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cc65/libsrc/c64/emd/c64-kerberos.s
2023-02-26 20:03:41 +01:00

282 lines
6.9 KiB
ArmAsm

; Extended Memory Driver for the Kerberos MIDI interface.
; http://www.frank-buss.de/kerberos/
; based on the code for RamCart 64/128KB cartridge.
; 2020-06-16 Dirk Jagdmann <doj@cubic.org>
.include "zeropage.inc"
.include "em-kernel.inc"
.include "em-error.inc"
.macpack generic
.macpack module
; ------------------------------------------------------------------------
; Header. Includes jump table
module_header _c64_kerberos_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
RAMC_WINDOW = $DF00 ; Address of Kerberos SRAM
RAMC_PAGE_LO = $DE3E ; Page register low
RAMC_PAGE_HI = $DE3F ; Page register high
.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:
;; write $55 into first page
lda #0
sta RAMC_PAGE_LO
sta RAMC_PAGE_HI
lda #$55
sta RAMC_WINDOW
;; write $AA into second page
lda #1
sta RAMC_PAGE_LO
sta RAMC_PAGE_HI
lda #$AA
sta RAMC_WINDOW
;; check $55 in first page
lda #0
sta RAMC_PAGE_LO
sta RAMC_PAGE_HI
lda RAMC_WINDOW
cmp #$55
bne @notpresent
;; check $AA in first page
lda #1
sta RAMC_PAGE_LO
sta RAMC_PAGE_HI
lda RAMC_WINDOW
cmp #$AA
bne @notpresent
lda #EM_ERR_OK
.assert EM_ERR_OK = 0, error
tax
rts
@notpresent:
lda #EM_ERR_NO_DEVICE
ldx #0 ; return value is char
; use rts from UNINSTALL below
; ------------------------------------------------------------------------
; 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 #<(128 * 1024 / 256)
ldx #>(128 * 1024 / 256)
rts
; ------------------------------------------------------------------------
; USE: Tell the driver that the window is now associated with a given page.
; The Kerberos 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: sta RAMC_PAGE_LO
txa
and #1
sta RAMC_PAGE_HI
lda #<RAMC_WINDOW
ldx #>RAMC_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
; - tmp2 contains the high page register value
; - X contains the page offset
; - Y contains zero
beq @L5 ; will always branch, because setup ends with ldy #0
@L1: lda RAMC_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
bne @L5
inc tmp2
@L5: lda tmp1
sta RAMC_PAGE_LO
lda tmp2
sta RAMC_PAGE_HI
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
; - tmp2 contains the high page register value
; - X contains the page offset
; - Y contains zero
beq @L5 ; will always branch, because setup ends with ldy #0
@L1: lda (ptr2),y
sta RAMC_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
bne @L5
inc tmp2
@L5: lda tmp1
sta RAMC_PAGE_LO
lda tmp2
sta RAMC_PAGE_HI
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 adjust it so that it may be used
; with the hardware. That is: lower 6 bits in tmp1, high bits in tmp2.
ldy #EM_COPY::PAGE+1
lda (ptr1),y
sta tmp2
dey
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 #$00
; Done
rts