mirror of
https://github.com/iKarith/beneath-apple-dos.git
synced 2024-12-22 07:30:43 +00:00
380 lines
15 KiB
Plaintext
380 lines
15 KiB
Plaintext
.ec^
|
|
.na
|
|
.ll60
|
|
.m11
|
|
.m22
|
|
.m48
|
|
.fo ''-%-
|
|
.pn5
|
|
.pi0
|
|
.br
|
|
.np
|
|
.ce
|
|
CHAPTER 8 - DOS PROGRAM LOGIC
|
|
.sp1
|
|
|
|
This chapter will take a detailed
|
|
look at the operation of the DOS
|
|
program itself to aid the APPLE user
|
|
in understanding it and to help him
|
|
to make intelligent use of its
|
|
facilities. Each subroutine and group
|
|
of variables or constants will be
|
|
covered separately by storage
|
|
address. The enterprising programmer
|
|
may wish to create a disassembly of
|
|
DOS on his printer and transfer the
|
|
annotations given here directly to
|
|
such a listing. Addresses used will
|
|
be for DOS 3.3 and for a 48K master
|
|
diskette version of DOS. Slot 6 is
|
|
assumed. Unless specifically
|
|
indicated by a $ character, lengths
|
|
are given in decimal, addresses in
|
|
hexadecimal (base 16).
|
|
.sp1
|
|
DISK II CONTROLLER CARD ROM - BOOT 0
|
|
.sp1
|
|
.pi0
|
|
.ul
|
|
ADDRESS
|
|
.np
|
|
C600-C65B This routine is the first code executed when a disk
|
|
is to be booted. It receives control via PR#6 or
|
|
C600G or 6 control-P.
|
|
Dynamically build a translate table for converting
|
|
disk codes to six bit hex at location $356-$3FF.
|
|
Call an RTS instruction in the monitor ROM and
|
|
extract the return address from the stack to find out
|
|
the address of this controller card ROM.
|
|
Use this address to determine the slot number of this
|
|
drive by shifting $Csxx.
|
|
Save the slot number times 16 ($s0)
|
|
Clear disk I/O latches, set read mode, select drive
|
|
1, turn disk drive on.
|
|
Pull disk arm back over 80 tracks to recalibrate the
|
|
arm to track zero.
|
|
Set up parms to read sector zero on track zero to
|
|
location $800.
|
|
Execution falls through into a general sector read
|
|
subroutine at C65C.
|
|
.np
|
|
C65C-C6FA This subroutine reads the sector number stored at
|
|
$3D on the track indicated by $41 to the address
|
|
stored at $26,$27.
|
|
Look for D5/AA/96 sector address header on the disk.
|
|
If D5/AA/AD is found and sector data was wanted, go
|
|
to C6A6.
|
|
C683 Handle a sector address block.
|
|
Read three double bytes from the disk and combine
|
|
them to obtain the volume, track, and sector number
|
|
of the sector being read from the disk at this time.
|
|
Store the track at $40.
|
|
Compare the sector found to the sector wanted and the
|
|
track found to the track wanted.
|
|
If no match, go back to C65C.
|
|
Otherwise, if sector is correct, go to C65D to find
|
|
the sector data itself.
|
|
C6A6 Handle sector data block.
|
|
Read the 85 bytes of secondary data to $300-$355.
|
|
Read 256 bytes of primary data to the address stored
|
|
at $26,$27.
|
|
Verify that the data checksum is valid.
|
|
If not, start over at C65C.
|
|
"Nibbilize" the primary and secondary data together
|
|
into the primary data buffer ($26,$27).
|
|
Increment $27 (address page of read data) and $3D
|
|
(sector number to be read) and check against $800
|
|
to see if additional sectors need to be read.
|
|
If so, reload slot*16 and go back to C65C to read
|
|
next sector. (This feature is not used when loading
|
|
DOS but is used when loading from a BASICS diskette.)
|
|
Otherwise, go to $801 to begin executing the second
|
|
stage of the bootstrap.
|
|
.sp1
|
|
FIRST RAM BOOTSTRAP LOADER - BOOT 1
|
|
.sp1
|
|
.ul
|
|
ADDRESS
|
|
.np
|
|
0801-084C This routine loads the second RAM loader, Boot 2,
|
|
including RWTS, into memory and jumps to it.
|
|
If this is not the first entry to Boot 1, go to $81F.
|
|
Get slot*16 and shift down to slot number.
|
|
Create the address of the ROM sector read subroutine
|
|
(C65C in our case) and store it at $3E,$3F.
|
|
Pick up the first memory page in which to read Boot 2
|
|
from location $8FE, add the length of Boot 2 in
|
|
sectors from $8FF, and set that value as the first
|
|
address to which to read (read last page first).
|
|
081F Get sector to read, if zero, go to $839.
|
|
Translate theoretical sector number into physical
|
|
sector number by indexing into skewing table at $84D.
|
|
Decrement theoretical sector number (8FF) for next
|
|
iteration through.
|
|
Set up parameters for ROM subroutine (C65C) and
|
|
jump to it. It will return to $801 when the sector
|
|
has been read.
|
|
0839 Adjust page number at 8FE to locate entry point of
|
|
Boot 2.
|
|
Perform a PR#0 and IN#0 by calling the monitor.
|
|
Initialize the monitor (TEXT mode, standard window,
|
|
etc.)
|
|
Get slot*16 again and go to Boot 2 ($3700 for a
|
|
master disk, $B700 in its final relocated location).
|
|
.sp1
|
|
DOS 3.3 MAIN ROUTINES
|
|
.sp1
|
|
.ul
|
|
ADDRESS
|
|
.np
|
|
9D00-9D0F Relocatable address constants
|
|
9D00 Address of first DOS buffer at its file name field.
|
|
9D02 Address of the DOS keyboard intercept routine.
|
|
9D04 Address of the DOS video intercept routine.
|
|
9D06 Address of the primary file name buffer.
|
|
9D08 Address of the secondary (RENAME) file name buffer.
|
|
9D0A Address of the range length parameter used for LOAD.
|
|
9D0C Address of the DOS load address ($9D00).
|
|
9D0E Address of the file manager parameter list.
|
|
.np
|
|
9D10-9D1C DOS video (CSWL) intercept's state handler address
|
|
table. States are used to drive the handling of DOS
|
|
commands as they appear as output of PRINT statements
|
|
and this table contains the address of the routine
|
|
which handles each state from state 0 to state 6.
|
|
.np
|
|
9D1E-9D55 Command handler entry point table. This table
|
|
contains the address of a command handler subroutine
|
|
for each DOS command in the following standard order:
|
|
INIT A54F
|
|
LOAD A413
|
|
SAVE A397
|
|
RUN A4D1
|
|
CHAIN A4F0
|
|
DELETE A263
|
|
LOCK A271
|
|
UNLOCK A275
|
|
CLOSE A2EA
|
|
READ A51B
|
|
EXEC A5C6
|
|
WRITE A510
|
|
POSITION A5DD
|
|
OPEN A2A3
|
|
APPEND A298
|
|
RENAME A281
|
|
CATALOG A56E
|
|
MON A233
|
|
NOMON A23D
|
|
PR# A229
|
|
IN# A22E
|
|
MAXFILES A251
|
|
FP A57A
|
|
INT A59E
|
|
BSAVE A331
|
|
BLOAD A35D
|
|
BRUN A38E
|
|
VERIFY A27D
|
|
.np
|
|
9D56-9D61 Active BASIC entry point vector table. The addresses
|
|
stored here are maintained by DOS such that they
|
|
apply to the current version of BASIC running.
|
|
9D56 Address of CHAIN entry point to BASIC.
|
|
9D58 Address of RUN.
|
|
9D5A Address of error handler.
|
|
9D5C Address of BASIC coldstart.
|
|
9D5E Address of BASIC warmstart.
|
|
9D60 Address of BASIC relocate (APPLESOFT only).
|
|
.np
|
|
9D62-9D6B Image of the entry point vector for INTEGER BASIC.
|
|
This image is copied to 9D56 if INTEGER BASIC is made
|
|
active.
|
|
.np
|
|
9D6C-9D77 Image of the entry point vector for the ROM version
|
|
of APPLESOFT.
|
|
.np
|
|
9D78-9D83 Image of the entry point vector for the RAM version
|
|
of APPLESOFT.
|
|
.np
|
|
9D84-9DBE DOS coldstart entry routine.
|
|
Get the slot and drive numbers and store as default
|
|
values for command keywords.
|
|
Copy APPLESOFT ROM or INTEGER BASIC entry point
|
|
vector into current BASIC entry point vector.
|
|
Remember which BASIC is active.
|
|
Go to 9DD1.
|
|
.np
|
|
9DBF-9DE9 DOS warmstart entry routine.
|
|
Get the remembered BASIC type and set the ROM card
|
|
as necessary (calls A5B2).
|
|
9DD1 Remember whether entry is coldstart or warmstart
|
|
Call A851 to replace DOS keyboard and video
|
|
intercepts.
|
|
Set NOMON C,I,O.
|
|
Set video intercept handler state to 0.
|
|
Coldstart or warmstart the current BASIC (exit DOS).
|
|
(DOS will next gain control when BASIC prints its
|
|
input prompt character)
|
|
.np
|
|
9DEA-9E50 First entry processing for DOS. This routine is
|
|
called by the keyboard intercept handler when the
|
|
first keyboard input request is made by BASIC after
|
|
a DOS coldstart.
|
|
If RAM APPLESOFT is active, copy its entry point
|
|
vector to the active BASIC entry point vector and
|
|
blank out the primary file name buffer so that no
|
|
HELLO file will be run.
|
|
Set MAXFILES to 3 by default.
|
|
Call A7D4 to build the DOS file buffers.
|
|
If an EXEC was active, close the EXEC file
|
|
Set the video intercept state to 0 and indicate
|
|
warmstart status by calling A75B.
|
|
If the last command executed was not INIT (this DOS
|
|
was not just booted), go to 9E45.
|
|
Otherwise, copy an image of the DOS jump vector to
|
|
$3D0-$3FF.
|
|
Point $3F2,$3F3 to DOS warmstart routine.
|
|
Set the AUTOSTART ROM power-up byte since the RESET
|
|
handler address was changed.
|
|
Set the command index for RUN (to run the HELLO file)
|
|
and go to A180 to execute it.
|
|
9E45 See if there is a pending command.
|
|
If so, go to A180 to execute it. Otherwise, return
|
|
to caller.
|
|
.np
|
|
9E51-9E7F An image of the DOS 3-page jump vector which the
|
|
above routine copies to $3D0-$3FF. See Chapter 5 for
|
|
a description of its contents.
|
|
.np
|
|
9E81-9EB9 DOS keyboard intercept routine.
|
|
Call 9ED1 to save the registers at entry to DOS.
|
|
If not coldstarting or reading a disk file,
|
|
go to 9E9E.
|
|
Get value in A register at entry and echo it on the
|
|
screen (erases flashing cursor).
|
|
If in read state (reading a file) go to A626 to get
|
|
next byte from disk file.
|
|
Otherwise, call 9DEA to do first entry processing.
|
|
Put cursor on screen in next position.
|
|
If EXECing, call A682 to get the next byte from the
|
|
EXEC file.
|
|
Set the video intercept state to 3 (input echo).
|
|
Call 9FBA to restore the registers at entry to DOS.
|
|
Call the true keyboard input routine.
|
|
Save the input character so that it will be restored
|
|
with the registers in the A register.
|
|
Do the same with the new X register value.
|
|
Exit DOS via 9FB3.
|
|
.np
|
|
9EBA-9EBC A jump to the true KSWL handler routine.
|
|
.np
|
|
9EBD-9ED0 DOS video intercept routine.
|
|
Call 9ED1 to save the registers at entry to DOS.
|
|
Get the video intercept state and, using it as an
|
|
index into the state handler table (9D11), go to
|
|
the proper handler routine, passing it the character
|
|
being printed.
|
|
.np
|
|
9ED1-9EEA Common intercept save registers routine.
|
|
Save the A, X, Y, and S registers at AA59-AA5C.
|
|
While in DOS, restore the true I/O handlers (KSWL and
|
|
CSWL) to $36-$39.
|
|
Return to caller.
|
|
.np
|
|
9EEB-9F11 State 0 output handler. --start of line--
|
|
If a RUN command was interrupted (by loading RAM
|
|
APPLESOFT) go to 9F78 to complete it.
|
|
If read flag is on (file being read) and output is a
|
|
"?" character (BASIC INPUT), go to state 6 to skip
|
|
it.
|
|
If read flag is on and output is prompt character
|
|
($33) go to state 2 to ignore the line.
|
|
Set state to 2 (ignore non-DOS command) just in case.
|
|
If output character is not a control-D, go to
|
|
state 2.
|
|
Otherwise, set state to 1 (collect possible DOS
|
|
command), set line index to zero, and fall through
|
|
to state 1.
|
|
.np
|
|
9F12-9F22 State 1 output handler. --collect DOS command--
|
|
Using line index, store character in input buffer at
|
|
$200.
|
|
Increment line index.
|
|
If character is not a carriage return, exit DOS
|
|
via 9F95 (echo character on screen if MON I).
|
|
Otherwise, go to command scanner at 9FCD.
|
|
.np
|
|
9F23-9F2E State 2 output handler. --non-DOS command ignore--
|
|
If the character is not a carriage return, exit DOS
|
|
via 9FA4 (echo character on screen).
|
|
Otherwise, set state back to 0 and exit DOS via
|
|
9FA4.
|
|
.np
|
|
9F2F-9F51 State 3 output handler. --INPUT statement handler--
|
|
Set state to 0 in case INPUT ends.
|
|
If character is not a carriage return, echo it on
|
|
screen as long as EXEC is not in effect with NOMON I
|
|
but exit DOS in any case. (KSWL will set state=3)
|
|
Otherwise, call A65E to see if BASIC is executing a
|
|
program or is in immediate mode. If EXEC is running
|
|
or if BASIC is in immediate mode, go to state 1 to
|
|
collect the possible DOS command.
|
|
Otherwise, exit DOS, echoing the character as
|
|
appropriate.
|
|
.np
|
|
9F52-9F60 State 4 output handler. --WRITE data to a file--
|
|
If the character is a carriage return, set state to
|
|
5 (start of write data line).
|
|
Call A60E to write the byte to the disk file.
|
|
Exit DOS with echo on screen if MON O.
|
|
.np
|
|
9F61-9F70 State 5 output handler. --Start of WRITE data line--
|
|
If the character is a control-D, go to state 0 to
|
|
immediately exit write mode.
|
|
If the character is a line feed, write it and exit,
|
|
staying in state 5.
|
|
Otherwise, set the state to 4 and go to state 4.
|
|
.np
|
|
9F71-9F77 State 6 output handler. --Skip prompt character--
|
|
Set state to 0.
|
|
Exit DOS via 9F9D (echo if MON I).
|
|
.np
|
|
9F78-9F82 Finish RUN command, interrupted by APPLESOFT RAM LOAD
|
|
Reset the "RUN interrupted" flag.
|
|
Call A851 to replace the DOS CSWL/KSWL intercepts.
|
|
Go to A4DC to complete the RUN command.
|
|
.np
|
|
9F83-9F94 DOS command scanner exit to BASIC routine.
|
|
If first character of command line is control-D,
|
|
go to echo exit (9F95).
|
|
Otherwise, set things up so BASIC won't see the DOS
|
|
command by passing a zero length line (only a
|
|
carriage return). Fall through to echo exit.
|
|
.np
|
|
9F95-9FB0 Echo character on screen (conditionally) and exit DOS
|
|
9F95 Echo only if MON C set, otherwise, go to 9FB3.
|
|
9F99 Echo only if MON O set, otherwise, go to 9FB3.
|
|
9F9D Echo only if MON I set, otherwise, go to 9FB3.
|
|
9FA4 Always echo character.
|
|
Call 9FBA to restore registers at entry to DOS.
|
|
Call 9FC5 to echo character on screen.
|
|
Save contents of the registers after echoing.
|
|
Fall through to DOS exit routine.
|
|
.np
|
|
9FB3-9FC4 DOS exit routine and register restore.
|
|
Call A851 to put back DOS KSWL/CSWL intercepts.
|
|
Restore S (stack) register from entry to DOS.
|
|
9FBA DOS register restore subroutine.
|
|
Restore registers from first entry to DOS and return
|
|
to caller.
|
|
.np
|
|
9FC5-9FC7 A jump to the true CSWL routine.
|
|
.np
|
|
9FC8-9FCC Skip a line on the screen.
|
|
Load a carriage return into the A register and
|
|
call 9FC5 to print it.
|
|
.np
|
|
9FCD-A179 DOS command parse routine.
|
|
.br
|
|
.nx ch8.1
|