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cc65/libsrc/c64/c64-ram.s

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;
; Extended memory driver for the C64 hidden RAM
;
; Ullrich von Bassewitz, 2002-12-02
;
.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 $00 ; EM API version number
; Jump table.
.word INSTALL
.word DEINSTALL
.word PAGECOUNT
.word MAP
.word COMMIT
.word COPYFROM
.word COPYTO
; ------------------------------------------------------------------------
; Constants
BASE = $D000
PAGES = ($10000 - BASE) / 256
; ------------------------------------------------------------------------
; Data.
.data
curpage: .byte $FF ; Current page number (invalid)
.bss
window: .res 256 ; Memory "window"
.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 #<EM_ERR_OK
ldx #>EM_ERR_OK
rts
; ------------------------------------------------------------------------
; DEINSTALL routine. Is called before the driver is removed from memory.
; Can do cleanup or whatever. Must not return anything.
;
DEINSTALL:
rts
; ------------------------------------------------------------------------
; PAGECOUNT: Return the total number of available pages in a/x.
;
PAGECOUNT:
lda #<PAGES
ldx #>PAGES
rts
; ------------------------------------------------------------------------
; 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: sta curpage ; Remember the new page
clc
adc #>BASE
sta ptr1+1
ldy #$00
sty ptr1
lda #<window
sta ptr2
lda #>window
sta ptr2+1
; Transfer one page
jsr transfer ; Transfer one page
; Return the memory window
lda #<window
ldx #>window ; Return the window address
rts
; ------------------------------------------------------------------------
; COMMIT: Commit changes in the memory window to extended storage.
COMMIT: lda curpage ; Get the current page
bmi done ; Jump if no page mapped
clc
adc #>BASE
sta ptr2+1
ldy #$00
sty ptr2
lda #<window
sta ptr1
lda #>window
sta ptr1+1
; Transfer one page. Y must be zero on entry
transfer:
ldx $01 ; Remember c64 control port
txa
and #$F8 ; Bank out ROMs, I/O
sei
sta $01
; Unroll the following loop
loop: lda (ptr1),y
sta (ptr2),y
iny
lda (ptr1),y
sta (ptr2),y
iny
lda (ptr1),y
sta (ptr2),y
iny
lda (ptr1),y
sta (ptr2),y
iny
lda (ptr1),y
sta (ptr2),y
iny
lda (ptr1),y
sta (ptr2),y
iny
lda (ptr1),y
sta (ptr2),y
iny
lda (ptr1),y
sta (ptr2),y
iny
bne loop
; Restore the old memory configuration, allow interrupts
stx $01 ; Restore the old configuration
cli
; Done
done: 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:
sta ptr3
stx ptr3+1 ; Save the passed em_copy pointer
ldy #EM_COPY_OFFS
lda (ptr3),y
sta ptr1
ldy #EM_COPY_PAGE
lda (ptr3),y
clc
adc #>BASE
sta ptr1+1 ; From
ldy #EM_COPY_BUF
lda (ptr3),y
sta ptr2
iny
lda (ptr3),y
sta ptr2+1 ; To
common: ldy #EM_COPY_COUNT+1
lda (ptr3),y ; Get number of pages
beq @L2 ; Skip if no full pages
sta tmp1
; Copy full pages allowing interrupts after each page copied
ldy #$00
@L1: jsr transfer
inc ptr1+1
inc ptr2+1
dec tmp1
bne @L1
; Copy the remainder of the page
@L2: ldy #EM_COPY_COUNT
lda (ptr3),y ; Get bytes in last page
beq @L4
tax
lda $01 ; Remember c64 control port
pha
and #$F8 ; Bank out ROMs, I/O
sei
sta $01
; Transfer the bytes in the last page
@L3: lda (ptr1),y
sta (ptr2),y
iny
dex
bne @L3
; Restore the old memory configuration, allow interrupts
pla
sta $01 ; Restore the old configuration
cli
; Done
@L4: rts
; ------------------------------------------------------------------------
; 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: sta ptr3
stx ptr3+1 ; Save the passed em_copy pointer
ldy #EM_COPY_OFFS
lda (ptr3),y
sta ptr2
ldy #EM_COPY_PAGE
lda (ptr3),y
clc
adc #>BASE
sta ptr2+1 ; To
ldy #EM_COPY_BUF
lda (ptr3),y
sta ptr1
iny
lda (ptr3),y
sta ptr1+1 ; From
jmp common