[sebhc] H8 Emulator update

Dave Dunfield dave04a at dunfield.com
Wed Jun 2 07:54:08 CDT 2004

>>I need to understand how HDOS knows what size the drive is.
>>If you could give me bootable images for 40-track DS, 80-Track SS
>>and 80-track DS, what would help a lot.
>All the size info comes from the label sector.   But bootable?  Wouldn't 
>just mountable do?  I made up some blanks in various formats (by hand, I 
>don't actually have a ds, 96-tpi drive) and put them in a new empty-init 
>section under disk-images.   I haven't yet made my fantasy 512-track 
>megafloppy.  :-)
>But be aware these images aren't tested themselves.  Maybe Eric's sftool can 
>help confirm their integrity when it's uploaded.

Mounable should be OK - I requested bootable, because if I could boot it I
would be more confident that it's working correctly - I don't really have
much in applications to read/write in HDOS (I suppose I could write a BASIC

>>[I'll bet this is one reason why INIT doesn't work - I don't
>>  currently accept data for sector headers, and would therefore
>>  not return the right volume id after an init - I'll have to
>>  check into this]
>No, it never gets that far .. the message "Wrong type of media ...".
>indicates that initial media tests (involving index hole timing) didn't 

Could you give me all the gory details of exactly what it is looking for
an exactly how it is performing the timing ... ?

This is likely to be very tricky to emulate in the simulator.
Currently, the simulator is using a "trick" to allow the disk timing to
work for any virtual CPU speed (not counting the software delay loop in
HDOS 2.0) - that is it uses the I/O events to the disk port to adjust the
timing of the virtual disk rotation - it keeps in step with the software
driver's accesses in order to present the right thing at the right time
no matter how fast the VCPU is running - this is likely to break in the
init code if it is doing a separate timing of sector hole index pulses.

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.

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