Date   : Wed, 24 Nov 2010 09:38:57 +0000
From   : philb@... (Phil Blundell)
Subject: Harddisc fakery using a microcontroller

On Wed, 2010-11-24 at 16:16 +1100, paul aslin wrote:
> Couldn't this be implemented with a shift register/UART chip and some
> AM26LS series chips. The flux reversal part created using
> riseing/falling edge triggered gates.
> That would reduce the amount of work the AVR etc would have to do, and
> solve some of the timing issues.

Having thought about it a little bit more, I think probably the best way
to do this would be to have a cylinder-sized buffer in SRAM with some
dedicated logic, a CPLD or something, which would continuously scan
through the buffer, generating index pulses at the start of each pass,
and clock bits in or out (depending on state of WRITE_GATE) of the ST506
data interface.  The microcontroller would then be responsible for
saving and loading the contents of the cylinder buffer to/from the
backing store whenever a seek command was issued.

I don't think the software would be massively complicated if it was
implemented that way, and the hardware oughtn't to be very
difficult/expensive either.  Sounds rather easier than trying to do
everything in software on the microcontroller.

p.