhz or more wait
states from ram.
The card I have has a switch for 2MHz. The tarbell with the reduced
clock speed will not work at anything higher like you suggested. I
have confirmed (from the person who shipped me the tarbell cards)
that the tarbell card with a reduced clock speed works normally with
a Z80 at 2MHz.
I attached a logic analyzer to the drive and watched all of the
signals. Every thing looks normal to me. I hooked it to a 5.25"
drive and then to a 3.5" drive. The drives are sending everything
that they should.
Then the FDC is potentialy not decoding the data.
Shows how rough the bus timing and noise can be.
Is that a one piece
backplane of the two sided variety or the one of the earlier Altair
4 slot chains or single sided backplane? The reason is the earlier
2x4 slot motherboards, but all of the wires are the same length
(there was a tip on that to reduce noise) I'm going to let the thing heat soak and then check
the bus with an
oscilloscope and the CPU clock.
if the oneshots are good ones once set they should say put. Then again
there was lore and fact about what was and wasn't good.
You know, I'm worried that the reliability issues
aren't related to
the Altair, but to a heavily modified tarbell card trying to write a
Tandon SSSD 5.25" onto a 3.5" disk???
Likely if the data rates are not set right for the FDC and it's data
seperator (usually also oneshots) is not set right it will fail.
Could even be a simple bad IDC crimp on the cable.
Would any of you like to see the data coming out of the disk
drive? I can upload the logic analyzer data to my web site...
Not I. If I did at the very least I'd also need to see the schematic and
jumper info for the tarbel. Other wise it's just a pretty picture.
I will never be happy until I find the problem.
I'd like to think
that with all of the information we have that I can make the Altair
as reliable as any other S-100 system. I have collected a lot of
errata and have applied it all to my system... That's why I won't
give up with this setup. : )
Most of the erata is lore not hard tried fixes. Most fall in the
"it worked for me" realm.
The problem is you have a lot of still possibles lurking.
Oh, SA400 drives... had a problem with them and all that used
that frame (sa400, 400l and 450). Seems if the spindle bearings
go bad the amount of jitter on the data can exceed that of simple
data seperators used with 1771 (especially RS early TRS80 with
early EI). I'm sure it's possible to have the same problem with
other drives. Showed up best with the SA alignment disk and
a dual trace scope set up for data read EYE pattern.
Allison
Thanks,
Grant
12 Nov
12 Nov
9:43 a.m.
Allison, thanks a lot for the detailed response! A lot of that info
can be used to help other people too!
I've written this e-mail from the "bottom up", so some things may
seem out of order in the time line.
I think that I'm to the point where I've narrowed the problem down to
inside the tarbell card, but I don't think the problem is the
1771. Any further hints are well appreciated. : )
I think we're getting closer!
Reading A Sector
ERROR: Record Not Found!
"
When I swap to the "better" tarbell, the basic sector read command
passes. (BTW, the reliably bad one above did boot CP/M once and gave
me a few good sectors!!! And I've swapped the 1771 between boards
and the bad stays bad and good stays good!) Basically I use the
monitor to clean the memory, load my program, and then I flip the
reset switch on the Altair. The Altair runs my program which starts
at 0000 and then jumps back into the rom monitor. Here is the
tarbell being good:
"
MON85 Version 1.1
Copyright 1979-2006 Dave Dunfield
All rights reserved.
> F0000 3000 00
> L
Reading A Sector
MON85 Version 1.1
Copyright 1979-2006 Dave Dunfield
All rights reserved.
>I can't speak for the exact combination of the
Tarbell, but the
>system has been running all day long with:
>-16k static card
>-8k static card
>-4k static card
The disks are 24k CP/M 1.4, the 4k is for the monitor. Forgot to say
that... Included on my source disk (which is read by the flaky
tarbell) is a BIOS for 48k CP/M, but I have never had it going long
enough to patch, movcpm, or whatever it is that has to be done to get
the new CP/M onto the disk...
Ok you have 28k ram. Is the image sized and booting in
that?
If the image is sized for say 32 or 48K it will crash, likely
as a bounce back to rom monitor.
See previous response for a description. When it runs, it
runs. When it doesn't...it doesn't : (
I spent all day long writing my own tarbell driver / monitor program
that would select, reset, seek, read, write, etc. When I tried the
read monitor command for the first time I didn't get an error. I
tried booting CP/M and it worked... Then I swapped to the more
troublesome tarbell card to get errors (I know, stupid) The problem
appears to be within the tarbell card. I can reliably get my tarbell
monitor to report this:
"
m2000
2000 1E 0A 31 00 01 21 00 45 16 33 0E
02 06 04 79 CD ..1..!.E.3....y.
2010 2A 00 15 CA 00 5A 06 00 0C 79 FE 13 DA 0F 00 3E *....Z...y.....>
2020 53 D3 F8 DB FC 0E 01 C3 0C 00 D3 FA CD 41 00 3E S............A.>
2030 88 B0 D3 F8 DB FC B7 F2 41 00 DB FB 77 23 C3 34 ........A...w#.4
2040 00 DB F8 E6 9D C8 1D C2 02 00 32 80 00 2F D3 FF ..........2../..
2050 C3 50 00 00 5A 80 04 19 00 02 00 45 80 04 15 01 .P..Z......E....
2060 01 80 51 00 00 00 00 00 00 00 00 00 00 00 00 00 ..Q.............
2070 00 00 00 00 00 00 00 00 00 00 00 00 00 C3 00 00 ................
"
I have to pull the card out to enable the boot rom...guess what, it
boots...but at the moment it is only reading "real" DD media. The HD
media with the tape "works" but BDOS complains about "bad
sectors". This HD disk on another day works just fine.
I ran one of the programs:
"A>disktest
TARBELL MINI-FLOPPY DIAGNOSTIC OF 8-1-80
STANDARD VERSION 1.8
40 TRACKS 18 SECTORS
SELECT DRIVE. (A/B/C/D) a
HOW MANY RETRYS? (0-9) 4
SELECT STEP RATE. (S=40MS,M=20MS,F=12MS) m
FULL TRACK SEEK? (Y/N) y
TO START TEST TYPE RETURN.
0 READ ERRORS DETECTED.
REPEAT TEST? (Y/N)
"
Maybe that gives you a clue as to what I'm working with.
And if I try my HD disks it does this: (to every sector on every track)
"
READ RECORD NOT FOUND ERROR.
TRACK 0 SECTOR 1
READ RECORD NOT FOUND ERROR.
TRACK 0 SECTOR 2
READ RECORD NOT FOUND ERROR.
TRACK 0 SECTOR 3
"
Last weekend that was my boot disk and I had several basic programs
compiled with basic-e on it.
Is the boot image set up for MITS 2SIO and does it set
it up?
I have a session captured from "once upon a time" when it booted
(which is more random than anything I can think of)
"TARBELL 24K CPM V1.4 OF 7-20-79
2SIO MINIFLOPPY VERSION.
HOW MANY DISKS? 2
A>dir
A: CPM COM
A: SYSGEN COM
A: DDT COM
A: COPY COM
A: PIP COM
A: ASM COM
A: STAT COM
A: ED COM
A: FORMAT COM
A: DISKTEST COM
A: DUMPDSK COM
A: BASIC COM
A: RUN COM
A>
"
I assume thse are in high memory and not below the
address the image will
try to boot to. CP/M wants from 0000h to system size as configured.
My bytesaver is at C000 and 4k of sram for the monitor is at
E000. There is 24k of contigous memory at 0000.
Doesnt assure the FDC is set right for the drive and
media.
Also doesnt assure the media is SD or even bootable.
Further is the media is not using a 2sio as the IO the system could
boot and crash or appear to.
The drive, tarbell, and boot disks were mailed to me from a fellow
enthusiast. He made all of the modifications, made the disks,
etc. He has tested the setup in an IMSAI (kind of) with my (kit)
CPU, a SSM 8080, and a ZPU at 2MHz.
To add to that, I have myself booted off the setup, formatted disks,
made copies, ran the basic compilier, ran asm, etc. But something
(and I think its IN??? the tarbell card does not like me, Alaska, my
Altiar... I don't know! : (
A quote:
"My Imsai has a standard front panel with a factory suggested mod. to
do a power-on halt at zero. It has two 16K Industrial Microsystems
static ram boards, a SIO2 serial board and a SSM 8080 CPU. The prom
on the Tarbell is turned off to let the front panel operate properly
at power on. The Tarbell is then booted by using a MITS eprom board
and the 1702A eprom you burned for me. The power supply is a
Industrial Microsystems switching supply which powers both the drives
and the backplane
Following is the different configurations I have used in the test
unit to boot the Tarbell;
1. With a Z80 Cromemco ZPU set at 2Mhz, power-on jump set to
zero and no front panel. The Tarbell boots at power-on and will do a
cold boot every time
you push the reset button.
2. With a ZPU and Imsai front panel the Tarbell boots
only when the run switch is pushed.
3. With the Altair CPU and no front panel the Tarbell will not
boot at power on or after a reset!
4. With the Altair CPU and the Imsai front panel the Tarbell
will boot after you push reset and then push the run switch.
After the Tarbell boards boot I have never had a problem or dropout
in CP/M with any CPU- front panel configuration. The static ram
boards use low power chips and run cool.
Remember my Altair CPU board uses a 8224 in the oscillator circuit
and I replaced the 8T97 with 74LS367's.
"
This is some info on the mod:
"The modification we have on our Tarbell boards was designed for the
5.25 Tandon TM-100 single sided. single density 48tpi drive which was
one of the first 5.25 drives produced. It might be that some of the
new 3.5 drives just won't work with the setup we are using."
Could even be a simple bad IDC crimp on the cable.
I have tried a few FDC cables. Maybe I should make a new one.
Time for bed. : (
Grant
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ajp166＠bellatlantic.net -
grant＠stockly.com