fix duration reading code

messages.asm

@@ -162,7 +162,12 @@ beep:
 	mov ah, 0x00	; read keypress
 	int 0x16
 	;; Read ASCII character is in al
-	sub al, 'a' 	; normalise (a=0, b=1, c=...)
+	;; the character must be normalised to a=1, b=2, ...
+	;; and not a=0, b=1, ... because during the waiting loop
+	;; see #NOTE_LOOP
+	;; the duration counter gets decremented BEFORE
+	;; it gets compared to zero
+	sub al, 'b' 	; normalise (a=1, b=2, c=...)
 
 	;; interrupt 0x16, ah=0 returns the read scancode in ah
 	;; so ah must be reset
@@ -207,6 +212,9 @@ beep:
 	dec     cx	; count down
 	jne     .pause2	; if not zero keep counting down
 
+	;; #NOTE_LOOP
+	;; the duration gets decremented before being checked
+	;; hence why it was normalised to 'b' and not 'a'
 	dec     ax	; decrement duration counter
 	jne     .pause1	; keep doing that until it is 0