;
; Extended memory driver for the VDC RAM available on all C128 machines
; (based on code by Ullrich von Bassewitz)
; Maciej 'YTM/Elysium' Witkowiak <ytm@elysium.pl>
; 06,20.12.2002
.include "zeropage.inc"
.include "em-kernel.inc"
.include "em-error.inc"
.macpack generic
.macpack module
; ------------------------------------------------------------------------
; Header. Includes jump table
module_header _c128_vdc_emd
; Driver signature
.byte $65, $6d, $64 ; "emd"
.byte EMD_API_VERSION ; EM API version number
; Library reference
.addr $0000
; Jump table
.addr INSTALL
.addr UNINSTALL
.addr PAGECOUNT
.addr MAP
.addr USE
.addr COMMIT
.addr COPYFROM
.addr COPYTO
; ------------------------------------------------------------------------
; Constants
VDC_ADDR_REG = $D600 ; VDC address
VDC_DATA_REG = $D601 ; VDC data
VDC_DATA_HI = 18 ; used registers
VDC_DATA_LO = 19
VDC_CSET = 28
VDC_DATA = 31
; ------------------------------------------------------------------------
; Data.
.data
pagecount: .word 64 ; $0000-$3fff as 16k default
curpage: .word $ffff ; currently mapped-in page (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:
; do test for VDC presence here???
ldx #VDC_CSET ; determine size of RAM...
jsr vdcgetreg
sta tmp1
ora #%00010000
jsr vdcputreg ; turn on 64k
jsr settestadr1 ; save original value of test byte
jsr vdcgetbyte
sta tmp2
lda #$55 ; write $55 here
ldy #ptr1
jsr test64k ; read it here and there
lda #$aa ; write $aa here
ldy #ptr2
jsr test64k ; read it here and there
jsr settestadr1
lda tmp2
jsr vdcputbyte ; restore original value of test byte
lda ptr1 ; do bytes match?
cmp ptr1+1
bne @have64k
lda ptr2
cmp ptr2+1
bne @have64k
ldx #VDC_CSET
lda tmp1
jsr vdcputreg ; restore 16/64k flag
jmp @endok ; and leave default values for 16k
@have64k:
lda #<256
ldx #>256
sta pagecount
stx pagecount+1
@endok:
lda #<EM_ERR_OK
ldx #>EM_ERR_OK
rts
test64k:
sta tmp1
sty ptr3
lda #0
sta ptr3+1
jsr settestadr1
lda tmp1
jsr vdcputbyte ; write $55
jsr settestadr1
jsr vdcgetbyte ; read here
pha
jsr settestadr2
jsr vdcgetbyte ; and there
ldy #1
sta (ptr3),y
pla
dey
sta (ptr3),y
rts
settestadr1:
ldy #$02 ; test page 2 (here)
.byte $2c
settestadr2:
ldy #$42 ; or page 64+2 (there)
lda #0
jmp vdcsetsrcaddr
; ------------------------------------------------------------------------
; UNINSTALL routine. Is called before the driver is removed from memory.
; Can do cleanup or whatever. Must not return anything.
;
UNINSTALL:
;on C128 restore font and clear the screen?
rts
; ------------------------------------------------------------------------
; PAGECOUNT: Return the total number of available pages in a/x.
;
PAGECOUNT:
lda pagecount
ldx pagecount+1
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
stx curpage+1
sta ptr1+1
ldy #0
sty ptr1
lda #<window
sta ptr2
lda #>window
sta ptr2+1
jsr transferin
lda #<window
ldx #>window
rts
; copy a single page from (ptr1):VDCRAM to (ptr2):RAM
transferin:
lda ptr1
ldy ptr1+1
jsr vdcsetsrcaddr ; set source address in VDC
ldy #0
ldx #VDC_DATA
stx VDC_ADDR_REG
@L0: bit VDC_ADDR_REG
bpl @L0
lda VDC_DATA_REG ; get 2 bytes at a time to speed-up
sta (ptr2),y ; (in fact up to 8 bytes could be fetched with special VDC config)
iny
lda VDC_DATA_REG
sta (ptr2),y
iny
bne @L0
rts
; ------------------------------------------------------------------------
; USE: Tell the driver that the window is now associated with a given page.
USE: sta curpage
stx curpage+1 ; Remember the page
lda #<window
ldx #>window ; Return the window
done: rts
; ------------------------------------------------------------------------
; COMMIT: Commit changes in the memory window to extended storage.
COMMIT:
lda curpage ; jump if no page mapped
ldx curpage+1
bmi done
sta ptr1+1
ldy #0
sty ptr1
lda #<window
sta ptr2
lda #>window
sta ptr2+1
; fall through to transferout
; copy a single page from (ptr2):RAM to (ptr1):VDCRAM
transferout:
lda ptr1
ldy ptr1+1
jsr vdcsetsrcaddr ; set source address in VDC
ldy #0
ldx #VDC_DATA
stx VDC_ADDR_REG
@L0: bit VDC_ADDR_REG
bpl @L0
lda (ptr2),y ; speedup does not work for writing
sta VDC_DATA_REG
iny
bne @L0
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
beq @L2 ; Skip if no full pages
; Copy full pages
@L1: jsr transferin
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
sta tmp1
; Transfer the bytes in the last page
ldy #0
@L3: jsr vdcgetbyte
sta (ptr2),y
iny
dec tmp1
lda tmp1
bne @L3
@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:
jsr setup
beq @L2 ; Skip if no full pages
; Copy full pages
@L1: jsr transferout
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
sta tmp1
; Transfer the bytes in the last page
ldy #0
@L3: lda (ptr2),y
jsr vdcputbyte
iny
dec tmp1
lda tmp1
bne @L3
@L4: rts
;-------------------------------------------------------------------------
; Helper functions to handle VDC ram
;
vdcsetsrcaddr:
ldx #VDC_DATA_LO
stx VDC_ADDR_REG
@L0: bit VDC_ADDR_REG
bpl @L0
sta VDC_DATA_REG
dex
tya
stx VDC_ADDR_REG
sta VDC_DATA_REG
rts
vdcgetbyte:
ldx #VDC_DATA
vdcgetreg:
stx VDC_ADDR_REG
@L0: bit VDC_ADDR_REG
bpl @L0
lda VDC_DATA_REG
rts
vdcputbyte:
ldx #VDC_DATA
vdcputreg:
stx VDC_ADDR_REG
@L0: bit VDC_ADDR_REG
bpl @L0
sta VDC_DATA_REG
rts
; ------------------------------------------------------------------------
; Helper function for COPYFROM and COPYTO: Store the pointer to the request
; structure and prepare data for the copy
;
setup:
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
sta ptr1+1 ; From
ldy #EM_COPY::BUF
lda (ptr3),y
sta ptr2
iny
lda (ptr3),y
sta ptr2+1 ; To
ldy #EM_COPY::COUNT+1
lda (ptr3),y ; Get number of pages
sta tmp1
rts