; Extended Memory Driver for the Kerberos MIDI interface. ; http://www.frank-buss.de/kerberos/ ; based on the code for RamCart 64/128KB cartridge. ; 2020-06-16 Dirk Jagdmann .include "zeropage.inc" .include "em-kernel.inc" .include "em-error.inc" .macpack generic .macpack module ; ------------------------------------------------------------------------ ; Header. Includes jump table module_header _c64_kerberos_emd ; Driver signature .byte $65, $6d, $64 ; "emd" .byte EMD_API_VERSION ; EM API version number ; Library reference .addr $0000 ; Jump table .addr INSTALL .addr UNINSTALL .addr PAGECOUNT .addr MAP .addr USE .addr COMMIT .addr COPYFROM .addr COPYTO ; ------------------------------------------------------------------------ ; Constants RAMC_WINDOW = $DF00 ; Address of Kerberos SRAM RAMC_PAGE_LO = $DE3E ; Page register low RAMC_PAGE_HI = $DE3F ; Page register high .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: ;; write $55 into first page lda #0 sta RAMC_PAGE_LO sta RAMC_PAGE_HI lda #$55 sta RAMC_WINDOW ;; write $AA into second page lda #1 sta RAMC_PAGE_LO sta RAMC_PAGE_HI lda #$AA sta RAMC_WINDOW ;; check $55 in first page lda #0 sta RAMC_PAGE_LO sta RAMC_PAGE_HI lda RAMC_WINDOW cmp #$55 bne @notpresent ;; check $AA in first page lda #1 sta RAMC_PAGE_LO sta RAMC_PAGE_HI lda RAMC_WINDOW cmp #$AA bne @notpresent lda #EM_ERR_OK .assert EM_ERR_OK = 0, error tax rts @notpresent: lda #EM_ERR_NO_DEVICE ldx #0 ; return value is char ; use rts from UNINSTALL below ; ------------------------------------------------------------------------ ; UNINSTALL routine. Is called before the driver is removed from memory. ; Can do cleanup or whatever. Must not return anything. ; UNINSTALL: rts ; ------------------------------------------------------------------------ ; PAGECOUNT: Return the total number of available pages in a/x. ; PAGECOUNT: lda #<(128 * 1024 / 256) ldx #>(128 * 1024 / 256) rts ; ------------------------------------------------------------------------ ; USE: Tell the driver that the window is now associated with a given page. ; The Kerberos cartridge does not copy but actually map the window, so USE is ; identical to MAP. USE = MAP ; ------------------------------------------------------------------------ ; 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) may be discarded ; by the driver. ; MAP: sta RAMC_PAGE_LO txa and #1 sta RAMC_PAGE_HI lda #RAMC_WINDOW ; Use the RTS from COMMIT below to save a precious byte of storage ; ------------------------------------------------------------------------ ; COMMIT: Commit changes in the memory window to extended storage. COMMIT: 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: jsr setup ; Setup is: ; ; - ptr1 contains the struct pointer ; - ptr2 contains the linear memory buffer ; - ptr3 contains -(count-1) ; - tmp1 contains the low page register value ; - tmp2 contains the high page register value ; - X contains the page offset ; - Y contains zero beq @L5 ; will always branch, because setup ends with ldy #0 @L1: lda RAMC_WINDOW,x sta (ptr2),y iny bne @L2 inc ptr2+1 @L2: inx beq @L4 ; Bump count and repeat @L3: inc ptr3 bne @L1 inc ptr3+1 bne @L1 rts ; Bump page register @L4: inc tmp1 bne @L5 inc tmp2 @L5: lda tmp1 sta RAMC_PAGE_LO lda tmp2 sta RAMC_PAGE_HI jmp @L3 ; ------------------------------------------------------------------------ ; 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: jsr setup ; Setup is: ; ; - ptr1 contains the struct pointer ; - ptr2 contains the linear memory buffer ; - ptr3 contains -(count-1) ; - tmp1 contains the low page register value ; - tmp2 contains the high page register value ; - X contains the page offset ; - Y contains zero beq @L5 ; will always branch, because setup ends with ldy #0 @L1: lda (ptr2),y sta RAMC_WINDOW,x iny bne @L2 inc ptr2+1 @L2: inx beq @L4 ; Bump count and repeat @L3: inc ptr3 bne @L1 inc ptr3+1 bne @L1 rts ; Bump page register @L4: inc tmp1 bne @L5 inc tmp2 @L5: lda tmp1 sta RAMC_PAGE_LO lda tmp2 sta RAMC_PAGE_HI jmp @L3 ; ------------------------------------------------------------------------ ; Helper function for COPYFROM and COPYTO: Store the pointer to the request ; structure and prepare data for the copy setup: sta ptr1 stx ptr1+1 ; Save passed pointer ; Get the page number from the struct and adjust it so that it may be used ; with the hardware. That is: lower 6 bits in tmp1, high bits in tmp2. ldy #EM_COPY::PAGE+1 lda (ptr1),y sta tmp2 dey lda (ptr1),y sta tmp1 ; Get the buffer pointer into ptr2 ldy #EM_COPY::BUF lda (ptr1),y sta ptr2 iny lda (ptr1),y sta ptr2+1 ; Get the count, calculate -(count-1) and store it into ptr3 ldy #EM_COPY::COUNT lda (ptr1),y eor #$FF sta ptr3 iny lda (ptr1),y eor #$FF sta ptr3+1 ; Get the page offset into X and clear Y ldy #EM_COPY::OFFS lda (ptr1),y tax ldy #$00 ; Done rts