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380 lines
15 KiB
Plaintext
380 lines
15 KiB
Plaintext
.ec^
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.na
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.ll60
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.m11
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.m22
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.m48
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.fo ''-%-
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.pn 5
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.pi 0
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.br
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.np
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.ce
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CHAPTER 8 - DOS PROGRAM LOGIC
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.sp1
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This chapter will take a detailed
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look at the operation of the DOS
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program itself to aid the APPLE user
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in understanding it and to help him
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to make intelligent use of its
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facilities. Each subroutine and group
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of variables or constants will be
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covered separately by storage
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address. The enterprising programmer
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may wish to create a disassembly of
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DOS on his printer and transfer the
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annotations given here directly to
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such a listing. Addresses used will
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be for DOS 3.3 and for a 48K master
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diskette version of DOS. Slot 6 is
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assumed. Unless specifically
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indicated by a $ character, lengths
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are given in decimal, addresses in
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hexadecimal (base 16).
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.sp1
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DISK II CONTROLLER CARD ROM - BOOT 0
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.SP1
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.pi0
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.ul
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ADDRESS
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.np
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C600-C65B This routine is the first code executed when a disk
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is to be booted. It receives control via PR#6 or
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C600G or 6 control-P.
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Dynamically build a translate table for converting
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disk codes to six bit hex at location $356-$3FF.
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Call an RTS instruction in the monitor ROM and
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extract the return address from the stack to find out
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the address of this controller card ROM.
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Use this address to determine the slot number of this
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drive by shifting $Csxx.
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Save the slot number times 16 ($s0)
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Clear disk I/O latches, set read mode, select drive
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1, turn disk drive on.
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Pull disk arm back over 80 tracks to recalibrate the
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arm to track zero.
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Set up parms to read sector zero on track zero to
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location $800.
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Execution falls through into a general sector read
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subroutine at C65C.
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.np
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C65C-C6FA This subroutine reads the sector number stored at
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$3D on the track indicated by $41 to the address
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stored at $26,$27.
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Look for D5/AA/96 sector address header on the disk.
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If D5/AA/AD is found and sector data was wanted, go
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to C6A6.
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C683 Handle a sector address block.
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Read three double bytes from the disk and combine
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them to obtain the volume, track, and sector number
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of the sector being read from the disk at this time.
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Store the track at $40.
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Compare the sector found to the sector wanted and the
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track found to the track wanted.
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If no match, go back to C65C.
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Otherwise, if sector is correct, go to C65D to find
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the sector data itself.
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C6A6 Handle sector data block.
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Read the 85 bytes of secondary data to $300-$355.
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Read 256 bytes of primary data to the address stored
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at $26,$27.
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Verify that the data checksum is valid.
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If not, start over at C65C.
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"Nibbilize" the primary and secondary data together
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into the primary data buffer ($26,$27).
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Increment $27 (address page of read data) and $3D
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(sector number to be read) and check against $800
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to see if additional sectors need to be read.
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If so, reload slot*16 and go back to C65C to read
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next sector. (This feature is not used when loading
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DOS but is used when loading from a BASICS diskette.)
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Otherwise, go to $801 to begin executing the second
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stage of the bootstrap.
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.sp1
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FIRST RAM BOOTSTRAP LOADER - BOOT 1
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.sp1
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.Ul
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ADDRESS
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.np
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0801-084C This routine loads the second RAM loader, Boot 2,
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including RWTS, into memory and jumps to it.
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If this is not the first entry to Boot 1, go to $81F.
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Get slot*16 and shift down to slot number.
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Create the address of the ROM sector read subroutine
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(C65C in our case) and store it at $3E,$3F.
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Pick up the first memory page in which to read Boot 2
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from location $8FE, add the length of Boot 2 in
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sectors from $8FF, and set that value as the first
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address to which to read (read last page first).
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081F Get sector to read, if zero, go to $839.
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Translate theoretical sector number into physical
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sector number by indexing into skewing table at $84D.
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Decrement theoretical sector number (8FF) for next
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iteration through.
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Set up parameters for ROM subroutine (C65C) and
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jump to it. It will return to $801 when the sector
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has been read.
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0839 Adjust page number at 8FE to locate entry point of
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Boot 2.
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Perform a PR#0 and IN#0 by calling the monitor.
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Initialize the monitor (TEXT mode, standard window,
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etc.)
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Get slot*16 again and go to Boot 2 ($3700 for a
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master disk, $B700 in its final relocated location).
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.sp1
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DOS 3.3 MAIN ROUTINES
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.SP1
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.Ul
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ADDRESS
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.np
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9D00-9D0F Relocatable address constants
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9D00 Address of first DOS buffer at its file name field.
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9D02 Address of the DOS keyboard intercept routine.
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9D04 Address of the DOS video intercept routine.
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9D06 Address of the primary file name buffer.
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9D08 Address of the secondary (RENAME) file name buffer.
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9D0A Address of the range length parameter used for LOAD.
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9D0C Address of the DOS load address ($9D00).
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9D0E Address of the file manager parameter list.
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.np
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9D10-9D1C DOS video (CSWL) intercept's state handler address
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table. States are used to drive the handling of DOS
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commands as they appear as output of PRINT statements
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and this table contains the address of the routine
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which handles each state from state 0 to state 6.
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.np
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9D1E-9D55 Command handler entry point table. This table
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contains the address of a command handler subroutine
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for each DOS command in the following standard order:
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INIT A54F
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LOAD A413
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SAVE A397
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RUN A4D1
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CHAIN A4F0
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DELETE A263
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LOCK A271
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UNLOCK A275
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CLOSE A2EA
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READ A51B
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EXEC A5C6
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WRITE A510
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POSITION A5DD
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OPEN A2A3
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APPEND A298
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RENAME A281
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CATALOG A56E
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MON A233
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NOMON A23D
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PR# A229
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IN# A22E
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MAXFILES A251
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FP A57A
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INT A59E
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BSAVE A331
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BLOAD A35D
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BRUN A38E
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VERIFY A27D
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.np
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9D56-9D61 Active BASIC entry point vector table. The addresses
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stored here are maintained by DOS such that they
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apply to the current version of BASIC running.
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9D56 Address of CHAIN entry point to BASIC.
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9D58 Address of RUN.
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9D5A Address of error handler.
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9D5C Address of BASIC coldstart.
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9D5E Address of BASIC warmstart.
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9D60 Address of BASIC relocate (APPLESOFT only).
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.np
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9D62-9D6B Image of the entry point vector for INTEGER BASIC.
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This image is copied to 9D56 if INTEGER BASIC is made
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active.
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.np
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9D6C-9D77 Image of the entry point vector for the ROM version
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of APPLESOFT.
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.np
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9D78-9D83 Image of the entry point vector for the RAM version
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of APPLESOFT.
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.np
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9D84-9DBE DOS coldstart entry routine.
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Get the slot and drive numbers and store as default
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values for command keywords.
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Copy APPLESOFT ROM or INTEGER BASIC entry point
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vector into current BASIC entry point vector.
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Remember which BASIC is active.
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Go to 9DD1.
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.np
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9DBF-9DE9 DOS warmstart entry routine.
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Get the remembered BASIC type and set the ROM card
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as necessary (calls A5B2).
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9DD1 Remember whether entry is coldstart or warmstart
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Call A851 to replace DOS keyboard and video
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intercepts.
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Set NOMON C,I,O.
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Set video intercept handler state to 0.
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Coldstart or warmstart the current BASIC (exit DOS).
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(DOS will next gain control when BASIC prints its
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input prompt character)
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.np
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9DEA-9E50 First entry processing for DOS. This routine is
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called by the keyboard intercept handler when the
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first keyboard input request is made by BASIC after
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a DOS coldstart.
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If RAM APPLESOFT is active, copy its entry point
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vector to the active BASIC entry point vector and
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blank out the primary file name buffer so that no
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HELLO file will be run.
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Set MAXFILES to 3 by default.
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Call A7D4 to build the DOS file buffers.
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If an EXEC was active, close the EXEC file
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Set the video intercept state to 0 and indicate
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warmstart status by calling A75B.
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If the last command executed was not INIT (this DOS
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was not just booted), go to 9E45.
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Otherwise, copy an image of the DOS jump vector to
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$3D0-$3FF.
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Point $3F2,$3F3 to DOS warmstart routine.
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Set the AUTOSTART ROM power-up byte since the RESET
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handler address was changed.
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Set the command index for RUN (to run the HELLO file)
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and go to A180 to execute it.
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9E45 See if there is a pending command.
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If so, go to A180 to execute it. Otherwise, return
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to caller.
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.np
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9E51-9E7F An image of the DOS 3-page jump vector which the
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above routine copies to $3D0-$3FF. See Chapter 5 for
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a description of its contents.
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.np
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9E81-9EB9 DOS keyboard intercept routine.
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Call 9ED1 to save the registers at entry to DOS.
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If not coldstarting or reading a disk file,
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go to 9E9E.
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Get value in A register at entry and echo it on the
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screen (erases flashing cursor).
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If in read state (reading a file) go to A626 to get
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next byte from disk file.
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Otherwise, call 9DEA to do first entry processing.
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Put cursor on screen in next position.
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If EXECing, call A682 to get the next byte from the
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EXEC file.
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Set the video intercept state to 3 (input echo).
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Call 9FBA to restore the registers at entry to DOS.
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Call the true keyboard input routine.
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Save the input character so that it will be restored
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with the registers in the A register.
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Do the same with the new X register value.
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Exit DOS via 9FB3.
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.np
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9EBA-9EBC A jump to the true KSWL handler routine.
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.np
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9EBD-9ED0 DOS video intercept routine.
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Call 9ED1 to save the registers at entry to DOS.
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Get the video intercept state and, using it as an
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index into the state handler table (9D11), go to
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the proper handler routine, passing it the character
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being printed.
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.np
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9ED1-9EEA Common intercept save registers routine.
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Save the A, X, Y, and S registers at AA59-AA5C.
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While in DOS, restore the true I/O handlers (KSWL and
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CSWL) to $36-$39.
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Return to caller.
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.np
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9EEB-9F11 State 0 output handler. --start of line--
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If a RUN command was interrupted (by loading RAM
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APPLESOFT) go to 9F78 to complete it.
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If read flag is on (file being read) and output is a
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"?" character (BASIC INPUT), go to state 6 to skip
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it.
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If read flag is on and output is prompt character
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($33) go to state 2 to ignore the line.
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Set state to 2 (ignore non-DOS command) just in case.
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If output character is not a control-D, go to
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state 2.
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Otherwise, set state to 1 (collect possible DOS
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command), set line index to zero, and fall through
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to state 1.
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.np
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9F12-9F22 State 1 output handler. --collect DOS command--
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Using line index, store character in input buffer at
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$200.
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Increment line index.
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If character is not a carriage return, exit DOS
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via 9F95 (echo character on screen if MON I).
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Otherwise, go to command scanner at 9FCD.
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.np
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9F23-9F2E State 2 output handler. --non-DOS command ignore--
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If the character is not a carriage return, exit DOS
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via 9FA4 (echo character on screen).
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Otherwise, set state back to 0 and exit DOS via
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9FA4.
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.np
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9F2F-9F51 State 3 output handler. --INPUT statement handler--
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Set state to 0 in case INPUT ends.
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If character is not a carriage return, echo it on
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screen as long as EXEC is not in effect with NOMON I
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but exit DOS in any case. (KSWL will set state=3)
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Otherwise, call A65E to see if BASIC is executing a
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program or is in immediate mode. If EXEC is running
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or if BASIC is in immediate mode, go to state 1 to
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collect the possible DOS command.
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Otherwise, exit DOS, echoing the character as
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appropriate.
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.np
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9F52-9F60 State 4 output handler. --WRITE data to a file--
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If the character is a carriage return, set state to
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5 (start of write data line).
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Call A60E to write the byte to the disk file.
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Exit DOS with echo on screen if MON O.
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.np
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9F61-9F70 State 5 output handler. --Start of WRITE data line--
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If the character is a control-D, go to state 0 to
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immediately exit write mode.
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If the character is a line feed, write it and exit,
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staying in state 5.
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Otherwise, set the state to 4 and go to state 4.
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.np
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9F71-9F77 State 6 output handler. --Skip prompt character--
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Set state to 0.
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Exit DOS via 9F9D (echo if MON I).
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.np
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9F78-9F82 Finish RUN command, interrupted by APPLESOFT RAM LOAD
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Reset the "RUN interrupted" flag.
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Call A851 to replace the DOS CSWL/KSWL intercepts.
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Go to A4DC to complete the RUN command.
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.np
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9F83-9F94 DOS command scanner exit to BASIC routine.
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If first character of command line is control-D,
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go to echo exit (9F95).
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Otherwise, set things up so BASIC won't see the DOS
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command by passing a zero length line (only a
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carriage return). Fall through to echo exit.
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.np
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9F95-9FB0 Echo character on screen (conditionally) and exit DOS
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9F95 Echo only if MON C set, otherwise, go to 9FB3.
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9F99 Echo only if MON O set, otherwise, go to 9FB3.
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9F9D Echo only if MON I set, otherwise, go to 9FB3.
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9FA4 Always echo character.
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Call 9FBA to restore registers at entry to DOS.
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Call 9FC5 to echo character on screen.
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Save contents of the registers after echoing.
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Fall through to DOS exit routine.
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.np
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9FB3-9FC4 DOS exit routine and register restore.
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Call A851 to put back DOS KSWL/CSWL intercepts.
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Restore S (stack) register from entry to DOS.
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9FBA DOS register restore subroutine.
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Restore registers from first entry to DOS and return
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to caller.
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.np
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9FC5-9FC7 A jump to the true CSWL routine.
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.np
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9FC8-9FCC Skip a line on the screen.
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Load a carriage return into the A register and
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call 9FC5 to print it.
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.np
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9FCD-A179 DOS command parse routine.
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.br
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.nx ch8.1
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