# HG changeset patch
# User Laurens Holst <laurens.hg@grauw.nl>
# Date 1430768023 -7200
#      Mon May 04 21:33:43 2015 +0200
# Node ID 94a126e3f17817ed28aabc314c4ba125a39cb71b
# Parent  62ff055eb3038b7a4540d27005c3cabc9d7d63e7
System: Do not return values in the past from GetHighResTimerValue.

If an interrupt would occur between reading the timer LSB and MSB, it could
result in incorrect results. E.g. when the timer is 1FFH before the interrupt
and it is 280H after, the value returned would be 180H and time would run
backwards.

With this fix, if the MSB between two reads differs, it always returns 0 as the
LSB which must have been true somewhere between the MSB reads.

diff --git a/src/System.asm b/src/System.asm
--- a/src/System.asm
+++ b/src/System.asm
@@ -166,10 +166,11 @@
 	ld h,a
 	in a,(0E6H)
 	ld l,a
-	and a
-	ret m
 	in a,(0E7H)
+	cp h
+	ret z
 	ld h,a
+	ld l,0
 	ret
 
 System_Stop: