# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1496523028 -7200
# Node ID 2d185cb3e4373abfe8f6b002e43635b10158b6dd
# Parent  b106107349679a1bf2805d3592138a89157a7573
Disable the line channel only when its completion is being handled.

diff -r b10610734967 -r 2d185cb3e437 vga.S
--- a/vga.S	Sat Jun 03 22:04:36 2017 +0200
+++ b/vga.S	Sat Jun 03 22:50:28 2017 +0200
@@ -876,12 +876,6 @@
 
 	la $s1, vfp_active
 
-	/* Disable the line channel. */
-
-	la $v0, DCH0ECON
-	li $v1, (1 << 4)
-	sw $v1, CLR($v0)
-
 _visible_active_ret:
 	jr $ra
 	nop
@@ -892,6 +886,23 @@
 
 visible_update_address:
 
+	/* Test for the last visible line. */
+
+	la $v0, vfp_active
+	bne $s1, $v0, _visible_update_address
+	nop
+
+	/* Disable the line channel. */
+
+	la $v0, DCH0ECON
+	li $v1, (1 << 4)
+	sw $v1, CLR($v0)
+
+	j _visible_update_ret
+	nop
+
+_visible_update_address:
+
 	/*
 	Update the line data address if the line counter (referring to the
 	next line) is even.