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CHAPTER 26
26.
INPUT/OUTPUT PROVISIONS
FOR
NON-SUPPORTED DEVICES
It
is
assumed
that
the
reader
is
device independent I/O functions
desc~ibed
berore this chapter is read.
familiar with
in
section
the
25.3
This
chapter
describes how the
I/O
functions interrace
with the
hardware
device
and
how
a
user
can
interrace
non-standard
devices
rO~
use with the device independent I/O
f
unc:
t
ions.
26.1
Device Dependent
IIO
The device dependent
liD
functions described
in
Chapter
2S
ror
accessing the console and the line printer cannot be
changed to access non-standard devices.
These routines are a
part
Or
MDOS and its basic environment requirements;
howeverJ
a
user can construct his own device drivers that are accessed
by
his
programs.
If
the
standard
MDOS
commands
are to
u~ilize
non-standard devicesJ
the user should be using
MOODS
(OEM
MDOS)
which
can be configured to work in that manner.
The COpy command (Chapter 7)
is
an exception.
It can load
a
user-defined
device
driver
into memory to copy
a
file
rrom
that device to the diskette or
fr~m
the
diskette
to
that
device.
26.2 Device Independent I/O
This
section
describes
how the device independent I/O
functions interface to the device
driv~rs
which,
in
turn,
interface
directly to the hardware device.
This description
applies to both standard and non-standard devices.
26. 2. 1
Contra
11
er Descr i p tor Bloc
k -- CDa
The Controller Descriptor 13lock,
OT'
CDB,
is a table that
describes a physical device and the types of input and output
operations that can be performed by the device.
Unlike
the
IOCB,
the CDB is configured only once ror each device.
It is
the memory location of the CDa that replaces the contents
Or
the
IOCGDW
entry
of
an IOCB after the. RESRV function has
been called.
The
format of the CDa is shown in the following
diagram.
Page
26-01
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