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Blocking and Deblocking
1-2
The SELDSK entry point clears the host buffer flag whenever a new disk is logged
in. Note that although the SELDSK entry point computes and returns the Disk
Parameter Header address, it does not physically select the host disk at this point (it
is selected later at READHST or WRITEHST). Further, SETTRK, SETSEC, and
SETDMA simply store the values, but do not take any other action at this point.
SECTRAN performs-a trivial function of returning the physical sector number.
The principal entry points are READ and WRITE. These subroutines take the place
of your previous READ and WRITE operations.
For hard disk, the READ and WRITE operations actually move data from or to a
work buffer. The work buffer is located on the hard disk adapter board starting at
location
9CaaaH.
This buffer is used by the CBIOS only and is not accessible to the
user for either programs or data.
The actual physical read or write takes place at either WRITEHST or READHST,
where all values have been prepared: hstdsk is the host disk number, hsttrk is the host
track number, and hstsec is the host sector number (which may require translation
to a physical sector number). You must insert code at this point which performs the
full host sector read into, or write out of, the buffer at hstbuj of length hstsiz. All
other mapping functions are performed by the algorithms.
See the listing of the CBIOS on the CP /M-86 Program Development Aids diskette
for the sector blocking/deblocking algorithm for the APC.
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