From 80873aa27c7a3eccbd3858fdd5c39925ea7a2fcf Mon Sep 17 00:00:00 2001
From: Leo C <erbl259-lmu@yahoo.de>
Date: Fri, 3 May 2019 21:27:50 +0200
Subject: [PATCH] simplify buffer level calculation

---
 cbios/ascii.180 | 13 +++++--------
 cbios/fifo.180  |  6 ++----
 2 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/cbios/ascii.180 b/cbios/ascii.180
index 9054549..d3f6b20 100644
--- a/cbios/ascii.180
+++ b/cbios/ascii.180
@@ -710,15 +710,12 @@ rxi_2:
 	and	b			;
 	ld	c,a
 
-	sub	(ix+o.out_idx)		;
-	jr	z,rxtxi&dev&_lp1	;skip if buffer is full
-
-	ld	(ix+o.in_idx),c		;input buffer pointer
-
-	jr	nc,$+3			;
-	 adc	b			;
+	sub	(ix+o.out_idx)		;number of free places in buffer
+	jr	z,rxtxi&dev&_lp1	;buffer full?
+	and	b			;
+	ld	(ix+o.in_idx),c		;  no, update input index
 
-	cp	s&dev&.tx_len*3/4
+	cp	s&dev&.tx_len*3/4	;buffer now 75% full?
 	jr	nz,rxtxi&dev&_lp1
 
    if dev=0				; only channel 0 has rts line
diff --git a/cbios/fifo.180 b/cbios/fifo.180
index e1bda54..ded979a 100644
--- a/cbios/fifo.180
+++ b/cbios/fifo.180
@@ -127,8 +127,7 @@ gech.wait:
 	halt
 	jr	gech.wait
 gech.cont:
-	jr	nc,$+5
-	 adc	(ix+o.mask)		; mask+carry == buffer size
+	and	(ix+o.mask)		;
 	dec	a
 	ld	b,a
 	ld	a,c
@@ -215,8 +214,7 @@ bph.wait:				; do
 ff_cnt:
 	ld	a,(ix+o.in_idx)		;
 	sub	(ix+o.out_idx)		;
-	ret	nc
-	adc	(ix+o.mask)		; mask+carry == buffer size
+	and	(ix+o.mask)		;
 	ret
 
 ;--------------------------------------------------------------
-- 
2.39.2