cc65/libsrc/c64/c64-isepic.s

;
; Extended memory driver for the ISEPIC cartridge.
; Marco van den Heuvel, 2010-01-24
;

        .include	"zeropage.inc"

        .include	"em-kernel.inc"
        .include	"em-error.inc"


        .macpack	generic


; ------------------------------------------------------------------------
; Header. Includes jump table

.segment        "JUMPTABLE"

; Driver signature

        .byte	$65, $6d, $64		; "emd"
        .byte	EMD_API_VERSION		; EM API version number

; Jump table.

        .word	INSTALL
        .word	UNINSTALL
        .word	PAGECOUNT
        .word	MAP
        .word	USE
        .word	COMMIT
        .word	COPYFROM
        .word	COPYTO

; ------------------------------------------------------------------------
; Constants

IP_WINDOW       = $DF00		; Address of ISEPIC window
IP_CTRL_BASE    = $DE00
PAGES           = 8

; ------------------------------------------------------------------------
; Code.

.code

; ------------------------------------------------------------------------
; INSTALL routine. Is called after the driver is loaded into memory. If
; possible, check if the hardware is present and determine the amount of
; memory available.
; Must return an EM_ERR_xx code in a/x.
;

INSTALL:
        lda	#0
        sta	IP_CTRL_BASE
        ldx	IP_WINDOW
        cpx	IP_WINDOW
        bne	@notpresent
        inc	IP_WINDOW
        cpx	IP_WINDOW
        beq	@notpresent
        ldx	IP_WINDOW
        sta	IP_CTRL_BASE+1
        inx
        stx	IP_WINDOW
        dex
        sta	IP_CTRL_BASE
        cpx	IP_WINDOW
        beq	@setok

@notpresent:
        lda	#<EM_ERR_NO_DEVICE
        ldx	#>EM_ERR_NO_DEVICE
        rts

@setok:
        lda	#<EM_ERR_OK
        ldx	#>EM_ERR_OK
;       rts				; Run into UNINSTALL instead

; ------------------------------------------------------------------------
; UNINSTALL routine. Is called before the driver is removed from memory.
; Can do cleanup or whatever. Must not return anything.
;

UNINSTALL:
        rts

; ------------------------------------------------------------------------
; PAGECOUNT: Return the total number of available pages in a/x.
;

PAGECOUNT:
        lda	#<PAGES
        ldx	#>PAGES
        rts

; ------------------------------------------------------------------------
; USE: Tell the driver that the window is now associated with a given page.
; The Isepic cartridge does not copy but actually map the window, so USE is
; identical to MAP.

USE     := MAP

; ------------------------------------------------------------------------
; MAP: Map the page in a/x into memory and return a pointer to the page in
; a/x. The contents of the currently mapped page (if any) may be discarded
; by the driver.
;

MAP:
        tax
        sta	IP_CTRL_BASE,x
        lda	#<IP_WINDOW
        ldx	#>IP_WINDOW

; Use the RTS from COMMIT below to save a precious byte of storage

; ------------------------------------------------------------------------
; COMMIT: Commit changes in the memory window to extended storage.

COMMIT:
        rts

; ------------------------------------------------------------------------
; COPYFROM: Copy from extended into linear memory. A pointer to a structure
; describing the request is passed in a/x.
; The function must not return anything.
;

COPYFROM:
        jsr	setup

; Setup is:
;
;   - ptr1 contains the struct pointer
;   - ptr2 contains the linear memory buffer
;   - ptr3 contains -(count-1)
;   - tmp1 contains the low page register value
;   - X contains the page offset
;   - Y contains zero

        jmp	@L5

@L1:
        lda	IP_WINDOW,x
        sta	(ptr2),y
        iny
        bne	@L2
        inc	ptr2+1
@L2:
        inx
        beq	@L4

; Bump count and repeat

@L3:
        inc	ptr3
        bne	@L1
        inc	ptr3+1
        bne	@L1
        rts

; Bump page register

@L4:
        inc	tmp1		; Bump low page register
@L5:
        stx	tmp2
        ldx	tmp1
        sta	IP_CTRL_BASE,x
        ldx	tmp2
        jmp	@L3

; ------------------------------------------------------------------------
; COPYTO: Copy from linear into extended memory. A pointer to a structure
; describing the request is passed in a/x.
; The function must not return anything.
;

COPYTO:
        jsr	setup

; Setup is:
;
;   - ptr1 contains the struct pointer
;   - ptr2 contains the linear memory buffer
;   - ptr3 contains -(count-1)
;   - tmp1 contains the low page register value
;   - X contains the page offset
;   - Y contains zero

        jmp	@L5

@L1:
        lda	(ptr2),y
        sta	IP_WINDOW,x
        iny
        bne	@L2
        inc	ptr2+1
@L2:
        inx
        beq	@L4

; Bump count and repeat

@L3:
        inc	ptr3
        bne	@L1
        inc	ptr3+1
        bne	@L1
        rts

; Bump page register

@L4:
        inc	tmp1		; Bump page register
@L5:
        stx	tmp2
        ldx	tmp1
        sta	IP_CTRL_BASE,x
        ldx	tmp2
        jmp	@L3

; ------------------------------------------------------------------------
; Helper function for COPYFROM and COPYTO: Store the pointer to the request
; structure and prepare data for the copy

setup:
        sta	ptr1
        stx	ptr1+1		; Save passed pointer

; Get the page number from the struct and remember it.

        ldy	#EM_COPY::PAGE
        lda	(ptr1),y
        sta	tmp1

; Get the buffer pointer into ptr2

        ldy	#EM_COPY::BUF
        lda	(ptr1),y
        sta	ptr2
        iny
        lda	(ptr1),y
        sta	ptr2+1

; Get the count, calculate -(count-1) and store it into ptr3

        ldy	#EM_COPY::COUNT
        lda	(ptr1),y
        eor	#$FF
        sta	ptr3
        iny
        lda	(ptr1),y
        eor	#$FF
        sta	ptr3+1

; Get the page offset into X and clear Y

        ldy	#EM_COPY::OFFS
        lda	(ptr1),y
        tax
        ldy	#0

; Done

        rts