2 ; Extended memory driver for the VIC20 $A000-$BFFF RAM. Driver works without
3 ; problems when statically linked.
5 ; Marco van den Heuvel, 2018-03-16
8 .include "zeropage.inc"
10 .include "em-kernel.inc"
11 .include "em-error.inc"
18 ; ------------------------------------------------------------------------
19 ; Header. Includes jump table
21 module_header _vic20_rama_emd
25 .byte $65, $6d, $64 ; "emd"
26 .byte EMD_API_VERSION ; EM API version number
43 ; ------------------------------------------------------------------------
47 PAGES = ($C000 - BASE) / 256
49 ; ------------------------------------------------------------------------
53 curpage: .res 1 ; Current page number
54 window: .res 256 ; Memory "window"
58 ; ------------------------------------------------------------------------
59 ; INSTALL routine. Is called after the driver is loaded into memory. If
60 ; possible, check if the hardware is present and determine the amount of
62 ; Must return an EM_ERR_xx code in a/x.
66 lda $A000 ; see what is at address $A000
67 inc $A000 ; see if it can be changed
68 cmp $A000 ; did it stick ?
73 stx curpage ; Invalidate the current page
75 txa ; A = X = EM_ERR_OK
78 nomem: ldx #>EM_ERR_NO_DEVICE
79 lda #<EM_ERR_NO_DEVICE
80 ; rts ; Run into UNINSTALL instead
82 ; ------------------------------------------------------------------------
83 ; UNINSTALL routine. Is called before the driver is removed from memory.
84 ; Can do cleanup or whatever. Must not return anything.
91 ; ------------------------------------------------------------------------
92 ; PAGECOUNT: Return the total number of available pages in a/x.
100 ; ------------------------------------------------------------------------
101 ; MAP: Map the page in a/x into memory and return a pointer to the page in
102 ; a/x. The contents of the currently mapped page (if any) may be discarded
106 MAP: sta curpage ; Remember the new page
121 jsr transfer ; Transfer one page
123 ; Return the memory window
126 ldx #>window ; Return the window address
129 ; ------------------------------------------------------------------------
130 ; USE: Tell the driver that the window is now associated with a given page.
132 USE: sta curpage ; Remember the page
134 ldx #>window ; Return the window
137 ; ------------------------------------------------------------------------
138 ; COMMIT: Commit changes in the memory window to extended storage.
140 COMMIT: lda curpage ; Get the current page
141 bmi done ; Jump if no page mapped
154 ; Transfer one page. Y must be zero on entry
158 ; Unroll the following loop
172 ; ------------------------------------------------------------------------
173 ; COPYFROM: Copy from extended into linear memory. A pointer to a structure
174 ; describing the request is passed in a/x.
175 ; The function must not return anything.
180 stx ptr3+1 ; Save the passed em_copy pointer
198 common: ldy #EM_COPY::COUNT+1
199 lda (ptr3),y ; Get number of pages
200 beq @L2 ; Skip if no full pages
203 ; Copy full pages allowing interrupts after each page copied
212 ; Copy the remainder of the page
214 @L2: ldy #EM_COPY::COUNT
215 lda (ptr3),y ; Get bytes in last page
219 ; Transfer the bytes in the last page
232 ; ------------------------------------------------------------------------
233 ; COPYTO: Copy from linear into extended memory. A pointer to a structure
234 ; describing the request is passed in a/x.
235 ; The function must not return anything.
239 stx ptr3+1 ; Save the passed em_copy pointer