mirror of https://github.com/cc65/cc65.git
260 lines
6.3 KiB
ArmAsm
260 lines
6.3 KiB
ArmAsm
;
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; Extended memory driver for the VIC20 $A000-$BFFF RAM. Driver works without
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; problems when statically linked.
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;
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; Marco van den Heuvel, 2018-03-16
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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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.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 _vic20_rama_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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BASE = $A000
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PAGES = ($C000 - BASE) / 256
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; ------------------------------------------------------------------------
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; Data.
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.bss
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curpage: .res 1 ; Current page number
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window: .res 256 ; Memory "window"
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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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lda $A000 ; see what is at address $A000
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inc $A000 ; see if it can be changed
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cmp $A000 ; did it stick ?
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beq nomem
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dec $A000
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ldx #$FF
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stx curpage ; Invalidate the current page
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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
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nomem: ldx #0 ; return value is char
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lda #EM_ERR_NO_DEVICE
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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 ; Remember the new page
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clc
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adc #>BASE
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sta ptr1+1
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ldy #$00
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sty ptr1
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lda #<window
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sta ptr2
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lda #>window
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sta ptr2+1
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; Transfer one page
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jsr transfer ; Transfer one page
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; Return the memory window
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lda #<window
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ldx #>window ; Return the window address
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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 ; 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 ; Get the current page
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bmi done ; Jump if no page mapped
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clc
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adc #>BASE
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sta ptr2+1
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ldy #$00
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sty ptr2
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lda #<window
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sta ptr1
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lda #>window
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sta ptr1+1
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; Transfer one page. Y must be zero on entry
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transfer:
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; Unroll the following loop
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loop: .repeat 8
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lda (ptr1),y
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sta (ptr2),y
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iny
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.endrepeat
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bne loop
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; Done
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done: rts
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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 ptr3
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stx ptr3+1 ; Save the passed em_copy pointer
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ldy #EM_COPY::OFFS
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lda (ptr3),y
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sta ptr1
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ldy #EM_COPY::PAGE
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lda (ptr3),y
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clc
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adc #>BASE
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sta ptr1+1 ; From
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ldy #EM_COPY::BUF
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lda (ptr3),y
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sta ptr2
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iny
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lda (ptr3),y
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sta ptr2+1 ; To
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common: ldy #EM_COPY::COUNT+1
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lda (ptr3),y ; Get number of pages
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beq @L2 ; Skip if no full pages
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sta tmp1
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; Copy full pages allowing interrupts after each page copied
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ldy #$00
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@L1: jsr transfer
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inc ptr1+1
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inc ptr2+1
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dec tmp1
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bne @L1
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; Copy the remainder of the page
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@L2: ldy #EM_COPY::COUNT
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lda (ptr3),y ; Get bytes in last page
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beq @L4
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tax
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; Transfer the bytes in the last page
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ldy #$00
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@L3: lda (ptr1),y
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sta (ptr2),y
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iny
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dex
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bne @L3
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; Done
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@L4: rts
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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 ptr3
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stx ptr3+1 ; Save the passed em_copy pointer
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ldy #EM_COPY::OFFS
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lda (ptr3),y
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sta ptr2
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ldy #EM_COPY::PAGE
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lda (ptr3),y
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clc
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adc #>BASE
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sta ptr2+1 ; To
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ldy #EM_COPY::BUF
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lda (ptr3),y
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sta ptr1
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iny
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lda (ptr3),y
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sta ptr1+1 ; From
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jmp common
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