Intel 8272 based floppy controller & Missing Address Mark

[dkgrizzly at thewaffleiron.net]

Hi friends,

In the continuing saga of building a CP/M system with Pro-Log cards housed
in a Heathkit dual 8” floppy drive cabinet


I recently acquired a Pro-Log 7387 floppy disk controller card w/ manuals.
The 8272 chip on the card was fried (either before I got it, or by me doing
something stupid early on once I had acquired it), and so I replaced the
chip with another pulled from a 8-bit ISA floppy controller.  Now I am
getting some more reasonable replies out of the card.

Now I'm stuck with "Missing Address Mark" errors, no matter if I'm using a
real 8" floppy drive (8MHz FDC clock, appropriate settings in all the
software) or a GoTek floppy emulator (4MHz FDC clock, 720KB settings on the
GoTek & Floppy Disk Utility).
I can see the read data & read window lines working as I'd expect, so I'm
fairly confident that the read data separator and related logic is OK (I
even replaced the 74ls74 read data separator with no effect).
What am I missing that would cause a 8272 to always return Missing Address
Mark?

I'm using RomWBW, with the included FDU utility patched to talk to the FDC
at the correct addresses, and from the traces I've captured it appears that
side of things is working correct. I'm hoping someone out there has
experience troubleshooting floppy controllers and can give me some pointers.

-David


------ Trace with GoTek running FlashFloppy and emulating a 720KB drive
follows -------

RetroBrew HBIOS v2.9.1-pre.5, 2019-11-23

PROLOG Z80 @ 3.686MHz
0 MEM W/S, 1 I/O W/S, INT MODE 1
512KB ROM, 2048KB RAM

SIO0: IO=0xF5 SIO MODE=9600,8,N,1
SIO1: IO=0xF7 SIO MODE=9600,8,N,1
MD: UNITS=2 ROMDISK=384KB RAMDISK=1920KB
FD: IO=0xC4 UNITS=2

Unit        Device      Type              Capacity/Mode
----------  ----------  ----------------  --------------------
Disk 0      MD1:        RAM Disk          1920KB,LBA
Disk 1      MD0:        ROM Disk          384KB,LBA
Disk 2      FD0:        Floppy Disk       3.5",DS/DD,CHS
Disk 3      FD1:        Floppy Disk       3.5",DS/DD,CHS
Serial 0    SIO0:       RS-232            9600,8,N,1
Serial 1    SIO1:       RS-232            9600,8,N,1

PROLOG Z80 Boot Loader

Boot: (C)PM, (Z)System, (M)onitor,
      (L)ist disks, or Disk Unit # ===> BOOT CPM FROM ROM


CBIOS v2.9.1-pre.5 [WBW]

Formatting RAMDISK...

Configuring Drives...

   A:=MD1:0
   B:=MD0:0
   C:=FD0:0
   D:=FD1:0

   3623 Disk Buffer Bytes Free

CP/M-80 v2.2, 54.0K TPA

B> FDU

Floppy Disk Utility (FDU) v5.2, 08-Jan-2018 [HBIOS]
Copyright (C) 2017, Wayne Warthen, GNU GPL v3

SELECT FLOPPY DISK CONTROLLER:
  (0) Exit
  (1) Disk IO ECB Board
  (2) Disk IO 3 ECB Board
  (3) Zeta SBC Onboard FDC
  (4) Zeta 2 SBC Onboard FDC
  (5) Dual IDE ECB Board
  (6) N8 Onboard FDC
  (7) RC2014 SMC (SMB)
  (8) ProLog 7387
=== OPTION ===> PL

===== PL ==============<< FDU MAIN MENU >>======================
(S)ETUP: UNIT=00  MEDIA=720KB    MODE=POLL        TRACE=00
----------------------------------------------------------------
(R)EAD          (W)RITE         (F)ORMAT        (V)ERIFY
(I)NIT BUFFER   (D)UMP BUFFER   FDC (C)MDS      E(X)IT
=== OPTION ===> FORMAT (T)RACK, (D)ISK ===> DISK
ENTER INTERLEAVE [01-09] (02):



RESET DRIVE...
PROGRESS: TRACK=4F HEAD=01 SECTOR=01

===== PL ==============<< FDU MAIN MENU >>======================
(S)ETUP: UNIT=00  MEDIA=720KB    MODE=POLL        TRACE=00
----------------------------------------------------------------
(R)EAD          (W)RITE         (F)ORMAT        (V)ERIFY
(I)NIT BUFFER   (D)UMP BUFFER   FDC (C)MDS      E(X)IT
=== OPTION ===> READ (S)ECTOR, (T)RACK, (D)ISK, (R)ANDOM ===> TRACK
ENTER TRACK [00-4F] (00):
ENTER HEAD [00-01] (00):


PROGRESS: TRACK=00 HEAD=00 SECTOR=01
READ: 46 00 00 00 01 02 09 2A FF --> 40 01 00 00 00 01 02 [MISSING ADDRESS
MARK]
CONTINUE? (A)BORT, (R)ETRY, (I)GNORE ===>