On 25 Nov 2006 at 13:29, Dave Dunfield wrote:
Well - then I guess NorthStar was obscene... :-)
My comment was directed toward your reference to the Tarbell
controller, not the NS.
I didn't mention the Tarbell - I was going by the subject line.
The
single-density controller does indeed have 256 byte of ROM (in three chips!)
The double-density one has 512 bytes of ROM.
A question crops up: why? What's the point--you need only enough to
load a sngle sector. Was the NS controller so badly implemented
that it required that much code to read a single sector?
It's a complete hardware (no chip) floppy controller - knowing how it works,
I think you would be very hard pressed to successfully home the head and
read a sector in 32 bytes.
In 256 bytes, they implemented that, and part of the OS disk driver - it's
kinda weird how they did it, the OS call links back to the disk ROM, which
in turn links back to the OS code for the write/verify functions they didn't
have in the ROM - when I did my DMF OS for the NorthStar, I had to
completely abandon their ROM because of the fixed references to locations
in the 2000+ block where the N* OS loads (mine loaded at F000 up above
the disk controller leaving the rest of RAM free.
I have a commented disassembly of the SD ROM up on my site in case
anyone is *really* interested.
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools:
www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html