; C02 library memio.h02 assembly language subroutines
; Requires external routines SETDST, SETSRC
; zero page locations DSTLO, DSTHI, SRCLO and SRCHI
; location TEMP0
; and constant RTNKEY

;char maddr(mp) - Return Contents of Memory Pointer
;Args: A = Zero Page Memory Pointer
;Affects: N,Z reflect Y register
;Returns: A = Memory Pointer LSB
;         Y = Memory Pointer MSB
;         X = Zero Page Memory Pointet Address
MADDR:  TAX             ;Copy Pointer Address to X Register
        LDA 0,X         ;Load Pointer LSB into Accumulator
        LDY 1,X         ;Load Pointer MSB into Y Register
        RTS

;char mopen(mp, &a) - Open Memory File: Set Memory Pointer to specified Address
;Args: A = Zero Page Memory Pointer
;      X,Y = Address
;Sets: TEMP0 = Memory Pointer Address
;Affects: N,Z reflect Accumulator
;Returns: A = Zero Page Memory Pointer, otherwise
;             0 if Error Illegal Address (within Zero Page)
MOPEN:  STX TEMP0       ;Save Address LSB
        TAX             ;Copy Memory Pointer to X register
        LDA TEMP0       ;Retrieve Address LSB
        STA 0,X         ;Store in Memory Pointer LSB
        STY 1,X         ;Store Address MSB in Memory Pointer MSB
        LDA 1,X         ;Load Address MSB into Accumulator (Setting Flags)
        BEQ MERROX      ;If 0, Return as Result (Failure)
        TXA             ;Else
        RTS             ;  Return Memory Pointer as Result

;char meof(mp) - Check for End of Memory File
;Args: A = Zero Page Memory Pointer
;Affects: N,Z reflect Accumulator 
;Returns: A,Y = 255 if at End of File or invalid Memory Pointer
;               0 otherwise
;         X = Zero Page Memory Pointer
MEOF:   JSR MERROR      ;Check Memory Pointer
        BNE MCLOSX      ;If Error, Return Else Y will contain 0
        LDA (0,X)       ;If NUL Character at Memory Pointer
        BEQ MERROY      ;  Return 255
        BNE MERROX      ;Else Return 0
        

;char merror(mp) - Check for Memory File Error
;Args: A = Zero Page Memory Pointer
;Affects: N,Z reflect Accumulator 
;Returns: A,Y = 255 if Memory Pointer contains Zero Page Address
;               0 if no error
;         X = Zero Page Memory Pointer
MERRON: STY TEMP1       ;Alternate Entry Point - Save Byte Argument
MERROM: STA TEMP0       ;Alternate Entry Point - Save Memory Pointer
MERROR: TAX             ;Copy Memory Pointer to X register
MERROA: LDY #0          ;Set Error Indicator to 0
        LDA 1,X         ;Load Memory Address High Byte
        BEQ MERROY      ;If 0 
        CMP #255        ;   or
        BNE MERROX      ;   255 
MERROY: DEY             ;  Change Error Indicator to 255
MERROX: TYA             ;Copy Error Indicator to Accumulator
        RTS

;char mclose(mp) - Close Memory File: Write EOF and Clear Memory Pointer
;Args: A = Zero Page Memory Pointer
;Affects: N,Z reflect Accumulator
;Returns: A,Y = 255 if Memory Pointer contains Zero Page Address
;               0 if no error
;         X = Zero Page Memory Pointer
MCLOSE: JSR MFLUSH      ;Check Memory Pointer
        BNE MCLOSX      ;If No Error
        STA 0,X         ;  Write to Addess LSB
        STA 1,X         ;  Write to Addess LSB
MCLOSX: RTS

;char mflush(mp) - Flush Memory File: Write NUL at Memory Pointer
;Args: A = Zero Page Memory Pointer
;Affects: N,Z reflect Accumulator
;Returns: A,Y = 255 if Memory Pointer contains Zero Page Address
;               0 if no error
;         X = Zero Page Memory Pointer
MFLUSH: JSR MERROR      ;Check Memory Pointer
        BNE MCLOSX      ;If No Error
        STA (0,X)       ;  to Current Memory Location
MFLUSX: RTS

;char mgetc(mp) - Read Character from Memory File
;Args: A = Zero Page Memory Pointer
;Affects: N,Z reflect Accumulator
;Returns: A = Character read from memory
;         Y = 255 if Error or EOF
;             0 if no error
;         X = Zero Page Memory Pointer
MGETC:  JSR MERROR      ;Check Memory Pointer
        BNE MGETCX      ;If No Error 
        LDA (0,X)       ;  Load Character at Memory Location
MGETCI: PHP             ;  Save Flags
        INC 0,X         ;  Increment Memory Pointer Low Byte
        BNE MGETCP      ;  If 0
        INC 1,X         ;    Increment Memory Pointer High Byte
MGETCP: PLP             ;  Restore Flags
MGETCX: RTS

;char mputc(mp, c) - Write Character to Memory File
;Args: A = Zero Page Memory Pointer
;      Y = Character to Write to Memory
;Sets: TEMP0 = Character to Write
;Affects: N,Z reflect Accumulator
;Returns: A,Y = 255 if invalid Memory Pointer
;               0 if no error
;         X = Zero Page Memory Pointer
MPUTC:  JSR MERRON      ;Save Argumebts & Check Memory Pointer
        BNE MGETCX      ;If Error, then Return 
        LDA TEMP1       ;Retrieve Character to Write
        STA (0,X)       ;Store in Memory
        LDA #0          ;Clear Accumulator, Z and N flags
        BEQ MGETCI      ;and Increment Memory Pointer

;char mgets(mp, &s) - Read from Memory File into String
;Args: A = Zero Page Memory Pointer
;      Y,X = Address of String to Read into
;Sets: TEMP0 = Memory Pointer
;      TEMP1 = Number of characters read
;Affects: N,Z reflect Accumulator
;Returns: A = 255 if invalid Memory Pointer
;             otherwise length of string read
;         Y = Last character in string
;         X = Zero Page Memory Pointer
MGETS:  JSR SETDST      ;Set String Address as Destination
        JSR MERROM      ;Save Memory Pointer & Check Memory Pointer
        BNE MGETCX      ;If Error then Return, Else Y will be 0
        LDA 0,X         ;Copy Memory Pointer LSB 
        STA SRCLO       ;to Source Pointer LSB
        LDA 1,X         ;Copy Memory Pointer MSB
        STA SRCHI       ;to Source Pointer MSB
MGETSL: LDA (SRCLO),Y   ;Get Character from Memory
        BEQ MGETSX      ;If Not NUL (End of File)
        CMP #32         ;  Check for Control Character
MGETSS: STA (DSTLO),Y   ;  Store Character in String
        INY             ;  increment offset and
        BCC MGETSX      ;  If Not Control character
        BPL MGETSL      ;    loop if less than 128
MGETSX: TAX             ;Copy Final Character to X
        LDA #$00        ;Terminate String        
        STA (DSTLO),Y   ;        
        BEQ MPUTSX      ;Update Memory Pointer and Return String Length

;char mputs(mp, &s) - Write String to Memory File
;Args: A = Zero Page Memory Pointer
;      Y,X = Address of String to Read into
;Sets: TEMP0 = Memory Pointer
;      TEMP1 = Number of characters written
;Affects: N,Z reflect Accumulator
;Returns: A = 255 if invalid Memory Pointer
;             otherwise length of string written
;         Y = Last character in string
;         X = Zero Page Memory Pointer
MPUTS:  JSR SETSRC      ;Set Source Pointer
        JSR MERROM      ;Save Memory Pointer & Check Memory Pointer
        BNE MGETCX      ;If Error then Return, Else Y will be 0
        LDA 0,X         ;Copy Memory Pointer LSB 
        STA DSTLO       ;to Source Pointer LSB
        LDA 1,X         ;Copy Memory Pointer MSB
        STA DSTHI       ;to Source Pointer MSB
MPUTSL: LDA (SRCLO),Y   ;Get Character from Memory
        BEQ MPUTSX      ;If Not End of String 
        STA (DSTLO),Y   ;  Store Character in Memory
        TAX             ;  and copy into X Register
        INY             ;  Increment offset and
        BPL MPUTSL      ;  loop if less than 128
MPUTSX: TXA             ;Copy Final Character into Accumulator
        LDX TEMP0       ;Retrieve Memory Pointer
        STY TEMP1       ;Save String Length in TEMP1
        TAY             ;Copy Final Character into Y-Register
MPUTSY: LDA 0,X         ;Get Memory Pointer LSB
        CLC
        ADC TEMP1       ;Add String Length
        STA 0,X
        BCC MGETSZ      ;If Carry
        INC 1,X         ;  Increment Memory Pointer MSB
MGETSZ: LDA TEMP1       ;Load String Length and Set Flags
        RTS

;char mputln(&s) - Write Line to Memory File
MPUTLN: JSR MPUTS       ;Write String to Memory File
        LDA TEMP0       ;Retrieve Memory Pointer
        LDY #RTNKEY     ;Load Carriage Return
        JMP MPUTC       ;Write to Memory File

;mdst(&a) - Set Destination Array for mread()
MDST    EQU SETDST   

;char mread(mp, n) - Read from Memory File into Array
;Args: A = Zero Page Memory Pointer
;      Y = Number of Bytes to Read
;Sets: TEMP0 = Memory Pointer
;      TEMP1 = Number of characters read
;Affects: N,Z reflect Accumulator
;Returns: A,Y = 255 if invalid Memory Pointer
;               otherwise number of bytes read
;         X = Zero Page Memory Pointer
MREAD:  JSR MERRON      ;Save Argumebts & Check Memory Pointer
        BNE MGETCX      ;If Error then Return, Else Y will be 0
        LDA 0,X         ;Copy Memory Pointer LSB 
        STA SRCLO       ;to Source Pointer LSB
        LDA 1,X         ;Copy Memory Pointer MSB
        STA SRCHI       ;to Source Pointer MSB
        BNE MWRITL      ;Execute Copy

;msrc(&a) - Set Source Array for mwrite()
MSRC    EQU SETSRC   

;char mwrite(mp, n) - Read from Memory File into Array
;Args: A = Zero Page Memory Pointer
;      Y = Number of Bytes to Read
;Sets: TEMP0 = Memory Pointer
;      TEMP1 = Number of characters read
;Affects: N,Z reflect Accumulator
;Returns: A,Y = 255 if invalid Memory Pointer
;               otherwise number of bytes written
;         X = Zero Page Memory Pointer
MWRITE: JSR MERRON      ;Save Argumebts & Check Memory Pointer
        BNE MGETCX      ;If Error then Return, Else Y will be 0
        LDA 0,X         ;Copy Memory Pointer LSB 
        STA DSTLO       ;to Destination Pointer LSB
        LDA 1,X         ;Copy Memory Pointer MSB
        STA DSTHI       ;to Destination Pointer MSB
MWRITL: LDA (SRCLO),Y   ;Read Byte from Memory
        STA (DSTLO),Y   ;Write Byte to Array
        INY             ;Increment Index
        CPY TEMP1       ;If Not Equal to Number of Bytes to Read
        BNE MWRITL      ;  Loop
        BEQ MPUTSY      ;Else Update Memory Pointer