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cc65/libsrc/c64/c64-isepic.s

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;
; 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