2 ; Extended memory driver for the VDC RAM available on all C128 machines
3 ; (based on code by Ullrich von Bassewitz)
4 ; Maciej 'YTM/Elysium' Witkowiak <ytm@elysium.pl>
7 .include "zeropage.inc"
9 .include "em-kernel.inc"
10 .include "em-error.inc"
16 ; ------------------------------------------------------------------------
17 ; Header. Includes jump table
19 module_header _c128_vdc_emd
23 .byte $65, $6d, $64 ; "emd"
24 .byte EMD_API_VERSION ; EM API version number
41 ; ------------------------------------------------------------------------
44 VDC_ADDR_REG = $D600 ; VDC address
45 VDC_DATA_REG = $D601 ; VDC data
47 VDC_DATA_HI = 18 ; used registers
52 ; ------------------------------------------------------------------------
57 pagecount: .word 64 ; $0000-$3fff as 16k default
58 curpage: .word $ffff ; currently mapped-in page (invalid)
62 window: .res 256 ; memory window
66 ; ------------------------------------------------------------------------
67 ; INSTALL routine. Is called after the driver is loaded into memory. If
68 ; possible, check if the hardware is present and determine the amount of
70 ; Must return an EM_ERR_xx code in a/x.
74 ; do test for VDC presence here???
76 ldx #VDC_CSET ; determine size of RAM...
80 jsr vdcputreg ; turn on 64k
82 jsr settestadr1 ; save original value of test byte
86 lda #$55 ; write $55 here
88 jsr test64k ; read it here and there
89 lda #$aa ; write $aa here
91 jsr test64k ; read it here and there
95 jsr vdcputbyte ; restore original value of test byte
97 lda ptr1 ; do bytes match?
106 jsr vdcputreg ; restore 16/64k flag
107 jmp @endok ; and leave default values for 16k
126 jsr vdcputbyte ; write $55
128 jsr vdcgetbyte ; read here
131 jsr vdcgetbyte ; and there
140 ldy #$02 ; test page 2 (here)
143 ldy #$42 ; or page 64+2 (there)
147 ; ------------------------------------------------------------------------
148 ; UNINSTALL routine. Is called before the driver is removed from memory.
149 ; Can do cleanup or whatever. Must not return anything.
153 ;on C128 restore font and clear the screen?
156 ; ------------------------------------------------------------------------
157 ; PAGECOUNT: Return the total number of available pages in a/x.
165 ; ------------------------------------------------------------------------
166 ; MAP: Map the page in a/x into memory and return a pointer to the page in
167 ; a/x. The contents of the currently mapped page (if any) may be discarded
188 ; copy a single page from (ptr1):VDCRAM to (ptr2):RAM
193 jsr vdcsetsrcaddr ; set source address in VDC
197 @L0: bit VDC_ADDR_REG
199 lda VDC_DATA_REG ; get 2 bytes at a time to speed-up
200 sta (ptr2),y ; (in fact up to 8 bytes could be fetched with special VDC config)
208 ; ------------------------------------------------------------------------
209 ; USE: Tell the driver that the window is now associated with a given page.
212 stx curpage+1 ; Remember the page
214 ldx #>window ; Return the window
217 ; ------------------------------------------------------------------------
218 ; COMMIT: Commit changes in the memory window to extended storage.
221 lda curpage ; jump if no page mapped
233 ; fall through to transferout
235 ; copy a single page from (ptr2):RAM to (ptr1):VDCRAM
240 jsr vdcsetsrcaddr ; set source address in VDC
244 @L0: bit VDC_ADDR_REG
246 lda (ptr2),y ; speedup does not work for writing
252 ; ------------------------------------------------------------------------
253 ; COPYFROM: Copy from extended into linear memory. A pointer to a structure
254 ; describing the request is passed in a/x.
255 ; The function must not return anything.
260 beq @L2 ; Skip if no full pages
270 ; Copy the remainder of the page
272 @L2: ldy #EM_COPY::COUNT
273 lda (ptr3),y ; Get bytes in last page
277 ; Transfer the bytes in the last page
288 ; ------------------------------------------------------------------------
289 ; COPYTO: Copy from linear into extended memory. A pointer to a structure
290 ; describing the request is passed in a/x.
291 ; The function must not return anything.
296 beq @L2 ; Skip if no full pages
306 ; Copy the remainder of the page
308 @L2: ldy #EM_COPY::COUNT
309 lda (ptr3),y ; Get bytes in last page
313 ; Transfer the bytes in the last page
324 ;-------------------------------------------------------------------------
325 ; Helper functions to handle VDC ram
331 @L0: bit VDC_ADDR_REG
344 @L0: bit VDC_ADDR_REG
353 @L0: bit VDC_ADDR_REG
358 ; ------------------------------------------------------------------------
359 ; Helper function for COPYFROM and COPYTO: Store the pointer to the request
360 ; structure and prepare data for the copy
365 stx ptr3+1 ; Save the passed em_copy pointer
381 ldy #EM_COPY::COUNT+1
382 lda (ptr3),y ; Get number of pages