more work on SD card support

src/dos_m65/sdcard/sdcard_writesector.s

@@ -0,0 +1,78 @@
+
+;
+; Writes the sector to the SD card
+;
+
+; Based on https://github.com/MEGA65/mega65-libc/blob/master/cc65/src/sdcard.c
+
+
+; XXX finish, provide documentation
+
+
+sdcard_writesector:
+
+	; XXX check if card initialized and operable
+
+	lda SD_CTL
+	and #$03
+	bne sdcard_writesector             ; XXX add a timer here
+
+	; End reset
+
+	lda #$01
+	sta SD_CTL
+
+	; Set write address
+
+	jsr sdcard_set_addr
+
+
+
+
+
+
+
+	jsr sdcard_writesector_copy_data
+
+
+
+
+
+
+
+
+
+
+;
+; Helper routines
+;
+
+sdcard_writesector_copy_data:
+
+	; XXX use DMAgic for this
+
+	phz
+	phx
+
+	ldx #$00
+	ldz #$00
+
+@1:
+	lda CARD_BUF,x
+	sta [CARD_BUFPNT],z
+	inc CARD_BUFPNT+1
+	lda CARD_BUF+$100,x
+	sta [CARD_BUFPNT],z
+	dec CARD_BUFPNT+1	
+
+	inz
+	inx
+	bne @1
+
+	; Restore registers and quit
+
+	plx
+	plz
+
+	clc
+	rts