--- /dev/null
+;
+; Extended memory driver for the Commodore REU
+;
+; Ullrich von Bassewitz, 2002-11-29
+;
+
+ .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 $00 ; EM API version number
+
+; Jump table.
+
+ .word INSTALL
+ .word DEINSTALL
+ .word PAGECOUNT
+ .word MAP
+ .word MAPCLEAN
+ .word COPYFROM
+ .word COPYTO
+
+; ------------------------------------------------------------------------
+; Constants
+
+REU_STATUS = $DF00 ; Status register
+REU_COMMAND = $DF01 ; Command register
+REU_C64ADDR = $DF02 ; C64 base address register
+REU_REUADDR = $DF04 ; REU base address register
+REU_COUNT = $DF07 ; Transfer count register
+REU_IRQMASK = $DF09 ; IRQ mask register
+REU_CONTROL = $DF0A ; Control register
+
+OP_COPYFROM = $ED
+OP_COPYTO = $EC
+
+
+; ------------------------------------------------------------------------
+; Data.
+
+.data
+pagecount: .res 2 ; Number of pages available
+curpage: .word $FFFF ; Current page number (invalid)
+
+.bss
+window: .res 256 ; Memory "window"
+
+reu_params: .word $0000 ; Host address, lo, hi
+ .word $0000 ; Exp address, lo, hi
+ .byte $00 ; Expansion bank no.
+ .word $0000 ; # bytes to move, lo, hi
+ .byte $00 ; Interrupt mask reg.
+ .byte $00 ; Adress control reg.
+
+
+
+.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 #$55
+ sta REU_REUADDR
+ cmp REU_REUADDR ; Check for presence of REU
+ bne nodevice
+ lda #$AA
+ sta REU_REUADDR
+ cmp REU_REUADDR ; Check for presence of REU
+ bne nodevice
+
+ ldx #>(128*4) ; Assume 128KB
+ lda REU_STATUS
+ and #$10 ; Check size bit
+ beq @L1
+ ldx #>(256*4) ; 256KB when size bit is set
+@L1: stx pagecount+1
+
+ lda #<EM_ERR_OK
+ ldx #>EM_ERR_OK
+ rts
+
+; No REU found
+
+nodevice:
+ lda #<EM_ERR_NO_DEVICE
+ ldx #>EM_ERR_NO_DEVICE
+ rts
+
+; ------------------------------------------------------------------------
+; DEINSTALL routine. Is called before the driver is removed from memory.
+; Can do cleanup or whatever. Must not return anything.
+;
+
+DEINSTALL:
+ 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) are assumed to be
+; dirty and must be saved into secondary storage if this is necessary.
+;
+
+MAP: ldy curpage+1 ; Do we have a page mapped?
+ bmi MAPCLEAN ; Jump if no page mapped
+
+ ldy #<window
+ sty REU_C64ADDR
+ ldy #>window
+ sty REU_C64ADDR+1
+
+ ldy #0
+ sty REU_COUNT+0
+ sty REU_REUADDR+0
+ ldy curpage
+ sty REU_REUADDR+1
+ ldy curpage+1
+ sty REU_REUADDR+2
+
+ ldy #1
+ sty REU_COUNT+1 ; Move 256 bytes
+ ldy #OP_COPYTO
+ pha
+ jsr Transfer ; Transfer 256 bytes into REU
+ pla
+
+; Run straight into MAPCLEAN
+
+; ------------------------------------------------------------------------
+; MAPCLEAN: 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) are assumed to
+; be clean, so if this is an advantage for the driver, the current contents
+; may be discarded.
+
+MAPCLEAN:
+ sta curpage
+ stx curpage+1 ; Remember the new page
+
+ ldy #<window
+ sty REU_C64ADDR
+ ldy #>window
+ sty REU_C64ADDR+1
+
+ ldy #0
+ sty REU_COUNT+0
+ sty REU_REUADDR+0
+ sta REU_REUADDR+1
+ stx REU_REUADDR+2
+
+ ldy #1
+ sty REU_COUNT+1 ; Move 256 bytes
+ ldy #OP_COPYFROM
+ jsr Transfer ; Transfer 256 bytes into REU
+
+ lda #<window
+ ldx #>window ; Return the window address
+ 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:
+
+
+; ------------------------------------------------------------------------
+; 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:
+ lda #0
+ tax
+ rts
+
+; ---------------------------------------------------------------------------
+; Transfer subroutine for the REU. Expects command in Y.
+
+Transfer:
+ sty $df01 ; Issue command
+
+ sei ; Save the value of the
+ ldy $01 ; the c64 control port
+ tya ; and turn on lower 3 bits
+ ora #$03 ; to bank out ROMs, I/O.
+ sta $01
+ lda $ff00
+ sta $ff00 ; Now start transfer...
+
+ sty $01 ; Restore the old configuration
+ cli
+ rts
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