CPQPATCH v1.0                                    12 August 2008, John Elliott
=============================================================================

  CPQPATCH patches the BIOS ROM of a Compaq Portable so that it can boot from 
a hard drive whose own ROM doesn't support booting an XT.

  To explain a little:

- On the original PC and XT, the BIOS ROM doesn't know anything about hard 
drives. The hard drive controller comes with its own ROM, and this handles all 
aspects of the drives, including booting from them.

- On AT-class machines, the BIOS ROM does know about hard drives, and supports 
ATA drives itself. Additional hard drive controllers (eg: SCSI) can get away 
with just adding the drives to the system; the BIOS handles booting.

  So, I had a Compaq portable, and an add-on drive for it (2Mb of flash on an 
ISA card) which left booting up to the BIOS. The attached program will patch 
the revision C ROM so that it will boot from my add-on drive. It should also 
work with the Future Domain TMC-850 (firmware 8.4 or 8.5).

  The C source (cpqpatch.c) includes the assembly language source code for
the changes made.

To use CPQPATCH:
~~~~~~~~~~~~~~~~

You will need:
* A Compaq Portable
* An EPROM burner
* A 2764 EPROM, 28c64 EEPROM, or compatible chip.

1. Get hold of a Compaq Portable BIOS image (revision C). This should be an 8k 
file. If you have a Portable, you can check the BIOS revision with DEBUG:

A>DEBUG

-DFFFE:6,f
FFFE:0006  43 20 20 20 43 4F 4D 50 51 51                       C   COMPAQ
-

  The 'C' by itself is the revision number.

  Either save the ROM with DEBUG, or image it once you've dismantled the PC.

2. Take the motherboard out of the Portable.

3. Remove the BIOS ROM. This should be marked 100666-1 (or 1006661) and be 
  plugged into a socket near the DIP switches. If you haven't imaged it, do so 
  now.

4. Run CPQPATCH:

     CPQPATCH bios.bin new.bin

  where "bios.bin" is the original BIOS, and "new.bin" is the name you want to
  give to the patched version.

5. Burn "new.bin" to an EPROM or EEPROM.

6. Put that EPROM/EEPROM in the socket where the BIOS ROM came from. The 
  silkscreening on the board should show you which way round it goes, but in 
  case it doesn't, the end with the notch should point in the direction of the 
  ISA slots.

7. Put the whole thing back together, power it up, and hope it works.