UNSPOOL.ASM			81-11-12
for CP/M 2.0 and up.

AUTHOR:			Gary P. Novosielski

INTRODUCTION:

	UNSPOOL (Ver 2.3) is a program to send a standard
CP/M file such as a .PRN or .ASM file to the system's list
or punch device, while still allowing other system operations
to take place.  The file is transferred during periods when
console is waiting for input.

SYNTAX:

	UNSPOOL [d:]filename.ext [dev]
	[square brackets denote optional parameters]

	Where	d:		is an optional drive spec
				such as A: or B:.  If not
				entered, the current default
				drive is assumed.

		filename.ext	is the name of the CP.M file
				to be printed/punched

		dev		is the symbolic name of the
				output device to be used.
				Valid devices are LST and
				PUN.  Note that the colon (:)
				usually present in these names
				is NOT entered.  If not
				specified, the LST: device is
				assumed.
Examples:
	UNSPOOL TEST.PRN
		will send the file TEST.PRN from the current
default drive to the current LST: device.

	UNSPOOL A:TEST.PRN LST
		is exactly equivalent to the above, assuming
drive A is the default drive.  Note that the device name has no
trailing colon.

	UNSPOOL B:ZINGER.HEX PUN
		will send the file ZINGER.HEX from the B drive
to the current PUN: device regardless of which drive is
currently the default.  Note that the device is "PUN"
not "PUN:".

OPERATION:

	Upon loading, the program checks to see that the
the BIOS vector table pointed to by the word at location
0001H is valid, i.e. is a table of JMP instructions containing
at least 16 entries.  If an error is detected, the program
will display an error message on the console and attempt to
warm-boot CP/M.
	If found, the BIOS vector table is copied into the
program segment which will remain active during unspooling
so that subsequent application programs running concurrently
with UNSPOOL will still have access to the BIOS.
	The address of the old BIOS vector table, the BDOS
entry address, and the CCP return address (from the top of the
stack on entry) are saved in memory.
	The "dev" parameter from the command line is checked.
If not valid, an error message is typed and control returns
to the CCP.
	The file named in the command line is opened for
input.  If not present, the filename is echoed to the console
followed by a "?" and control returns to CCP.
	If the drive is not explicit, the current default
drive number is recorded internally in case the default drive
is changed while UNSPOOL is active.
	The current user number and IOBYTE values are checked
and stored internally so that if the user number is changed,
UNSPOOL will still be able to read the input file.  If the
device is changed (using STAT LST:=TTY: for example) unspool
will continue to use the physical device in effect at the
time the program was initiated.  Any application programs
will, however, use the new values of the user number and the
new physical device assignments.
	If no errors were detected, the active program segment
which monitors all calls to BDOS is relocated into high memory
just below the CCP.  This reduces the available user program
area by 2.75 K:  3 pages for the UNSPOOL supervisor segment,
and 8 pages for the CCP which is commonly overwritten by user
program buffers.  The BOOT and BDOS jumps in low memory are
modified to protect the CCP and UNSPOOL supervisor segment.
	Control is then returned to the console.  Normal
CP/M operation will then be possible. Characters will be
sent from the input file to the output device whenever the
console is idle.

	Whenever an application program or the CCP requests
console input using BDOS functions 1 or 10, the supervisor
segment intercepts these requests and checks to see if the
console is idle.  If it is, characters are transferred from
the input file to the output device until the console becomes
ready, i.e. a key is actually pressed.  At that time the
BDOS function is executed normally, and control returns to the
application program.
	If a jump to BOOT is attempted, this is also
intercepted by the UNSPOOL supervisor segment.  The message
"Unspooling in progress" is displayed on the console, and
no actual boot takes place.  Control is returned to the
protected copy of the CCP instead.  Before returning, a disk
reset is performed and the default DMA address is reset to
0080H to simulate a true warm-boot as closely as possible.
	When the input file is completely transferred, or
a 1AH end-of-file character is detected, the supervisor
becomes inactive, and passes on all BDOS requests immediately,
without checking console status.  When the next warm-boot
request is detected, the supervisor removes itself from memory
by executing a true warm-boot, and informs the operator with
the message "UNSPOOL completed.".

NOTES:

	While UNSPOOL makes every effort to restore the values
of the DMA address, USER number, IOBYTE, and default disk drive
before returning control to the program, a hardware reset may
leave these values in an undetermined state if unspooling was
actually taking place at the time.
	The supervisor will not intercept a call to BDOS
function 0.  This will cause a true warm boot to occurr,
terminating unspool immediately.  Normally application programs
should reboot by jumping to location 0000H, not by calling
BDOS function 0.
	When function 10, Read Console Buffer is used, UNSPOOL
will transfer characters only until the first key is pressed.
At that time, no characters will be transferred until the
input line is completed by pressing a carriage return.
	UNSPOOL requires that the List Status function in
the BIOS was properly implemented at system installation time.
UNSPOOL will not send characters to the LST: device unless it
recieves a ready condition from the List Status routine.  If
the PUN: device is used, no status check is provided for by
CP/M, so a not-ready condition on the punch may cause the
system to hang up if PUN was specified on the command line.
See the CP/M Alteration Guide for a discussion of the BIOS
List Status routine.
	Although the console is polled frequently during the
unspooling of the file, some of the diskette operations may
take a second or two to complete, for example when a new extent
is opened.  Since the console is not polled during this period,
high speed typing may cause one or more characters to be lost.
This effect will vary depending upon the program being run,
the types of input reqests (character or line) it uses, and
the relative locations on diskette of the spool file and any
files in use by the program.  As a result, heads-down typing
is not reccommended while UNSPOOL is running.  Some experience
with UNSPOOL will teach the user when caution is required.

INSTALLATION:

	The source file is written for assembly with the
MAC assembler.  The .HEX file produced is LOADed to a .COM
file and executed just as any normal program.  Relocation is
done at execution time as described above.
	If the assembly option EXPAND is set to TRUE, tab
characters in the input file will be expanded to spaces with
assumed tab stops at every eighth print position.  This option
should be set to FALSE if the printer driver or the printer
itself can properly handle the tab character.  If the option
PHYSBS is set to TRUE, a backspace character will cause the
tab expansion algorithm to recognize backspace characters
and decrement the column count when a backspace is encountered
in the input file.  This option should be set to FALSE if
backspace characters are ignored by the printer.  All other
control codes except carriage return are assumed to be non-
printing, and are ignored by the algorithm.
	If tab expansion is included, the version number
in the signon message will be followed by "/T".

			Gary Novosielski

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