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-=-=-=-=-=-=-
- *****************************************************************
- *
- DOS's warmstart routine *
- *
- ----------------------------------------------------------------*
- *
- The DOS cold- and warmstart routines represent the focal *
- points from which DOS begins processing information. It *
- therefore seems logical that the novice should launch his trek *
- into DOS from these routines. However, the cold- and warm- *
- start routines are difficult to understand because: *
- 1) Program execution bounces back and forth between DOS, *
- BASIC and monitor ROM. *
- 2) Both the cold- and warmstart routines are riddled with *
- references to an obscure version of Applesoft that most *
- people don't even realize exits. *
- 3) The DOS coldstart routine uses part of the warmstart *
- routine. In order to distinguish between these two *
- execution patterns, it is important to pay close *
- attention to the condition of the status register and *
- several different flags. *
- *
- ABOUT PROGRAM EXECUTION AND THE I/O HOOKS. *
- The interconnection between DOS, BASIC and monitor ROM is *
- accomplished by DOS's control over the input (KSW, $36,$37) *
- and output (CSW, $38,$39) hooks. (These hooks are collectively*
- referred to as the I/O hooks, the KSW/CSW hooks or the *
- keyboard/character switches.) In order to understand how DOS *
- controls these hooks, lets first see what happens when DOS is *
- NOT present: *
- - Ordinarily, data output flows through a monitor ROM routine *
- called "COUT" ($FDED). COUT contains a "JMP (CSW)"instruc- *
- tion. CSW points to the address of the peripheral to which *
- output should be sent. For instance, if output is destined *
- for the screen, CSW points to a monitor routine called *
- "COUT1" ($FDF0). After COUT1 does some homework, it sends *
- the character to the screen. Similarly, input normally *
- flows through the "RDKEY" ($FD0C) routine located in monitor *
- ROM. This routine contains a "JMP (KSW)" instruction. KSW *
- normally points to the monitor routine known as "KEYIN" *
- ($FD1D). KEYIN accepts input from the keyboard. *
- Now, let's put DOS back into the picture: *
- - When a coldstart is done, the INITIOHK ($A851) routine in *
- DOS initializes the I/O hooks to point to DOS's own input *
- (INPTINCP, $9E81) and output (OPUTINCP, $9E8D) handlers. *
- Therefore, when DOS is up, any routine that requests input *
- or output, must go through DOS's own I/O handlers to be *
- screened. The I/O handlers decide whether the input is to *
- be taken from the keyboard or the disk and whether output *
- should be sent to the screen, the disk, the printer or any *
- other output device. For example, let's assume that we are *
- running a BASIC program that calls for a character to be *
- printed on the screen. When BASIC's "PRINT" statement is *
- encountered, execution flows to the "JMP (CSW)" instruction *
- in the monitor at COUT ($FDED). Because the output hook *
- (CSW) points to DOS's output handler, execution flows to *
- OPUTINCP ($9E8D). OPUTINCP looks at the command line and *
- discovers that the character is to be sent to the screen. *
- It then calls PREP4DOS ($9ED1) to repoint the output hook at *
- the true output handler (COUT1, $FDF0) and JSR's to COUT1. *
- After COUT1 puts the character on the screen, execution *
- returns to DOS. DOS does some homework and then execution *
- flows back to BASIC. Before DOS is exited however, it again *
- calls the INITIOHK routine to reset the I/O hooks to point *
- at DOS'S own I/O handlers. *
- In otherwords, DOS acts like and omnipotent peeping Tom. He *
- screens all input and output and then takes whatever action he *
- deems appropriate. *
- *
- PARLEZ VOUS APPLESOFT? *
- The first three models of Apple II computers were based *
- on two different versions of ROM. Old Apple II's contained *
- Integer basic in ROM whereas the newer Apple II+/IIe's were *
- built with Applesoft basic in ROM. In order to accommodate *
- both types of machines and their hapless programmers, Apple *
- made the DOS Master disk bilingual. When you boot with this *
- disk, DOS determines what kind of machine you're using and *
- what language to load on the RAM card. For example, if you *
- are using a II+ or IIe, the sytem master disk automatically *
- runs the "HELLO" program. The "HELLO" program then loads a *
- file called "INTBASIC" onto the RAM card. (INTBASIC is a *
- binary file which represents an image of the Integer basic *
- language.) Similarly, if you're using an old Apple II *
- machine, the sytem master will run an Integer program *
- (confusingly called, "APPLESOFT") which loads a file called *
- "FPBASIC" onto the language card. (FPBASIC is a binary file *
- which represents an image of Applesoft Floating Point Basic.) *
- Because this ram-resident version of Applesoft has gone *
- through several evolutionary stages, it is referred to in the *
- literature by several different names: disk-based Applesoft, *
- Applesoft RAM, cassette Applesoft, RAM Applesoft and A(RAM). *
- Therefore, because the language card can contain a *
- different language than the motherboard, the cold- and warm- *
- start routines must determine not only which language is *
- presently active, but also if the active language is on the *
- card or motherboard. *
- *
- FLAGS AND EXECUTION PATTERNS. *
- The status register is used to distinguish between the *
- cold- and warmstart execution patterns. In some cases (ex. *
- CMWRMCLD,$9DD1), the carry flag is used to determine if a *
- cold- or warmstart is being executed. However, in other cases *
- (ex. OPUTINCP, $9E8D and INPTINCPT, $9E81), a specific memory *
- location is used as a flag. Because several flags appear to *
- have similar connotations but are set and tested at different *
- times, one must keep close tabs on the different flag *
- conditions: *
- (AA51) *
- CONDNFLG = I/O condition flag. *
- = $00 = warmstart. *
- = $01 = reading a file. *
- = $C0 = using A(RAM). *
- (AA52) *
- OPUTCOND = character output condition flag. *
- = $00 = evaluate start of input line. *
- = $01 = got a DOS control character, so collect *
- the DOS command. *
- = $02 = not a DOS command, so just print a <cr> *
- and return to the caller. *
- = $03 = get ready to process an INPUT statement. *
- = $04 = writing data to the disk. *
- = $05 = evaluate the first char of the data line *
- read from the disk. *
- = $06 = ignore a question mark prompt & reset to *
- condition 0. *
- (AAB3) *
- EXECFLAG = non-zero value (actually first char of the *
- name of the exec file) = presently EXECing. *
- = $00 = not EXECing a file. *
- (AAB6) *
- ACTBSFLG = active basic flag. *
- = $00 = integer. *
- = $40 = A(ROM). *
- = $80 = A(RAM). *
- (AAB7) *
- RUNTRUPT = run intercept flag. *
- = $00 = RUN command was NOT interrupted. *
- = $40 = RUN command was interrupted to load *
- a file when using A(ROM). *
- = $80 = RUN command was interrupted to load *
- a file when using A(RAM). *
- (E000) *
- BASICCLD = BASIC's coldstart routine. *
- (First byte distinguishes type of ROM used.) *
- = $20 = opcode for "JSR", denotes Integer. *
- = $40 = opcode for "JMP", denotes A(ROM). *
- *
- To help keep things in perspective, the general features *
- of the cold- and warmstart routines are described below: *
- *
- COLDSTART - determine what language & ROM is being used *
- and fill in the active basic entry point *
- vector table accordingly. *
- - reset the I/O hooks so that DOS can intercept *
- all input & output. *
- - simulate a "NOMON" command. *
- - rebuild the DOS buffers (resetting HIMEM, *
- discarding strings and wiping out the prgm). *
- - print a prompt and wait for input. *
- WARMSTART - reset the language card to the language used *
- when DOS was last cold started. *
- - reset the I/O hooks so DOS can intercept all *
- input and output. *
- - simulate a "NOMON command. *
- - (note that the program and variables are left *
- intact.) *
- *
- ================================================================*
NOTE: THE FOLLOWING DISASSEMBLY IS INCOMPLETE. It does not
contain all possible ramifications associated with the
warmstart routine.
(9DBF)
DOSWARM LDA ACTBSFLG ;See which language is up.
(9DC2) BNE CKBASIC ;Branch if A(ROM), #$40 or A(RAM), #$80.
(9DC4) LDA #$20 ;(a) = opcode for "JSR" instruction.
(9DC6) BNE DTRMNBSC ;ALWAYS.
- Active basic flag denoted that a
- version of Applesoft was active,
- so now check if dealing with
- A(RAM) or A(ROM).
(9DC8)
CKBASIC ASL ;Multiply code times 2.
(9DC9) BPL FORWARM ;Branch if A(RAM) (ie. A(RAM) yeilds
;$40 * 2 = $80 & A(ROM) yeilds $80 * 2 = $00.)
(9DCB) LDA #$4C ;(a) = opcode for "JMP" instruction.
DTRMNBSC JSR SETROM ;Select the desired basic.
(9DCD)
* Test card or motherboard to insure that the
* device containing the ROM version we want is
* selected. BASICCLD ($E000) contains a "JMP"
* or a "JSR" instruction if we are dealing with
* FP or INTEGER ROM respectively.
(A5B2)
SETROM CMP BASICCLD ;Test card or motherboard. That is, test
;whichever device is presently selected.
(A5B5) BEQ DVICERTN ;The language wanted is resident on the
;present device.
* The language wanted was not on the device
* selected, so specifically test the card
* in slot 0. NOTE: We could change the
* "$C080" to "$Cs80" to enable the card to
* be located in a different slot (s = slot #).
(A5B7) STA $C080 ;Read enable slot 0.
CMP BASICCLD ;Check the identifying byte.
(A5BD) BEQ DVICERTN ;Branch if the ROM language we wanted
;is on the card.
* ROM version wanted was not on the card.
* However, we may have just tested the card
* twice, so now specifically test the motherboard.
(A5BF) STA $C081 ;Test the motherboard.
CMP BASICCLD ;Check the identifying byte.
DVICERTN RTS ;Exit with switches pointing at the last
(A5C5) ;device tested. If the desired language is
;present, the switches are left positioned
;correctly.
(9DD0)
FORWARM CLC ;(c) = 0, signal for warmstart.
CMWRMCLD PHP ;Save (c) denoting if warm or cold starting.
(9DD2) JSR INITIOHK ;Initialize the I/O hooks.
* Initialize the I/O hooks so that DOS intercepts
* all input & output. For instance, if a routine
* encounters a "COUT JMP (CSW)", then execution will
* actually flow to DOS's output routine (OPUTINCP,
* $9EBD). Similarly, any routine that refers to
* "RDKEY JMP (KSW)" will actually jump to DOS's
* input routine (INPTINCP, $9E81).
*
* The true (ie. normal) hooks are saved, ex:
* KSW: KEYIN --> KSWTRUE: KEYIN.
* CSW: COUT1 --> CSWTRUE: COUT1.
* The intercepts are then set as follows:
* ADINPTCP: INPTINCP --> KSW: INPTINCP.
* ADOPUTCP: OPUTINCP --> CSW: OPUTINCP.
* Check if the input hook needs to be reset.
(A851)
INITIOHK LDA KSW+1
CMP ADINPTCP+1
(A856) BEQ CKOUTHK ;Input hook already points to DOS's
;input handler, so go check output hook.
* Reset the input hook to point to DOS.
(A858) STA KSWTRUE+1 ;KSW: KEYIN --> KSWTRUE: KEYIN.
LDA KSW
STA KSWTRUE
LDA ADINPTCP ;ADINPTCP: INPTINCP --> KSW: INPTINCP.
STA KSW
LDA ADINPTCP+1
(A868) STA KSW+1
* Check if the output hook needs to be reset.
(A86A)
CKOUTHK LDA CSW+1
CMP ADOPUTCP+1
(A86F) BEQ SETHKRTN ;Output hook already points to DOS's
;output handler, so go exit.
* Reset the output hook to point to DOS.
(A871) STA CSWTRUE+1 ;CSW: COUT1 --> CSWTRUE: COUT1.
LDA CSW
STA CSWTRUE
LDA ADOPUTCP ;ADOPUTCP: OPUTINCP --> CSW: OPUTINCP.
STA CSW
LDA ADOPUTCP+1
STA CSW+1
SETHKRTN RTS
(A883)
(9DD5) LDA #0
(9DD7) STA CIOCUMUL ;Simulate a "NOMON" command. Note, we can
;NOP out this instruction to defeat the
;"NOMONCIO" during warm- or coldstarts.
(9DDA) STA OPUTCOND ;SET CONDITION 0.
PLP ;Get status back off the stack.
ROR ;Use it to set CONDNFLG=$00 for warmstart
STA CONDNFLG ;or CONDNFLG=$80 for coldstart.
(9DE2) BMI LANGCOLD ;Branch if doing coldstart.
(9DE4)
LANGWARM JMP (TOWRMVEC) ;Jumps to BASIC's warmstart routine
------------ ;(RESTART) at $D43C.
- NOTE: YOU ARE LEAVING THE COMFORTABLE WORLD
- OF DOS AND ENTERING THE MURKY REALM OF BASIC.
- BASIC's warmstart routine.
- GO THROUGH A MILLION STEPS TO PRINT
- A CARRIAGE RETURN.
(D43C)
RESTART JSR CRDO
(DAFB)
CRDO LDA #$0D ;Positive ASCII for <cr>.
(DAFD) JSR OUTDO
(DB5C)
OUTDO ORA #$80 ;Convert to neg ASCII.
CMP #" " ;Is it a ctrl char?
BCC GODOPUT ;Branch if ctrl char.
ORA FLSHMSK ;$40 for FLASH, $00 for INVERSE or NORMAL.
GODOPUT JSR COUT ;Go to the output handling routine.
(DB64)
(FDED)
COUT JMP (CSW)
------------
* DOS's output intercept routine.
(9EBD)
OPUTINCP JSR PREP4DOS
* Prepare for processing by DOS.
(9ED1)
PREP4DOS STA ASAVED ;Save (a), (y) & (x)
STX XSAVED ;registers.
STY YSAVED
TSX ;Adjust stack ptr &
INX ;save it so when we
INX ;later restore it &
(9EDD) STX STKSAVED ;then hit an "RTS"
;we will return to
;the ROUTINE THAT
;CALLED THE ROUTINE
;THAT CONTAINED THE
;"JSR SETUP".
;(In this case, set
;saved stack ptr to
;return to $DB67.)
* Handy entry point frequently
* used by assembly language
* programmers to disconnect
* DOS completely.
(9EE0)
UNCONDOS LDX #3
SETRUHKS LDA CSWTRUE,X ;Restore the I/O
STA CSW,X ;hooks 2 pt 2 the
DEX ;true I/O handlers.
BPL SETRUHKS ;4 bytes to move
(9EEA) RTS ;(0 to 3).
* Use current OPUTCOND value to index table containing
* address of output condition handlers. Do a "stack jump"
* to the appropriate condition handler entry point.
(9EC0) LDA OPUTCOND
ASL ;Times 2 cause 2 bytes/address.
TAX ;Set (x) to index tbl of entry pt addrs.
LDA OUTHNDTB+1,X ;Put adr of output handler on stack
PHA ;(hi byte first) and then do a "stack jump"
LDA OUTHNDTB,X ;to the appropriate entry point.
PHA
LDA ASAVED ;Get char to be printed.
(9ED0) RTS ;Execute the "stack jump".
.
.
STACK JUMP TO OPUTHDL0
.
.
* Output handler 0.
* (Evaluate start of line.)
(9EEB)
OPUTHDL0 LDX RUNTRUPT ;Was a RUN interrupted?
(9EEE) BEQ NONTRUPT ;Branch if not.
* File not being read.
(9EF3)
NONTRUPT LDX CONDNFLG ;Are we doing a warmstart ($00),
;coldstart ($80), using A(RAM) ($C0)
;or doing a READ ($01)?
(9EF6) BEQ SETIGNOR ;Branch if warmstarting.
* Doing a warmstart so set condition 2 as a
* default to signal that non-DOS commands
* should be ignored.
(9F00)
SETIGNOR LDX #2 ;SET CONDITION 2.
STX OPUTCOND
CMP DCTRLCHR ;Is the char = DOS's control character?
(9F08) BNE OPUTHDL2 ;No, it is a <cr> so branch.
* Output handler 2.
* (Ignore non-DOS commands.)
(9F23)
OPUTHDL2 CMP #$8D ;Is char a <rtn>?
BNE DSPLYALL ;Yes - fall thru.
SET2EVAL LDX #0 ;SET CONDITION 0 - evaluate start
STX OPUTCOND ;of line.
(9F2C) JMP DSPLYALL ;Go display char unconditionally.
------------
* Display the char.
(9FA4)
DSPLYALL JSR RESTOREG
* Restore (a), (y) & (x) registers.
(9FBA)
RESTOREG LDA ASAVED
LDY YSAVED
LDX XSAVED
SEC ;Why?????
(9FC4) RTS
(9FA7) JSR GODSPLY
* PRINT A <CR> THROUGH THE TRUE
* OUTPUT HANDLER.
(9FC5)
GODSPLY JMP (CSW)
------------
(FDF0)
COUT1 .
.
(See dis'mbly in APPLE II REFERENCE MANUAL.)
.
.
(RTS)
* Save registers.
(9FAA) STA ASAVED ;Save (a), (y) & (x) registers.
STY YSAVED
(9FB0) STX XSAVED
* Reset hooks & stack pointer.
(9FB3)
DOSEXIT JSR INITIOHK ;Reset DOS hooks.
* Initialize the I/O hooks so that DOS
* intercepts all input & output.
(A851)
INITIOHK .
.
(See dis'mbly above.)
.
.
(RTS)
* Reset stack pointer & save registers.
(9FB6) LDX STKSAVED ;Retrieve the saved stack pointer value
TXS ;& reset the stack to return to caller.
RESTOREG LDA ASAVED ;Restore (a), (y) & (x) registers.
LDY YSAVED
LDX XSAVED
SEC ;Return to routine that called routine
(9FC4) RTS ;that contained "JSR PREP4DOS" instruc.
* Convert char back to positive ASCII
* so we can keep Applesoft happy.
(DB67) AND #$7F ;Convert char.
PHA ;Save it on the stack.
LDA SPEEDFLG ;Delay in accordance with speed setting.
(DB6C) JSR WAIT
* Monitor ROM's main delay routine.
* Delay z number of cycles based on
* the formula:
* z = ((5 * a^2) + (27 * a) + 26) / 2
* where a = value in accumulator on entry.
(FCA8)
WAIT SEC ;Prepare for subtraction.
WAIT2 PHA ;Save (a) on the stack.
WAIT3 SBC #1 ;Keep on reducing (a)
BNE WAIT3 ;until it equals zero.
PLA ;Get original val of (a) off stack.
SBC #1 ;Reduce original (a) down to 0 again.
BNE WAIT2
(FCB3) RTS
(DB6F) PLA ;Get saved positive ASCII char back from stack.
(DB70) RTS
(DB00) EOR #$FF ;No reason for this???
(DB02) RTS
- PRINT THE APPLESOFT PROMPT through
- Basic, DOS's output handler (OPUTINCP)
- and the monitor. THEN, INTERCEPT INPUT
- through DOS's input handler (INPTINCP).
(D43F) LDX #$DD ;RH brackett for Applesoft prompt.
(D441) JSR INLINPL2
(D52E)
INLINPL2 STX PROMPT
(D530) JSR GETLN
* Get a line of input.
(FD6A)
GETLN LDA PROMPT ;Print prompt.
(FD6C) JSR COUT
(FDED)
COUT JMP (CSW) ;Output hook pts to DOS's output handler.
------------
* DOS's output intercept routine.
(9EBD)
OPUTINCP JSR PREP4DOS
(9ED1)
PREP4DOS STA ASAVED ;Save (a), (y) & (x)
STX XSAVED ;registers.
STY YSAVED
TSX ;Adjust stk ptr and
INX ;save it so that
INX ;when we later
(9EDD) STX STKSAVED ;restore it and hit
;an "RTS", we can
;return to routine
;that called the
;routine that
;contained the
;"JSR PREP4DOS"
;instruction.
;(In this case, set
;saved stack ptr to
;return to $FD6F.)
* Restore the I/O hooks to point to the
* true I/O handlers, ex:
* KSWTRUE: KEYIN --> KSW: KEYIN.
* CSWTRUE: COUT1 --> CSW: COUT1.
(9EE0)
UNCONDOS LDX #3
SETRUHKS LDA CSWTRUE,X
STA CSW,X
DEX
BPL SETRUHKS ; 4 bytes to move
(9EEA) RTS ;(0 to 3).
* Use current OPUTCOND value to index table containing
* address of output condition handlers. Do a "stack jump"
* to the appropriate condition handler entry point.
(9EC0) LDA OPUTCOND
ASL ;Times 2 cause 2 bytes/address.
TAX ;Set (x) to index table of addresses.
LDA OUTHNDTB+1,X ;Put adr of output handler on stack
PHA ;(hi byte first) and then do a "stack jump"
LDA OUTHNDTB,X ;to the appropriate entry point.
PHA
LDA ASAVED ;Get char to be printed.
(9ED0) RTS ;Execute the "stack jump".
.
.
STACK JUMP TO OPUTHDL0
.
.
* Output handler 0.
* (Evaluate start of line.)
(9EEB)
OPUTHDL0 LDX RUNTRUPT ;Was a RUN interrupted?
(9EEE) BEQ NONTRUPT ;Branch if not.
* File not being read.
(9EF3)
NONTRUPT LDX CONDNFLG ;Are we doing a warmstart ($00),
;coldstart ($80), using A(RAM) ($C0)
;or doing a read ($01)?
(9EF6) BEQ SETIGNOR ;Branch if warmstarting.
* Warmstarting, so set condition 2.
(9F00)
SETIGNOR LDX #2 ;SET CONDITION 2 as a default to signal
STX OPUTCOND ;that we should ignore non-DOS commands.
CMP DCTRLCHR ;Is char = DOS's ctrl char?
(9F08) BNE OPUTHDL2 ;No, it is a prompt so take branch.
* Output handler 2.
* (Ignore non-DOS commands.)
(9F23)
OPUTHDL2 CMP #$8D ;<rtn>?
(9F25) BNE DSPLYALL ;No, isn't a <cr> so take branch.
* Display the char.
(9FA4)
DSPLYALL JSR RESTOREG
* Restore (a), (y) & (x) registers.
(9FBA)
RESTOREG LDA ASAVED
LDY YSAVED
LDX XSAVED
SEC ;Why?????
(9FC4) RTS
(9FA7) JSR GODSPLY
(9FC5)
GODSPLY JMP (CSW)
------------
* PRINT APPLESOFT PROMPT through
* the true output handler.
(FDF0)
COUT1 .
.
- print char thru true output handler.
(See dis'mbly in APPLE II REFERENCE MANUAL.)
.
.
(RTS)
* Save registers & reset hooks.
(9FAA) STA ASAVED ;Save (a), (y) & (x) registers.
STY YSAVED
(9FB0) STX XSAVED
* Routine to exit DOS.
(9FB3)
DOSEXIT JSR INITIOHK
* Initialize the I/O hooks so that DOS
* intercepts all input & output.
(A851)
INITIOHK .
.
(See dis'mbly given above.)
.
.
(9FC4) (RTS)
(9FB6) LDX STKSAVED ;Retrieve the saved stack pointer val
TXS ;& reset the stack to return to caller.
RESTOREG LDA ASAVED ;Restore (a), (y) & (x) registers.
LDY YSAVED
LDX XSAVED
SEC ;Return to the routine that called the
(9FC4) RTS ;routine that contained the "JSR PREP4DOS"
;instruction.
*******************************
* *
* GET A SINGLE BYTE OF INPUT.
* *
*******************************
(FD6F) LDX #1
BCKSPC TXA ;Force fall thru to next instruction.
BEQ GETLNZ
DEX ;Initialize (x) = 0 as index to input buf.
NXTCHAR JSR RDCHAR
(FD75)
* Routine to read an input byte.
(FD35)
RDCHAR JSR RDKEY
(FD0C)
RDKEY LDY CH ;Get horiz cursor
;pos'n 4 nxt char.
(FD0E) LDA (BASL),Y ;Pick up char in next
(FD10) PHA ;screen pos'n & save
;it on the stack.
(FD11) AND #$3F ;Convert char to
ORA #$40 ;flashing.
(FD15) STA (BASL),Y ;Put flashing char
;on scrn to serve
;as cursor.
(FD17) PLA ;Get char back that
;cursor is replacing.
;(Need it in case do
;bkspc or -> and
;want to reinstate
;orig char on scrn).
(FD18) JMP (KSW) ;Input hook still
------------ ;pointing to DOS.
************** NOTE *******************
* In order to keep things simple, the *
* following disassembly assumes that: *
* 1) we are not EXECing or RUNning a *
* program. *
* 2) no control chars are input from *
* the keyboard. *
***************************************
* DOS intercepts input.
(9E81)
INPTINCP JSR PREP4DOS ;Save regs & stk ptr
* Adjust & save stk
* ptr so can later
* return to $FD38.
* Pt hks at true
* I/O handlers.
(9ED1)
PREP4DOS .
.
(See dis'mbly
above.)
.
.
(RTS)
(9E84) LDA CONDNFLG ;Test condition.
(9E87) BEQ INPUTWRM ;Branch if warmstart.
* Using warmstart condition.
* At this point, both CONDNFLG
* & OPUTCOND = 0 for both
* cold- and warmstarts.
(9E9E)
INPUTWRM LDA EXECFLAG ;Are we execing?
(9EA1) BEQ INPTNOXC ;No
(9EA6)
INPTNOXC LDA #3 ;SET CONDITION 3 to
(9EA8) STA OPUTCOND ;to signal that we
;want to process
;input information.
(9EAB) JSR RESTOREG
* Restore regs.
(9FBA)
RESTOREG LDA ASAVED
LDY YSAVED
LDX XSAVED
SEC
(9FC4) RTS
(9EAE) JSR TOTRUIN
* Go to the true
* input handler.
(9EBA)
TOTRUIN JMP (KSW)
------------
************** N O T E ***************
* * * Increment the
* You are here when DOS is up, you're * * random # locs
* not running a program & THE COMPUTER * * & get code of
* IS BLINKING AT YOU WHILE WAITING FOR * * the key pressed.
* INPUT FROM THE KEYBOARD -----------------------------------------------------------------------> (FD1D)
* * KEYIN INC RNDL
**************************************** BNE KEYIN2
INC RNDH
KEYIN2 BIT KBD
BPL KEYIN
STA (BASL),Y
LDA KBD
BIT KBDSTRB
(FD2E) RTS
(9EB1) STA ASAVED ;SAVE CHAR JUST READ.
(9EB4) STX XSAVED ;SAVE INDEX TO INPUT
;BUFFER.
(9EB7) JMP DOSEXIT
------------
* Routine to exit DOS.
(9FB3)
DOSEXIT JSR INITIOHK
* Initialize I/O hks
* so DOS intercepts
* all input & output.
(A851)
INITIOHK .
.
(See dis'mbly above.)
.
.
(RTS)
(9FB6) LDX STKSAVED ;Restore stk pointer.
TXS
RESTOREG LDA ASAVED ;Restore registers.
LDY YSAVED
LDX XSAVED
SEC ;Why?????
(9FC4) RTS ;RETURN TO THE ROUTINE
;THAT CALLED THE
;ROUTINE THAT
;CONTAINED THE
;"JSR PREP4DOS"
;INSTRUCTION.
(FD38) CMP #$9B ;Was the escape key pressed?
BEQ ESC ;Yes - go handle escape.
(FD3C) RTS
(FD78) CMP #$95 ;Was char a ctrl-U (right arrow)?
BNE CAPTST ;No.
(FD7C) LDA (BASL),Y ;Yes - prepare to put the original image
; of char in the next screen pos'n
(FD7E) ; back on the screen.
CAPTST CMP #$E0 ;Was char lower case?
BCC ADDINP ;No - go put new char in the input buffer.
AND #$DF ;Convert lower case to upper case.
ADDINP STA BUFF200,X ;Put char in the input buffer.
CMP #$8D ;Was char input a <cr>?
(FD89) BNE NOTCR ;Branch if char wasn't a <cr>.
* A <cr> was typed in from the keyboard
* denoting the end of input.
(FD8B) JSR CLREOL
* Clear to end of line.
(FC9C)
CLREOL LDY CH ;(y) = next char's screen position.
CLEOLZ LDA #" " ;(a) = space to blank out line.
CLEOL2 STA (BASL),Y ;Put blanks on screen from the next
INY ;char position to the end of the screen
CPY WNDWDTH ;line (as determined by WNDWDTH).
BCC CLEOL2
(FCA7) RTS
(FD8E)
CROUT LDA #$8D ;Set (a) = carriage return.
(FD90) BNE COUT ;ALWAYS.
(FDED)
COUT JMP (CSW)
------------
* DOS's output intercept routine.
(9EBD)
OPUTINCP JSR PREP4DOS
* Prepare for processing by DOS.
*
* Save the registers & stack pointer.
* Restore the I/O hooks to point to the
* true I/O handlers, ex:
* KSWTRUE: KEYIN --> KSW: KEYIN.
* CSWTRUE: COUT1 --> CSW: COUT1.
(9ED1)
PREP4DOS STA ASAVED ;Save (a), (y) & (x) registers.
STX XSAVED
STY YSAVED
TSX ;Adjust stack ptr & save it so when we
INX ;later restore it & then hit an "RTS"
INX ;instruction, we will return to the
(9EDD) STX STKSAVED ;ROUTINE THAT CALLED THE ROUTINE THAT
;CONTAINED THE "JSR SETUP" INSTRUCTION.
;(In this case, set saved stack pointer
;so we can return to $D533.)
* Handy entry point frequently used by
* assembly language programmers to disconnect
* DOS completely.
(9EE0)
UNCONDOS LDX #3
SETRUHKS LDA CSWTRUE,X ;Restore the I/O hooks to point
STA CSW,X ;to the true I/O handlers.
DEX
BPL SETRUHKS ;4 bytes to move (0 to 3).
(9EEA) RTS
* Use current OPUTCOND value to index table containing
* address of output condition handlers. Do a "stack jump"
* to the appropriate condition handler entry point.
(9EC0) LDA OPUTCOND
ASL ;Times 2 cause 2 bytes/address.
TAX ;Set (x) to index tbl of entry pt addrs.
LDA OUTHNDTB+1,X ;Put adr of output handler on stack
PHA ;(hi byte first) and then do a "stack jump"
LDA OUTHNDTB,X ;to the appropriate entry point.
PHA
LDA ASAVED ;Get char to be printed.
(9ED0) RTS ;Execute the "stack jump".
.
.
STACK JUMP TO OPUTHDL3
.
.
* Output handler 3.
* (PROCESS THE INPUT INFORMATION.)
(9F2F)
OPUTHDL3 LDX #0 ;SET CONDITION 0 when input ends.
STX OPUTCOND
CMP #$8D ;Was char an input-terminating <cr>?
(9F36) BEQ ASUMIMED ;Yes.
(9F3F)
ASUMIMED PHA ;Save character on the stack.
(9F40) SEC ;(c) = 1, default condition to assume we
;are presently in the immediate mode.
(9F41) LDA EXECFLAG ;Check if we are EXECing.
BNE TESTMODE ;Branch if we are EXECing.
(9F46) JSR CKBSCRUN ;Not execing so see if basic is running a
;program or not.
* Check if basic is running a program.
(A65E)
CKBSCRUN PHA ;Save (a) on the stack.
LDA ACTBSFLG ;Check which basic is up.
(A662) BEQ INTBASIC ;Branch if using integer.
* Using Applesoft, so now check the hi byte
* of the line number to see if in immediate
* mode or not. If line number > 65288 (ie. $FF
* in hi byte) then we are in the immediate mode.
(A664) LDX CURLIN+1 ;Check hi byte of the line number.
INX ;If $FF --> $00, then number > 65288.
(A667) BEQ IMEDMODE ;Branch if using immediate mode.
* FP appears to be running a program but,
* maybe CURLIN+1 was zapped, so better
* also check the prompt.
(A669) LDX PROMPT
CPX #$DD ;Applesoft prompt (RH brackett)?
BEQ IMEDMODE ;Yes - so must be in the immediate mode.
RUNNING PLA ;Get the saved (a) back from the stack.
CLC ;Signal that the program is running.
(A671) RTS
============
(A672)
INTBASIC LDA RUNMODE ;Check Integer basic's run mode flag.
(A674) BMI RUNNING ;If negative, then Integer basic is in
(A676) ;the deferred mode.
IMEDMODE PLA ;Get saved (a) back from the stack.
SEC ;Signal that we are in the immediate mode.
(A678) RTS
============
(9F49)
TESTMODE PLA ;Retrieve char from the stack.
(9F4A) BCC TESTEXEC ;Branch if basic is running.
;(c) = 0 = either basic running.
;(c) = 1 = immediate mode.
* Execing or in immediate mode.
(9F4C) LDX XSAVED ;Retrieve index to the input buffer.
(9F4F) JMP PUTINBUF ;Go put char in input buf (condition 1).
------------
* Put char in the input buffer & then
* go display char or else go parse the
* command.
(9F15)
PUTINBUF STA BUF200,X ;Put char in the input buffer.
INX ;Kick up index to the next buffer pos'n.
STX NDX2INBF
CMP #$8D ;Was char a carriage return?
BNE DSPLYCMD ;No.
(9F20) JMP PARSECMD ;Yes - got end of input, so now go
------------ ; and see if it is a DOS command.
* Input character was not a carriage return.
(FD3D)
NOTCR LDA INVFLG ;Save current inverse flag on stack.
PHA
LDA #$FF ;Set inverse flag to normal.
STA INVFLG
LDA BUF200,X ;Get char to be printed.
(FD47) JSR COUT
(FDED)
COUT JMP (CSW) ;Output hook pts to DOS's output handler.
------------
* DOS's output intercept routine.
(9EBD)
OPUTINCP JSR PREP4DOS
(9ED1)
PREP4DOS STA ASAVED ;Save (a), (y) & (x)
STX XSAVED ;registers.
STY YSAVED
TSX ;Adjust stk ptr and
INX ;save it so that
INX ;when we later
(9EDD) STX STKSAVED ;restore it and hit
;an "RTS", we can
;return to $FD4A.
* Restore the I/O hooks to point to the
* true I/O handlers, ex:
* KSWTRUE: KEYIN --> KSW: KEYIN.
* CSWTRUE: COUT1 --> CSW: COUT1.
(9EE0)
UNCONDOS LDX #3
SETRUHKS LDA CSWTRUE,X
STA CSW,X
DEX
BPL SETRUHKS ; 4 bytes to move
(9EEA) RTS ;(0 to 3).
* Use current OPUTCOND value to index table containing
* address of output condition handlers. Do a "stack jump"
* to the appropriate condition handler entry point.
(9EC0) LDA OPUTCOND
ASL ;Times 2 cause 2 bytes/address.
TAX ;Set (x) to index table of addresses.
LDA OUTHNDTB+1,X ;Put adr of output handler on stack
PHA ;(hi byte first) and then do a "stack jump"
LDA OUTHNDTB,X ;to the appropriate entry point.
PHA
LDA ASAVED ;Get char to be printed.
(9ED0) RTS ;Execute the "stack jump".
.
.
STACK JUMP TO OPUTHDL3
.
.
* Output handler 3.
* (Process the input information.)
(9F2F)
OPUTHDL3 LDX #0 ;SET CONDITION 0 when input ends.
STX OPUTCOND
CMP #$8D ;Carriage return?
(9F36) BEQ ASUMIMED ;Yes.
* Char was not a carriage return.
(9F38)
TESTEXEC LDA EXECFLAG ;Are we EXECing?
(9F3B) BEQ DSPLYALL ;No.
* Display the char.
(9FA4)
DSPLYALL JSR RESTOREG
* Restore (a), (y) & (x) registers.
(9FBA)
RESTOREG LDA ASAVED
LDY YSAVED
LDX XSAVED
SEC ;Why?????
(9FC4) RTS
(9FA7) JSR GODSPLY
(9FC5)
GODSPLY JMP (CSW)
------------
* PRINT INPUT CHAR THROUGH
* THE TRUE OUTPUT HANDLER.
(FDF0)
COUT1 .
.
(See dis'mbly in APPLE II REFERENCE MANUAL.)
.
.
(RTS)
* Save registers & reset hooks.
(9FAA) STA ASAVED ;Save (a), (y) & (x) registers.
STY YSAVED
(9FB0) STX XSAVED
* Routine to exit DOS.
(9FB3)
DOSEXIT JSR INITIOHK
* Initialize the I/O hooks so that DOS
* intercepts all input & output.
(A851)
INITIOHK .
.
(See dis'mbly given above.)
.
.
(RTS)
(9FB6) LDX STKSAVED ;Retrieve the saved stack pointer val
TXS ;& reset the stack to return to caller.
RESTOREG LDA ASAVED ;Restore (a), (y) & (x) registers.
LDY YSAVED
LDX XSAVED
SEC ;Return to the routine that called the
(9FC4) RTS ;routine that contained the "JSR PREP4DOS"
;instruction.
(FD4A) PLA ;Restore the original contents of the
STA INVFLG ;inverse flag.
LDA BUF200,X ;(a) = char that was input.
CMP #$88 ;Was char a backspace?
BEQ BCKSPC ;Yes.
CMP #$98 ;Was char a ctrl-X (cancel char)?
BEQ CANCEL ;Yes.
CPX #$F8 ;Input 249 (0 to 248) chars yet?
BCC NOTCR1 ;No.
JSR BELL ;Yes - go ring the warning bell.
NOTCR1 INX ;Increase the input character counter.
(FD60) BNE NXTCHAR ;Character counter hasn't wrapped around to
(FD62) ;zero yet, so go get next char.
CANCEL . ;Too many chars were input, so go cancel
. ;the input line.
.
============
(9FCD)
PARSECMD .
.
************************************
* - PARSE & EXECUTE THE COMMAND. *
* - Enter with STKSAVED set to *
* return to $D533. *
* - Return with I/O hooks pointing *
* to DOS's input/output handling *
* routines. *
* - Note: The computer ends up in *
* an infinite loop if a BRUN cmd *
* was just executed AND if the *
* binary file performed any *
* output or input OR if the prgm *
* returns with MON C in effect. *
* (See dis'mbly of the BRUN cmd *
* handler for details.) *
************************************
.
.
- See disassembly titled "DOSCMDPARSING&PROCESSING".
.
.
(RTS)
(D533) CPX #$EF ;240 characters yet (0 to 23)?
BCC TERMIN8 ;No.
LDX #$EF ;Yes.
TERMIN8 LDA #0 ;Put an end-of-line marker (EOL, $00)
STA BUF200,X ;in the input buffer.
TXA ;Is (x) = 0?
(D53F) BEQ NEG8NPUT ;Yes - so just completed a SIMPLE IMMEDIATE
; MODE DOS COMMAND & have set the first
; byte in the input buffer to a $00.
* No simple immediate mode DOS command present,
* so if the line contains any DOS commands, they
* must be in a PRINT program statement or in an
* immediate mode PRINT statement.
* for example: 100 D$ = CHR$(4): PRINT D$;"CATALOG"
* OR
* D$ = CHR$(4): PRINT D$;"CATALOG"
* In either case, we are dealing with an Applesoft
* statement, so strip the hi bit off the characters
* (ie. convert to positive ASCII to keep Applesoft
* happy).
(D541)
CNVRTPOS LDA BUF200-1,X ;Get the byte in the input buffer.
AND #$7F ;Strip off the hi bit.
(D546) STA BUF200-1,X ;Put the positive ASCII char back in
;the input buffer.
(D549) DEX ;Reduce the index to the input buffer.
BNE CNVRTPOS ;When (x) = 0, done stripping.
NEG8NPUT LDA #0 ;Initialize (a) = 0.
LDX #<BUF200-1 ;Set (x) = $FF.
LDY #>BUF200-1 ;Set (y) = $01.
(D552) RTS
(D444) STX TXTPTR ;Set TXTPTR to point 1 byte below the
STY TXTPTR+1 ;input buf (ie. $1FF) - will increment it later.
LSR ERRFLG ;Zero out the error flag.
(D44A) JSR CHRGET ;Get the first byte in the input buffer.
* Get a byte from the input buffer.
* Note: Uses SELF-MODIFYING code.
* On exit: (a) = char from input buf.
* (z) = 1 only if ':' (end-of-statement marker, EOS,
* $3A) or $00 (end-of-line maker, EOL).
* = 0 for all other values.
* (c) = 0 only if ASCII number betw'n '0' <----> '9',
* (ie, $30 ,----> $39).
* = 1 for all other values.
(00B1)
CHRGET INC TXTPTR ;Modify pointer to input buffer.
BNE CHRGOT
(00B5) INC TXTPTR+1
(00B7)
CHRGOT HEX AD ;Actually an absolute "LDA" opcode.
TXTPTR DS 2 ;Contents modified by INC instructions above.
(00B8) ;The above three bytes are therefore equivalent
;to the non-existent instruction: LDA (TXTPTR)
;which assumes a zero index. (PS. By using self-
;modifying code, we do the equivalent of an indirect
;load without having to mess up the y-register.)
(00BA) CMP ':' ;Is char an EOS ($3A) or greater?
BCS CHRGTRTN ;Yes
CMP ' ' ;Space?
(00C0) BEQ CHRGET ;Yes - ignore spaces.
* Play with (a) and exit with (a) intact
* but (c) and (z) conditioned.
* Do: (a) - $30 - $D0. That is, do the
* equivalent to:
* (a) - $30 + $30 or (a) + $D0 - $D0,
* because $30 = two's complement of $D0
* and $D0 = two's complement of $30.
(00C2) SEC ;Prep for dummy subtraction.
SBC '0' ;That is: (a) = (a) - $30 or (a) = (a) + $D0
(00C5) SEC ;Prep for next dummy subtraction (which will
;reinstate (a) to its original value).
(00C6) SBC #$D0 ;That is: (a) = (a) - $D0 or (a) = (a) + $30
;Reinstates (a) to original entry value but
;conditions (c) and (z).
CHRGTRTN RTS ;Exit with (a) = orig char.
(00C8) ; (z) = 0 if EOS (':', $3A)
; or EOL ($00).
; (c) = 0 if '0' <----> '9'
; ($30 <----> $39).
(D44D) TAX ;Stick it in (x)
(D44E) BEQ RESTART ;IF THE FIRST BYTE IS A $00, THEN WE HAVE
;JUST COMPLETED A SIMPLE IMMEDIATE MODE DOS
;COMMAND, SO NOW GO BACK TO GET THE NEXT
;LINE OF INPUT.
- Did not just complete a simple immediate mode
- DOS command. Therefore, if any DOS commands
- are indeed present, they must be imbedded in
- an Appplesoft program or else in an immediate
- mode line.
.
.
- set the immediate mode.
- if the first character in the input buffer is
a number, then we must be adding a program line
so go to the appropriate Applesoft routine.
- if the first character is not a number, then go
to Applesoft's parse routine and parse the line
(ie. tokenize it).
- after tokenization, check if the trace flag is on
and then go execute each statement in the line.
- when a statement requiring input or output is
encountered, DOS regains control via the I/O
hooks.
- eventually, we end up back at the RESTART ($D43C)
routine waiting for input.