Date   : Sat, 11 Apr 2009 20:22:54 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: ADFS 1.53 patch

Jason Flynn G7OCD wrote:
> Does anyone know if this supports both 8bit and 16bit transfers
> type IDE interfaces?
 
It supports 8-bit and 16-bit /interface/, ADFS is an 8-bit filing
system and so just transfers the low byte of each 16-bit data word,
so it's irrelavant whether you use an 8-bit interface (with no
access to b8-b15) or a 16-bit interface (where b8-b15 are ignored).
 
ADFS does not and cannot do 16-bit /transfers/. ADFS is an 8-bit
filing system, it stores 256 bytes in each sector. You can't just
stop transfering data halfway through a 512-byte sector or start
transfering data halfway through. To use all 512 bytes (256 16-bit
words) in an IDE sector you'd have to load all 512 bytes into a
buffer, modify the 256 bytes you want to modify and then write all
512 bytes back out again.
 
ADFS can only access a maximum of 512M. Throwing away hald the
storage capacity of a 2G IDE drive doesn't make any difference, as
ADFS can only see two paritions of 512M anyway.
 
How is the documentation at http://mdfs.net/Info/Comp/BBC/IDE not clear
on this?
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
In 1939 $50 of groceries would fill three station wagons. Today I
can lift $50 of groceries with one hand. I must have got stronger.