; C02 Program Initialization Code for BBC Micro

;System Specific ASCII Key Mappings
DELKEY  EQU $7F     ;Delete/Backspace Key ($08=Backspace, $7F=Delete)
ESCKEY  EQU $1B     ;Escape/Stop Key      ($03=Ctrl-C, $1B=Escape)
RTNKEY  EQU $0D     ;Return/Enter Key     ($0D=Carriage Return)
NULKEY  EQU $00     ;No Key was Pressed   ($00=Null)

;Zero Page Locations
SRCPTR  EQU $70     ;Source Pointer
DSTPTR  EQU $72     ;Destination String Pointer (string.asm)
BFRLO   EQU $74     ;Buffer Pointer LSB [Temporary String Pointer]
BFRHI   EQU $75     ;Buffer Pointer MSB [Temporary String Pointer]
BLKPTR  EQU $76     ;Block Pointer
STKLO   EQU $78     ;Stack Pointer
STKHI   EQU $79     ;  Unused by OS

TEMP0   EQU $80     ;Temporary Storage
TEMP1   EQU $81
TEMP2   EQU $82
TEMP3   EQU $83

BLKBGN  EQU $84     ;Block Start Address
BLKEND  EQU $86     ;Block End Address

STKSLO  EQU $88     ;Stack Start Address
STKSHI  EQU $89
STKELO  EQU $8A     ;Stack End Address
STKEHI  EQU $8B

;       EQU $8C     ;Unused
;       EQU $8D     ;Unused
;       EQU $8E     ;Unused
RANDOM  EQU $8F     ;Pseudo-RANDOM Number Storage
RDSEED  EQU $0296   ;System Clock Low Byte

        ORG $1900   ;Program Start Address

START:  JMP MAIN    ;Execute Program

;Exit Program and Return to Operating System or Monitor
EXIT:   JMP ($FFFC) ;Execute Warm Start

;Poll Character from Keyboard
PLKEY:  LDA #$81    ;Set Command to Read Key
        LDY #0      ;Set Time Limit to 0
        LDX #0
        JSR #FFF4   ;Call OSBYTE
        TYA         ;Check Status Code
        BNE GETCHE  ;If Error, Check for Escape
        TXA         ;Else Return Character
        RTS

;Read Character from Console
GETKEY;             ;Usually Drops into RDKEY, but may need to call RDKEY
                    ;  then clean/convert returned value (e.g. Apple-1) 

;Wait for Character from Keyboard
GETCHR: JSR $FFE0   ;Call System Routine OSRDCH
        BCC GETCHX  ;If Error
GETCHE: CMP #$1B    ;
        BNE GETCHZ  ;  If Escape Pressed
        LDA #$7E    ;    Acknowledge It
        JSR $FFF4   ;    with OSBYTE Call
        LDA #$1B    ;    and Return ESC
        BNE GETCHX  ;  Else 
GETCHZ: LDA #0      ;    Return 0
GETCHX: RTS         

;Delete Previous Character
DELCHR: LDA #$7F    ;Print DEL Character
        JMP PUTCHR

;Advance Cursor to Next line
NEWLIN  EQU $FFE7   ;Aliased to System Routine OSNEWL

;Print Character to Screen
PUTCHR: EQU $FFE3   ;Aliased to OSASCI System Routine

;Clear the Screen
CLRSCR: LDA #$0C    ;Print FF Character
        JMP PUTCHR

;Move Cursor to Specified Coordinates
SETPOS: TAX         ;Save Column in X
        LDA #$1F    ;Issue Move Cursor Command
        JSR PUTCHR
        TXA         ;Send X Coordinate
        JSR PUTCHR
        TYA         ;Send Y Coordinate
        JMP PUTCHR

;Get Cursor Position
GETPOS: LDA $0318   ;Load Text Cursor X Coordinate
        LDY #0319   ;Load Text Cursor Y Coordinate
        RTS

;Get Screen Size
GETSIZ: LDA $030A   ;Get Right Side of Text Window
        SEC
        SBC $0308   ;Subtract Left Side of Text Window
        TAX         ;Copy to X Register
        INX         ;and Add 1
        LDA $0309   ;Get Bottom of Text Window
        SEC
        SBC $030B   ;Subtract Top of Text Window
        TAY         ;Copy to Y Register
        INY         ;and Add 1
        TXA         ;Copy Width to Accumulator
        RTS         ;Return Screen Width in A, Height in Y

        INCLUDE "../include/prbyte.a02" ;PRBYTE and PRHEX routine
        INCLUDE "../include/putstr.a02" ;PUTSTR routine