Tandy 600 Programmer's Reference Manual page 125

Descriptions of
Device
Driver
Entry Points
The following entry points must be provided
in
a device
driver
file;
DVCTRL
-
Device
Driver
Control
This entry point
is
used
for
controlling
the device
driver
file
during
installation
and
removal.
This entry point
will
be
called with a
FAR
call.
When
initialization
is
complete,
it
should
return
with
a
FAR
return.
The
following functions are
required:
Function
-
Initialize
device
driver.
INPUT:
AH
-
Function
Code
OUTPUT:
none
ERRORS:
CY
set
if
error
occured.
BIOS
error
code
in
AL
This function
is
called
when
the device
driver
is first
installed to initialize
and
activate the
driver.
At the time
that this
function
is
called,
all
memory
has been
allocated,
and the driver
located at the correct
address
for
execution.
If
the carry
flag
is
set
on
return
from
function
call 0,
it
is
assumed
that
the
initialization failed
and
the driver
installation
will
be
aborted.
Function
1 -
Prepare
driver for
movement
INPUT:
AH
-
Function
code
DX
-
Address
driver will
be
moved
to
OUTPUT: none
ERRORS:
none
(must succeed)
When
the
HH
O/S
finds
it
necessary
to
move
a
device
driver, this
function
will
be executed
to
inform the driver of the
fact.
The
device
driver
must place
itself in
a
state
so that
it
is
safe
for
the
code
to
be
moved
to
a
new
location.
Function
2
-
Driver
Movement
Complete
INPUT:
AH
-
Function
code
OUTPUT:
none
ERRORS:
none (must succeed)
When
the
HH
O/S
has completed moving
a device
driver
file,
this
function
will
be
called
to
tell
the driver to reactivate
itself.
The
driver
will
be
at
its
new
location
when
this call
is
made.
Function 3
-
Deactivate Device Driver
INPUT:
AH
-
Function
code
OUTPUT:
none
ERRORS:
none
(must succeed)
When
the
HH
O/S
is
removing a
device driver, this
function
will
be
called to
tell
the
device
driver to
deactivate
itself.
Following the return
from
this
function,
it
is
assumed
that
the
system
is in
a safe state
for
the
device
driver to
be
removed and
the
original
BIOS
driver restored.
120