Tarbell is making me insane

Grant Stockly grant at stockly.com
Mon Nov 12 03:43:21 CST 2007


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!

> >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:

"
 >

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.

 > 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 



More information about the cctalk mailing list