cc65/libsrc/atari/shadow_ram_handlers.s

;
; Atari XL shadow RAM handlers
;
; Christian Groessler, chris@groessler.org, 2013
;

;DEBUG           =       1
CHKBUF          =       1       ; check if bounce buffering is needed (bounce buffering is always done if set to 0)

.ifdef __ATARIXL__

SHRAM_HANDLERS  =       1
        .include        "atari.inc"
        .include        "save_area.inc"
        .include        "zeropage.inc"
        .include        "romswitch.inc"

        .import         __CHARGEN_START__

        .export         sram_init
        .export         KEYBDV_handler
        .export         CIO_handler
        .export         SIO_handler
        .export         SETVBV_handler
        .export         XMOVE_handler

BUFSZ           =       128     ; bounce buffer size
BUFSZ_SIO       =       256

.segment "ONCE"

; Turn off ROMs, install system and interrupt wrappers, set new chargen pointer

sram_init:

; disable all interrupts
        ldx     #0
        stx     NMIEN           ; disable NMI
        sei

; disable ROMs
        disable_rom

; setup interrupt vectors
        lda     #<my_IRQ_han
        sta     $fffe
        lda     #>my_IRQ_han
        sta     $ffff

        lda     #<my_RESET_han
        sta     $fffc
        lda     #>my_RESET_han
        sta     $fffd

        lda     #<my_NMI_han
        sta     $fffa
        lda     #>my_NMI_han
        sta     $fffb

; enable interrupts
        cli
        lda     #$40
        sta     NMIEN

        rts

.segment        "EXTZP" : zeropage

zpptr1: .res    2


.segment "LOWBSS"

; bounce buffers for CIO and SIO calls
bounce_buffer:  .res    BUFSZ_SIO


.segment "LOWCODE"


; Interrupt handlers
; ------------------

; The interrupt handlers don't look at the current state of PORTB and
; unconditionally disable the ROMs on exit.
; Please note that this works, since if the ROMs are enabled we anyway
; aren't being called here because the vectors are pointing to their
; original ROM locations.

.macro  int_wrap orgvec
        .local  ret
        pha
        enable_rom_quick
        lda     #>ret
        pha
        lda     #<ret
        pha
        php
        jmp     (orgvec)
ret:    disable_rom_quick
        pla
        rti
.endmacro

my_IRQ_han:
.ifdef DEBUG
        php
        pha
        tya
        pha
        ldy     #0
        lda     (SAVMSC),y
        clc
        adc     #1
        sta     (SAVMSC),y
        pla
        tay
        pla
        plp
.endif
        int_wrap $FFFE

my_NMI_han:
.ifdef DEBUG
        php
        pha
        tya
        pha
        ldy     #39
        lda     (SAVMSC),y
        clc
        adc     #1
        sta     (SAVMSC),y
        pla
        tay
        pla
        plp
.endif
; set I bit to interrupted value
        pha
        txa
        pha
        tsx
        lda     $103,x
        pha
        plp
        pla
        tax
        pla
        int_wrap $FFFA

my_RESET_han:
        enable_rom
        jmp     ($FFFC)


; System request handlers
; -----------------------


; for filenames we assume they will fit into our bounce buffer

; one filename, terminated by "invalid character", located at ICBAL/ICBAH

CIO_filename:
.if CHKBUF
        jsr     chk_CIO_buf_fn
        bcc     CIO_call_a
.endif
        jsr     setup_zpptr1_y0
        jsr     copy_filename
CIO_fn_cont:
        jsr     bncbuf_to_iocb
        ldy     CIO_y
        jsr     CIO_call_a              ; call CIO (maybe A isn't needed, then we could call CIO_call)
        php
        pha
        jsr     restore_icba            ; restore original ICBAL/ICBAH
        pla
        plp
        rts                             ; back to application


; two filenames, terminated and separated by "invalid character", located at ICBAL/ICBAH

CIO_filename2:
.if CHKBUF
        jsr     chk_CIO_buf_fn2
        bcc     CIO_call_a
.endif
        jsr     setup_zpptr1_y0
        jsr     copy_filename
        iny
        jsr     copy_filename
        jmp     CIO_fn_cont



; CIO handler
; We have buffer pointer and length entries in the IOCB, but their
; usage depends on the function.
; Some functions don't care about any of them (pointer and length),
; and some only use the pointer (like e.g. OPEN), and some use both.
; So we need function specific handlers to correctly deal with
; buffers which are overlapping with the ROM area.
;
; FIXME: Currently only the requests used by the runtime lib are handled.

CIO_handler:

; @@@ TODO: check X for valid IOCB index ((X < $80) and ((X & $F) == 0))

        sta     CIO_a
        sty     CIO_y
        stx     CIO_x

        lda     ICCOM,x                 ; get function
        cmp     #OPEN
        beq     CIO_filename            ; filename as input parameter in buffer, length not used
        cmp     #PUTREC
        bcc     CIO_read                ; input (GETREC or GETCHR)
        cmp     #CLOSE
        bcc     CIO_write_jmp           ; output (PUTREC or PUTCHR)
        beq     CIO_call_a              ; pass through, buffer not used
        cmp     #RENAME                 ; 2 filenames as input parameters in buffer, length not used
        beq     CIO_filename2
        cmp     #GETCWD
        bcc     CIO_filename            ; filename as input parameter in buffer, length not used
        beq     CIO_invalid             ; GETCWD not supported yet
        bcs     CIO_call_a              ; other commands: assume no buffer
; not reached

; enable ROM, call CIO, disable ROM

CIO_call_a:
        lda     CIO_a

CIOV_call:
        pha
        lda     PORTB
        sta     cur_CIOV_PORTB
        enable_rom
        pla
        jsr     CIOV_org
        php
        pha
        disable_rom_val cur_CIOV_PORTB
        pla
        plp
        rts


CIO_write_jmp:
        jmp     CIO_write

CIO_invalid:
        lda     CIO_a
        ldy     #DINVCM
        rts

; READ handler
; ------------

CIO_read:
        lda     ICBLL,x
        ora     ICBLH,x
        beq     CIO_call_a              ; special I/O through A register in case buffer length is 0

.if CHKBUF
        jsr     chk_CIO_buf
        bcc     CIO_call_a
.endif

; If the data length is larger than our bounce buffer, we have to split the request into smaller ones.
; Otherwise we can get away with one call and a copy to the final destination afterwards.

        lda     ICBLH,x                 ; get high byte of length
        bne     big_read                ; not zero -> data too large for our buffers
                                        ; CHANGE HERE TO SUPPORT BOUNCE BUFFERS > 255 BYTES
        lda     #<BUFSZ
        cmp     ICBLL,x
        bcc     big_read

; Data size fits into bounce buffer

        jsr     setup_zpptr1
        jsr     bncbuf_to_iocb
        jsr     CIO_call_a              ; call CIO
        php
        bpl     @no_err
        cpy     #EOFERR
        beq     @no_err
        pha
        jsr     restore_icba
        pla
        plp
        rts                             ; return with error

@no_err:
        sta     CIO_a
        sty     CIO_y

        jsr     copy_to_user            ; copy data into user buffer
        jsr     restore_icba

        lda     CIO_a
        ldy     CIO_y
        plp
        rts                             ; return with success

; Data size does not fit into bounce buffer

big_read:
        lda     #0
        sta     retlen                  ; initialize return length
        sta     retlen+1
        jsr     iocblen_to_orig_len
        jsr     iocbptr_to_orig_ptr
        jsr     setup_zpptr1
        jsr     bncbuf_to_iocb          ; let ICBAL/ICBAH point to bounce buffer

br_loop:
        jsr     cmp_orig_len_bnc_bufsz  ; is transfer length > bounce buffer size?
        bcs     br_last                 ; no, last transfer, use remaining size

        lda     #>BUFSZ
        sta     ICBLH,x                 ; set data length
        lda     #<BUFSZ
        sta     ICBLL,x
        bne     br_cont

br_last:
        lda     orig_len+1
        sta     ICBLH,x                 ; set data length
        lda     orig_len
        sta     ICBLL,x

br_cont:
        sta     req_len                 ; remember length of this request
        lda     ICBLH,x
        sta     req_len+1
        jsr     CIO_call_a              ; do the request
        php
        bpl     br_no_err
        cpy     #EOFERR
        beq     br_no_err

        pha
        jsr     restore_icba
        pla
        plp
        rts                             ; return with error

br_no_err:
        sta     CIO_a
        sty     CIO_y
        pla
        sta     CIO_p
        jsr     copy_to_user

; update retlen
        clc
        lda     retlen
        adc     ICBLL,x
        sta     retlen
        lda     retlen+1
        adc     #0
        sta     retlen+1

; if the request read less bytes than requested, we're done
        lda     ICBLL,x
        cmp     req_len
        bne     br_done
        lda     ICBLH,x
        cmp     req_len+1
        bne     br_done

; update user buffer pointer (zpptr1)
        clc
        lda     zpptr1
        adc     ICBLL,x
        sta     zpptr1
        lda     zpptr1+1
        adc     #0
        sta     zpptr1+1

; update remaining length
        sec
        lda     orig_len
        sbc     ICBLL,x
        sta     orig_len
        lda     orig_len+1
        sbc     #0
        sta     orig_len+1

; still something left to do (remaining length != 0)?
        lda     orig_len
        ora     orig_len+1
        beq     br_done
        jmp     br_loop

; done, write original buffer pointer and total transfer length to IOCB and return to application
br_done:
        lda     retlen
        sta     ICBLL,x
        lda     retlen+1
        sta     ICBLH,x
        jsr     orig_ptr_to_iocbptr
        lda     CIO_p
        pha
        lda     CIO_a
        ldy     CIO_y
        plp
        rts                             ; return with success



CIO_call_a_jmp:
        jmp     CIO_call_a



; WRITE handler
; -------------


CIO_write:
        lda     ICBLL,x
        ora     ICBLH,x
        beq     CIO_call_a_jmp          ; special I/O through A register in case buffer length is 0

.if CHKBUF
        jsr     chk_CIO_buf
        bcc     CIO_call_a_jmp
.endif

; If the data length is larger than our bounce buffer, we have to split the request into smaller ones.
; Otherwise we can get away with a copy to the bounce buffer and the call.

        lda     ICBLH,x                 ; get high byte of length
        bne     big_write               ; not zero -> data too large for our buffers
                                        ; CHANGE HERE TO SUPPORT BOUNCE BUFFERS > 255 BYTES
        lda     #<BUFSZ
        cmp     ICBLL,x
        bcc     big_write


; Data size fits into bounce buffer

        jsr     setup_zpptr1
        jsr     bncbuf_to_iocb
        jsr     copy_from_user
        ldy     CIO_y
        jsr     CIO_call_a
        php
        pha
        jsr     restore_icba
        pla
        plp
        rts                             ; return to application


; Data size does not fit into bounce buffer

big_write:
        lda     #0
        sta     retlen                  ; initialize return length
        sta     retlen+1
        jsr     iocblen_to_orig_len
        jsr     iocbptr_to_orig_ptr
        jsr     setup_zpptr1
        jsr     bncbuf_to_iocb          ; let ICBAL/ICBAH point to bounce buffer

bw_loop:
        jsr     cmp_orig_len_bnc_bufsz  ; is transfer length > bounce buffer size?
        bcs     bw_last                 ; no, last transfer, use remaining size

        lda     #>BUFSZ
        sta     ICBLH,x                 ; set data length
        lda     #<BUFSZ
        sta     ICBLL,x
        bne     bw_cont

bw_last:
        lda     orig_len+1
        sta     ICBLH,x                 ; set data length
        lda     orig_len
        sta     ICBLL,x

bw_cont:
        sta     req_len                 ; remember length of this request
        lda     ICBLH,x
        sta     req_len+1
        jsr     copy_from_user
        jsr     CIO_call_a              ; do the request
        php
        bpl     bw_no_err

        plp
        rts                             ; error return

bw_no_err:
        sta     CIO_a
        sty     CIO_y
        pla
        sta     CIO_p

; update retlen
        clc
        lda     retlen
        adc     ICBLL,x
        sta     retlen
        lda     retlen+1
        adc     #0
        sta     retlen+1

; if the request wrote less bytes than requested, we're done
        lda     ICBLL,x
        cmp     req_len
        bne     bw_done
        lda     ICBLH,x
        cmp     req_len+1
        bne     bw_done

; update user buffer pointer (zpptr1)
        clc
        lda     zpptr1
        adc     ICBLL,x
        sta     zpptr1
        lda     zpptr1+1
        adc     #0
        sta     zpptr1+1

; update remaining length
        sec
        lda     orig_len
        sbc     ICBLL,x
        sta     orig_len
        lda     orig_len+1
        sbc     #0
        sta     orig_len+1

; still something left to do (remaining length != 0)?
        lda     orig_len
        ora     orig_len+1
        beq     bw_done
        jmp     bw_loop

bw_done:
        lda     retlen
        sta     ICBLL,x
        lda     retlen+1
        sta     ICBLH,x
        jsr     orig_ptr_to_iocbptr
        lda     CIO_p
        pha
        lda     CIO_a
        ldy     CIO_y
        plp
        rts                             ; return with success



; check if length is larger than bounce buffer size
; input:   orig_len - length
; output:         A - destroyed
;                CF - 0/1 for larger/not larger
cmp_orig_len_bnc_bufsz:
        sec
        lda     #<BUFSZ
        sbc     orig_len
        lda     #>BUFSZ
        sbc     orig_len+1
        rts


; copy data from bounce buffer into user buffer
; input:   X - IOCB index
;     zpptr1 - pointer to user buffer
; output:  A - destroyed
;          Y - 0
copy_to_user:
        ldy     ICBLL,x                 ; get # of bytes read (CHANGE HERE TO SUPPORT BOUNCE BUFFERS > 255 BYTES)
        beq     @copy_done
@copy:  dey
        lda     bounce_buffer,y
        sta     (zpptr1),y
        cpy     #0
        bne     @copy
@copy_done:
        rts


; copy data from user buffer into bounce buffer
; input:   X - IOCB index
;     zpptr1 - pointer to user buffer
; output:  A - destroyed
;          Y - 0
copy_from_user:
        ldy     ICBLL,x                 ; get # of bytes to write (CHANGE HERE TO SUPPORT BOUNCE BUFFERS > 255 BYTES)
        beq     @copy_done
@copy:  dey
        lda     (zpptr1),y
        sta     bounce_buffer,y
        cpy     #0
        bne     @copy
@copy_done:
        rts


; copy ICBLL/ICBLH to 'orig_len'
; input:   X - IOCB index
; output:  A - destroyed
iocblen_to_orig_len:
        lda     ICBLL,x
        sta     orig_len
        lda     ICBLH,x
        sta     orig_len+1
        rts


; copy ICBAL/ICBAH to 'orig_ptr'
; input:   X - IOCB index
; output:  A - destroyed
iocbptr_to_orig_ptr:
        lda     ICBAL,x
        sta     orig_ptr
        lda     ICBAH,x
        sta     orig_ptr+1
        rts


; copy 'orig_ptr' to ICBAL/ICBAH
; input:   X - IOCB index
; output:  A - destroyed
orig_ptr_to_iocbptr:
        lda     orig_ptr
        sta     ICBAL,x
        lda     orig_ptr+1
        sta     ICBAH,x
        rts


; restore original contents of ICBAL/ICBAH from 'zpptr1'
; input:   X - IOCB index
; output:  A - destroyed
restore_icba:
        lda     zpptr1
        sta     ICBAL,x
        lda     zpptr1+1
        sta     ICBAH,x
        rts


; put bounce buffer address into ICBAL/ICBAH
; input:   X - IOCB index
; output:  A - destroyed
bncbuf_to_iocb:
        lda     #<bounce_buffer
        sta     ICBAL,x
        lda     #>bounce_buffer
        sta     ICBAH,x
        rts


; copy file name pointed to by 'zpptr1' to 'bounce_buffer'
; input:   Y - index into file name buffer and bounce_buffer
; output:  Y - points to first invalid byte after file name
;          A - destroyed
copy_filename:
        lda     (zpptr1),y
        sta     bounce_buffer,y
        beq     copy_fn_done
        iny
        cmp     #ATEOL
        bne     copy_filename
        dey
copy_fn_done:
        rts


; write IOCB buffer address into zpptr1
; input:   X - IOCB index
; output:  Y - 0 (for setup_zpptr1_y0, else unchanged)
;          A - destroyed
setup_zpptr1_y0:
        ldy     #0
setup_zpptr1:
        lda     ICBAL,x                 ; put buffer address into zp pointer
        sta     zpptr1
        lda     ICBAH,x
        sta     zpptr1+1
        rts


.if CHKBUF

; get length of file name pointed to by 'zpptr1'
; input:   Y - index into file name
; output:  Y - length
;          A - destroyed
get_fn_len:
        lda     (zpptr1),y
        beq     @done
        iny
        cmp     #ATEOL
        bne     get_fn_len
        dey
@done:
        rts


chk_CIO_buf_fn2:
        tya
        pha
        lda     ICBLL,x
        pha
        lda     ICBLH,x
        pha
        jsr     setup_zpptr1_y0
        jsr     get_fn_len
        iny                     ; include terminating zero
        bne     fn_cont

chk_CIO_buf_fn:
        tya
        pha
        lda     ICBLL,x
        pha
        lda     ICBLH,x
        pha
        jsr     setup_zpptr1_y0
fn_cont:jsr     get_fn_len
        iny                     ; include terminating zero
        tya
        sta     ICBLL,x
        lda     #0
        sta     ICBLH,x
        jsr     chk_CIO_buf
        pla     
        sta     ICBLH,x
        pla     
        sta     ICBLL,x
        pla
        tay
        rts


; check if a CIO input/output buffer overlaps with ROM area (>= $C000)
; input:                      X - IOCB index
;       ICBAL/ICBAH/ICBLL/ICBLH - buffer address and length
; output:                    CF - 1/0 for overlap/no overlap
;                             A - destroyed

chk_CIO_buf:
        lda     ICBAH,x
        cmp     #$c0
        bcc     @cont
@ret:   
.ifdef DEBUG
        jsr     CIO_buf_noti
.endif
        rts

@cont:  lda     ICBAL,x
        clc
        adc     ICBLL,x
        lda     ICBAH,x
        adc     ICBLH,x
        bcs     @ret            ; ??? wraparound
        cmp     #$c0
.ifdef DEBUG
        jsr     CIO_buf_noti
.endif
        rts

.ifdef DEBUG
; write to screen memory on 2nd line:
; pos 0: # of accesses without buffering
; pos 1: # of accesses with buffering
CIO_buf_noti:
        php
        pha
        tya
        pha
        bcc     @nobuf

        inc     CIObnval_dobuf
        jmp     @cont

@nobuf: inc     CIObnval_nobuf

@cont:  ldy     #40
        lda     CIObnval_nobuf
        sta     (SAVMSC),y
        ldy     #41
        lda     CIObnval_dobuf
        sta     (SAVMSC),y

        pla
        tay
        pla
        plp
        rts

CIObnval_dobuf:
        .byte   0
CIObnval_nobuf:
        .byte   0
.endif

.endif  ; .if CHKBUF

;---------------------------------------------------------

; SIO handler
; We only handle SIO_STAT, SIO_READ, SIO_WRITE, and SIO_WRITEV.
; These are the only functions used by the runtime library currently.
; For other function we return NVALID status code.

SIO_handler:
        lda     DCOMND                  ; get command
        cmp     #SIO_STAT
        beq     SIO_stat
        cmp     #SIO_READ
        beq     SIO_read
        cmp     #SIO_WRITE
        beq     SIO_write
        cmp     #SIO_WRITEV
        beq     SIO_write

        ; unhandled command
        lda     #NVALID
SIO_err:sta     DSTATS
        rts

; SIO_STAT is always called with a low buffer (by the runtime)
SIO_stat:
        ; fall thru

SIO_call:
        lda     PORTB
        sta     cur_SIOV_PORTB
        enable_rom
        jsr     SIOV_org
        php
        pha
        disable_rom_val cur_SIOV_PORTB
        pla
        plp
        rts


; SIO read handler
; ----------------

SIO_read:

.if CHKBUF
        jsr     chk_SIO_buf
        bcc     SIO_call
.endif

; we only support transfers <= bounce buffer size
        jsr     cmp_sio_len_bnc_bufsz
        bcs     sio_read_len_ok

        lda     #DERROR         ; don't know a better status code for this
        bne     SIO_err

sio_read_len_ok:
        lda     DBUFLO
        sta     zpptr1          ; remember destination buffer address
        lda     DBUFHI
        sta     zpptr1+1

        jsr     bncbuf_to_dbuf  ; put bounce buffer address to DBUFLO/DBUFHI

        jsr     SIO_call        ; do the operation
        pha
        lda     DSTATS          ; get status
        bmi     sio_read_ret    ; error

        ; copy data to user buffer
sio_read_ok:
        lda     DBYTHI          ; could be 1 for 256 bytes
        beq     srok1
        ldy     #0
        beq     srok2
srok1:  ldy     DBYTLO
srok2:  dey
sio_read_copy:
        lda     bounce_buffer,y
        sta     (zpptr1),y
        dey
        cpy     #$ff
        bne     sio_read_copy

sio_read_ret:
        jsr     orgbuf_to_dbuf

        pla
        rts                     ; success return


; SIO write handler
; -----------------

SIO_write:

.if CHKBUF
        jsr     chk_SIO_buf
        bcc     SIO_call
.endif

; we only support transfers <= bounce buffer size
        jsr     cmp_sio_len_bnc_bufsz
        bcs     sio_write_len_ok

        lda     #DERROR         ; don't know a better status code for this
        jmp     SIO_err

sio_write_len_ok:
        lda     DBUFLO
        sta     zpptr1          ; get source buffer address
        lda     DBUFHI
        sta     zpptr1+1

        ; copy data from user buffer to bounce buffer
        lda     DBYTHI          ; could be 1 for 256 bytes
        beq     swok1
        ldy     #0
        beq     swok2
swok1:  ldy     DBYTLO
swok2:  dey
sio_write_copy:
        lda     (zpptr1),y
        sta     bounce_buffer,y
        dey
        cpy     #$ff
        bne     sio_write_copy

        jsr     bncbuf_to_dbuf  ; put bounce buffer address to DBUFLO/DBUFHI

        jsr     SIO_call        ; do the operation
        pha
        jsr     orgbuf_to_dbuf
        pla
        rts


; check if SIO length is larger than bounce buffer size
; input:   orig_len - length
; output:         A - destroyed
;                CF - 0/1 for larger/not larger
cmp_sio_len_bnc_bufsz:
        sec
        lda     #<BUFSZ_SIO
        sbc     DBYTLO
        lda     #>BUFSZ_SIO
        sbc     DBYTHI
        rts

; put bounce buffer address into DBUFLO/DBUFHI
; input:   (--)
; output:  A - destroyed
bncbuf_to_dbuf:
        lda     #<bounce_buffer
        sta     DBUFLO
        lda     #>bounce_buffer
        sta     DBUFHI
        rts

; put original buffer address into DBUFLO/DBUFHI
; input:   zpptr1 - original pointer
; output:  A      - destroyed
orgbuf_to_dbuf:
        lda     zpptr1
        sta     DBUFLO
        lda     zpptr1+1
        sta     DBUFHI
        rts


.if CHKBUF

; check if a SIO input/output buffer overlaps with ROM area (>= $C000)
; input: DBUFLO/DBUFHI/DBYTLO/DBYTHI - buffer address and length
; output:                         CF - 1/0 for overlap/no overlap
;                                  A - destroyed

chk_SIO_buf:
        lda     DBUFHI
        cmp     #$c0
        bcc     @cont
@ret:
.ifdef DEBUG
        jsr     SIO_buf_noti
.endif
        rts

@cont:  lda     DBUFLO
        clc
        adc     DBYTLO
        lda     DBUFHI
        adc     DBYTHI
        bcs     @ret            ; ??? wraparound
        cmp     #$c0
.ifdef DEBUG
        jsr     SIO_buf_noti
.endif
        rts

.ifdef DEBUG
; write to screen memory on 2nd line:
; pos 38: # of accesses without buffering
; pos 39: # of accesses with buffering
SIO_buf_noti:
        php
        pha
        tya
        pha
        bcc     @nobuf

        inc     SIObnval_dobuf
        jmp     @cont

@nobuf: inc     SIObnval_nobuf

@cont:  ldy     #78
        lda     SIObnval_nobuf
        sta     (SAVMSC),y
        ldy     #79
        lda     SIObnval_dobuf
        sta     (SAVMSC),y

        pla
        tay
        pla
        plp
        rts

SIObnval_dobuf:
        .byte   0
SIObnval_nobuf:
        .byte   0
.endif

.endif  ; .if CHKBUF

;---------------------------------------------------------

KEYBDV_handler:

        lda     #>(kret-1)
        pha
        lda     #<(kret-1)
        pha
        lda     PORTB
        sta     cur_KEYBDV_PORTB
        enable_rom
        lda     KEYBDV+5
        pha
        lda     KEYBDV+4
        pha
        rts             ; call keyboard handler
kret:   pha
        disable_rom_val cur_KEYBDV_PORTB
        pla
        rts

;---------------------------------------------------------

SETVBV_handler:

        pha
        lda     PORTB
        sta     cur_SETVBV_PORTB
        enable_rom
        pla
        jsr     SETVBV_org
        php
        pha
        disable_rom_val cur_SETVBV_PORTB
        pla
        plp
        rts

;---------------------------------------------------------

XMOVE_handler:

        pha
        lda     PORTB
        sta     cur_XMOVE_PORTB
        enable_rom
        pla
        jsr     XMOVE_org
        php
        pha
        disable_rom_val cur_XMOVE_PORTB
        pla
        plp
        rts


CIO_a:                  .res    1
CIO_x:                  .res    1
CIO_y:                  .res    1
CIO_p:                  .res    1
cur_CIOV_PORTB:         .res    1
cur_SIOV_PORTB:         .res    1
cur_KEYBDV_PORTB:       .res    1
cur_SETVBV_PORTB:       .res    1
cur_XMOVE_PORTB:        .res    1
orig_ptr:               .res    2
orig_len:               .res    2
req_len:                .res    2
retlen:                 .res    2

.endif  ; .ifdef __ATARIXL__