peasant: drive2: work on drive2 support

games/peasant/drive2.s

@@ -0,0 +1,61 @@
+; based on anti-m/anti-m.a
+
+check_floppy_in_drive2:
+
+	lda	$C0EB		;	drive 2 select
+
+	jsr	driveon
+
+;	lda	$C0E9		;	motor on	1110 1001
+
+;	jsr	spinup		; spin up drive
+
+	jsr	seek		; seek to where?
+
+
+	;=====================================
+	; try 768 times to find valid sector
+
+	; does this by looking for $D5 $AA $96 sector address header
+
+	ldx	#2
+	ldy	#0
+
+check_drive2_loop:
+	iny
+	bne	keep_trying
+
+	;========================
+	; didn't find it in time
+
+	clc				; clear Carry for failure
+	dex
+	bmi	done_check		; actually done after 3*256
+
+keep_trying:
+
+get_valid_byte:
+	lda	$C0EC			; read byte
+	bpl	get_valid_byte		; keep trying if high bit not set
+
+check_if_d5:
+	cmp	#$D5			; see if D5 (start of ... )
+	bne	check_drive2_loop	; if not, try again
+
+check_if_aa:
+	lda	$C0EC			; read byte
+	bpl	check_if_aa		; keep trying until valid
+	cmp	#$AA			; see if aa
+	bne 	get_valid_byte		; if not try again
+
+check_if_96:
+	lda	$C0EC			; read byte
+	bpl	check_if_96		; keep trying until valid
+	cmp	#$96			; see if 96
+	bne	check_if_d5		; if not try again
+
+	; if we make it here, carry is set
+	; because result was greater or equal to #$96
+
+done_check:
+	jmp	driveoff