mirror of https://github.com/cc65/cc65.git
252 lines
6.8 KiB
ArmAsm
252 lines
6.8 KiB
ArmAsm
;
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; Extended memory driver for the C64 D2TV (the second or PAL version).
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; Driver works without problems when statically linked.
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;
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; Ullrich von Bassewitz, 2005-11-27
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;
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.include "zeropage.inc"
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.include "em-kernel.inc"
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.include "em-error.inc"
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.import _get_ostype
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.macpack generic
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.macpack module
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; ------------------------------------------------------------------------
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; Header. Includes jump table
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module_header _dtv_himem_emd
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; Driver signature
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.byte $65, $6d, $64 ; "emd"
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.byte EMD_API_VERSION ; EM API version number
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; Library reference
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.addr $0000
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; Jump table
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.addr INSTALL
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.addr UNINSTALL
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.addr PAGECOUNT
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.addr MAP
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.addr USE
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.addr COMMIT
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.addr COPYFROM
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.addr COPYTO
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; ------------------------------------------------------------------------
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; Constants
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OP_COPYFROM = %00001101
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OP_COPYTO = %00001111
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START_BANK = 2 ; Start at $20000
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PAGES = (2048 - 128) * 4
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; ------------------------------------------------------------------------
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; Data.
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.bss
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window: .res 256 ; Memory "window"
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.data
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; The MAP and COMMIT entries will actually call COPYFROM/COPYTO with
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; a pointer to the following data structure:
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dma_params: .word window ; Host address
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.byte 0 ; Offset in page
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curpage: .word $0000 ; Page
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.word .sizeof (window); # bytes to move, lo, hi
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.code
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; ------------------------------------------------------------------------
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; INSTALL routine. Is called after the driver is loaded into memory. If
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; possible, check if the hardware is present and determine the amount of
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; memory available.
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; Must return an EM_ERR_xx code in a/x.
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;
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INSTALL:
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; Check for a DTV
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ldx #1
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stx $d03f
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ldx $d040
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cpx $d000
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bne @present
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inc $d000
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cpx $d040
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beq @present
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dec $d000
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; DTV not found
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lda #EM_ERR_NO_DEVICE
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ldx #0 ; return value is char
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rts
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@present:
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ldx #$FF
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stx curpage+1 ; Invalidate curpage
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.assert EM_ERR_OK = 0, error
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inx
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txa
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; rts ; Run into UNINSTALL instead
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; ------------------------------------------------------------------------
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; UNINSTALL routine. Is called before the driver is removed from memory.
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; Can do cleanup or whatever. Must not return anything.
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;
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UNINSTALL:
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rts
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; ------------------------------------------------------------------------
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; PAGECOUNT: Return the total number of available pages in a/x.
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;
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PAGECOUNT:
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lda #<PAGES
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ldx #>PAGES
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rts
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; ------------------------------------------------------------------------
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; MAP: Map the page in a/x into memory and return a pointer to the page in
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; a/x. The contents of the currently mapped page (if any) may be discarded
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; by the driver.
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;
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MAP: sta curpage
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stx curpage+1 ; Remember the new page
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lda #<dma_params
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ldx #>dma_params
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jsr COPYFROM ; Copy data into the window
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lda #<window
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ldx #>window ; Return the window address
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done: rts
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; ------------------------------------------------------------------------
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; USE: Tell the driver that the window is now associated with a given page.
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USE: sta curpage
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stx curpage+1 ; Remember the page
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lda #<window
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ldx #>window ; Return the window
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rts
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; ------------------------------------------------------------------------
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; COMMIT: Commit changes in the memory window to extended storage.
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COMMIT: lda curpage+1 ; Do we have a page mapped?
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bmi done ; Jump if no page mapped
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lda #<dma_params
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ldx #>dma_params
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; Run into COPYTO
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; ------------------------------------------------------------------------
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; COPYTO: Copy from linear into extended memory. A pointer to a structure
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; describing the request is passed in a/x.
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; The function must not return anything.
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;
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COPYTO: sta ptr1
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stx ptr1+1 ; Save the pointer
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ldx #OP_COPYTO ; Load the command
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bne transfer
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; ------------------------------------------------------------------------
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; COPYFROM: Copy from extended into linear memory. A pointer to a structure
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; describing the request is passed in a/x.
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; The function must not return anything.
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;
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COPYFROM:
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sta ptr1
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stx ptr1+1 ; Save the pointer
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ldx #OP_COPYFROM
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; DTV DMA transfer routine. Expects the command in X.
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; NOTE: We're using knowledge about field order in the EM_COPY struct here!
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transfer:
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jsr WAIT ; Wait until DMA is finished
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; Modulo disable
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ldy #$00
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sty $d31e
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; Setup the target address and the source and target steps. Y contains zero,
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; which is EM_COPY::BUF.
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sty $d307 ; Source step high = 0
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sty $d309 ; Dest step high = 0
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lda (ptr1),y
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sta $d303 ; Dest address low
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iny ; Y = 1
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sty $d306 ; Source step low = 1
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sty $d308 ; Dest step low = 1
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lda (ptr1),y
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sta $d304
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lda #$40 ; Dest is always RAM, start at $00000
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sta $d305
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; Setup the source address. Incrementing Y will make it point to EM_COPY::OFFS.
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; We will allow page numbers higher than PAGES and map them to ROM. This will
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; allow reading the ROM by specifying a page starting with PAGES.
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iny ; EM_COPY::OFFS
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lda (ptr1),y
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sta $d300
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iny ; EM_COPY::PAGE
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lda (ptr1),y
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sta $d301
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iny
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lda (ptr1),y
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adc #START_BANK ; Carry clear here from WAIT
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and #$3f
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cmp #>PAGES+START_BANK ; Valid range?
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bcs @L1 ; Jump if no
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ora #$40 ; Address RAM
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@L1: sta $d302
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; Length
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iny ; EM_COPY::COUNT
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lda (ptr1),y
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sta $d30a
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iny
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lda (ptr1),y
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sta $d30b
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; Start DMA
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stx $d31f
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; Wait until DMA is done
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WAIT: lda $d31f
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lsr a
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bcs WAIT
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rts
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