[sebhc] HDOS 2 boot problem identified.

Jack Rubin jack.rubin at ameritech.net
Tue May 25 09:30:23 CDT 2004

Dave said:

> I have identified the problem - the HDOS 2 driver in high 
> memory uses a software timeout based on the CPU speed while 
> looking for sector holes - on a moderately fast PC, this loop 
> breaks, and times out before sector holes are found. If you 
> hit F9 while the boot is hung, you can step through the code 
> and see where it is using BC as a timer while looking for the 
> hold detect bit.

This reminds me of another question I wanted to ask you earlier - I
think when you first started the emulator you had a problem with the
system looping off the top of the 8080 64K address space and coming back
into the ROM at 0. Didn't you add a "control" to prevent that?

By fixing that I think you've created a new device - an 8080 machine
with 64K of ROM/RAM and the ability to run HDOS 1.6. I don't have the
right combination of RAM cards and disks to test that in the real world
right now, but my 1.6 system stopped booting when I took RAM to the top
of the address space, though 2.0 runs fine in the same configuration.
IIRC, 2.0 changed the test algorithm used by 1.6 to locate the top of
memory before relocating itself to avoid this problem.


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