C02/x16/include/vera.a02

; C02 module vera.h02 assembly language subroutines

;getmod() - Get Layer 0/1 Mode
;Args: A = Layer (0/1)
;Affects: Y
;Returns: A = Layer Mode
;         X = Current Data Port
GETMOD: JSR GETLRC  ;Read Register
        LSR         ;Shift Left Five Bits
        LSR         
        LSR
        LSR
        RTS

;getenb() - Get Layer 0/1 Enabled
;Args: A = Layer (0/1)
;Affects: Y
;Returns: A = $FF - Layer Enabled
;             $00 - Layer Disabled
;         X = Current Data Port
GETENB: JSR GETLRC  ;Read Register
        AND #$01    ;Isolate Bit 1
        BEQ GETENX  ;If Set 
        LDA #$FF    ;  Return TRUE
GETENX: RTS         ;Else Return FALSE        

;getlrc() - Get Layer 0/1 Control Register
;Args: A = Layer (0/1)
;Affects: Y
;Returns: A = Control Register Contents
;         X = Current Data Port
GETLRC: LDX #0      ;Set Offset to Control Register

;getlrr() - Get Layer 0/1 Register
;Args: A = Layer (0/1)
;      X = Register Offset
;Affects: Y
;Returns: A = Contents of Register
;         X = Current Data Port
GETLRR: JSR GETLRP  ;Get Layer Page in Y
        JMP GETREG  ;and Read Register Contents

;getlrp() - Get Layer 0/1 Register Page
;Args: A = Layer (0/1)
;Returns: A,Y = Layer Register Page
GETLRP: AND #$01    ;Isolate Bit 1
        ASL         ;Move to Left Nybble
        ASL
        ASL
        ASL
        ORA #$20    ;And Add to 2
        TAY         ;Return Page in Y
        RTS

;getchd(index, &array) - Read Character Data into Array
;Args: A = Character Index
;      Y,X = Address of Array to Read into
;Destroys: TEMP0,TEMP1,TEMP2
;Returns: A = Number of Bytes Read
GETCHD: JSR SETDST      ;Store Address in Destination Pointer
        STA TEMP1       ;Set Offset LSB to Index
        LDA #0          ;Set Offset MSB to Zero
        ASL TEMP1       ;Multiple Offset by 2
        ROL             
        STA TEMP2       ;and Store MSB
        JSR GETLRI      ;Get Tile Base
        TXA             ;Add Offset To Tile Base
        CLC
        ADC TEMP0
        STA TEMP0
        TYA
        ADC TEMP1
        STA TEMP1
        LDA #0
        ADC #0
        JSR GETMBX      ;Multiply by 4
        ORA #$10        ;Set Auto-Increment to 1
        JSR SETADR      ;and Set Vera Address
        LDA #8          ;Set Byte Count to 8
        JMP GETMEA      ;and Read Bytes into Array

;gettba() - Get Layer 0/1 Tile Base Address
;Args: A = Layer (0/1)
;Destroys: TEMP1,TEMP2
;Returns: A = Tile Base Bank
;         Y,X = Tile Base Address
GETTBA: LDX #4      ;Set Register Offset
        .DC $2C     ;Read Register Pair and Rotate

;getmba() - Get Layer 0/1 Map Base Address
;Args: A = Layer (0/1)
;Destroys: TEMP1,TEMP2
;Returns: A = Map Base Bank
;         Y,X = Map Base Address
GETMBA: LDX #2      ;Set Register Offset
        JSR GETLRI  ;Read Register Pair as Integer
        LDA #0      ;Initialize Page to 0
        JSR SAVRXY  ;Save Integer in TEMP1,TEMP2
GETMBX: LDX #2      ;Do Twice
GETMBL: ASL TEMP1   ;  Rotate LSB
        ROL TEMP2   ;  MSB and
        ROL         ;  Bank Left
        DEX
        BNE GETMBL
        JMP RESRXY  ;Load LSB, MSB and Return

;getvsc() - Get Layer 0/1 Vertical Scroll
;Args: A = Layer (0/1)
;Returns: A,X = Vertical Scroll LSB
;         Y = Vertical Scroll MSB
GETVSC: LDX #8      ;Set Register Offset
        .DC $2C     ;Skip to GETLRI (BIT Absolute)

;gethsc() - Get Layer 0/1 Horizontal Scroll
;Args: A = Layer (0/1)
;Returns: A,X = Horizontal Scroll LSB
;         Y = Horizontal Scroll MSB
GETHSC: LDX #6      ;Set Register Offset
        .DC $2C     ;Skip to GETLRI (BIT Absolute)

;gettbs() - Get Layer 0/1 Tile Base
;Args: A = Layer (0/1)
;Returns: A,X = Tile Base LSB
;         Y = Tile Base MSB
GETTBS: LDX #4      ;Set Register Offset
        .DC $2C     ;Skip to GETLRI (BIT Absolute)

;getmbs() - Get Layer 0/1 Map Base
;Args: A = Layer (0/1)
;Returns: A,X = Map Base LSB
;         Y = Map Base MSB
GETMBS: LDX #2      ;Set Register Offset

;getlri() - Get Layer 0/1 Register Pair as Integer
;Args: A = Layer (0/1)
;      X = Register Offset
;Returns: A,X = Integer LSB
;         Y = Integer LSB
GETLRI: JSR GETLRP  ;Get Layer Page in Y
        JMP GETREI  ;and Read Register Contents

;mapsiz() - Convert Map Size Specifier to Pixels
;Args: A = Map Size Specifier
;Affects: A
;Returns: Y,X Map Size in Pixels
MAPSIZ: TAX             ;Copy Map Size Specifier to X
        LDA MAPSIH,X    ;Load Pixels MSB from Table
        TAY             ;and Return in Y
        LDA MAPSIL,X    ;Load Pixels LSB from Table
        TAX             ;and Return in X
MAPSIL: .DC $20,$40,$80,$00
MAPSIH: .DC $00,$00,$00,$01
        
;tilsiz() - Convert Tile Size Specifier to Pixels
;Args: A = Tile Size Specifier
;Affects: A
;Returns: A Tile Size in Pixels
TILSIZ: TAX             ;Copy Map Size Specifier to X
        LDA TILSIT,X    ;Load Pixels MSB from Table
        RTS
TILSIT: .DC $08,$10

;gettsz() - Get Layer 0/1 Tile Size

;getmsz() - Get Layer 0/1 Map Size
;Args: A = Layer (0/1)
;Affects: X
;Returns: A = Map Width Specifier
;         Y = Map Height Specifier

;settbs() - Set Layer 0/1 Map Base
;Args: A = Layer (0/1)
;      Y,X = Map Base
;Sets: TEMP1,TEMP2 = Map Base
;Affecta: A,Y,X
SETTBS: JSR SAVRXY  ;Store Map Base in TEMP1,TEMP2
        LDX #4      ;Set Register Offset
        BNE SETLRI  ;Write to Layer Register
        
;setmbs() - Set Layer 0/1 Map Base
;Args: A = Layer (0/1)
;      Y,X = Map Base
;Sets: TEMP1,TEMP2 = Map Base
;Affecta: A,Y,X
SETMBS: JSR SAVRXY  ;Store Map Base in TEMP1,TEMP2
        LDX #2      ;Set Register Offset
        BNE SETLRI  ;Write to Layer Register

;setvsc() - Set Layer 0/1 Vertical Scroll
;Args: A = Layer (0/1)
;      Y,X = Map Base
;Sets: TEMP1,TEMP2 = Vertical Scroll
;Affecta: A,Y,X
SETVSC: JSR SAVRXY  ;Store Vertical Scroll in TEMP1,TEMP2
        LDX #8      ;Set Register Offset
        BNE SETLRI  ;Write to Layer Register

;sethsc() - Set Layer 0/1 Horizontal Scroll
;Args: A = Layer (0/1)
;      Y,X = Map Base
;Sets: TEMP1,TEMP2 = Horizontal Scroll
;Affecta: A,Y,X
SETHSC: JSR SAVRXY  ;Store Horizontal Scroll in TEMP1,TEMP2
        LDX #6      ;Set Register Offset

;setlri() - Write Integer to Get Layer 0/1 Register
;Args: A = Layer (0/1)
;      X = Register Offset
;Uses: TEMP1,TEMP2 = Integer Value
;Affecta: A,Y,X
SETLRI: JSR GETLRP  ;Get Layer Page in Y
        JMP SETREI  ;and Write Integer to Register