# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1510935766 -3600
# Node ID ff962c071724be815dd11aeb37afc5345881e955
# Parent  7edceda19310c46d591e96bec2eb73131b90079e
Update timer interrupt priorities atomically, removing disable/enable code.

diff -r 7edceda19310 -r ff962c071724 vga.S
--- a/vga.S	Thu Nov 16 23:59:56 2017 +0100
+++ b/vga.S	Fri Nov 17 17:22:46 2017 +0100
@@ -867,19 +867,12 @@
 	The condition still occurs, however.
 	*/
 
-	la $v0, IEC0
-	li $v1, (1 << 9)
-	sw $v1, CLR($v0)	/* T2IE = 0 */
-
 	la $v0, IPC2
-	li $v1, 0b11111
-	sw $v1, CLR($v0)	/* T2IP, T2IS = 0 */
-	li $v1, 0b00111
-	sw $v1, SET($v0)	/* T2IP = 1; T2IS = 3 */
-
-	la $v0, IEC0
-	li $v1, (1 << 9)
-	sw $v1, SET($v0)	/* T2IE = 0 */
+	lw $v1, 0($v0)
+	li $t8, ~0b11111
+	and $v1, $v1, $t8	/* T2IP = 0; T2IS = 0 */
+	ori $v1, $v1, 0b00111	/* T2IP = 1; T2IS = 3 */
+	sw $v1, 0($v0)
 
 	/* Enable the line channel for timer event transfer initiation. */
 
@@ -908,19 +901,12 @@
 
 	/* Restore delivery of the timer interrupt after the visible period. */
 
-	la $v0, IEC0
-	li $v1, (1 << 9)
-	sw $v1, CLR($v0)	/* T2IE = 0 */
-
 	la $v0, IPC2
-	li $v1, 0b11111
-	sw $v1, CLR($v0)	/* T2IP, T2IS = 0 */
-	li $v1, 0b11111
-	sw $v1, SET($v0)	/* T2IP = 7; T2IS = 3 */
-
-	la $v0, IEC0
-	li $v1, (1 << 9)
-	sw $v1, SET($v0)	/* T2IE = 1 */
+	lw $v1, 0($v0)
+	li $t8, ~0b11111
+	and $v1, $v1, $t8	/* T2IP = 0; T2IS = 0 */
+	ori $v1, $v1, 0b11111	/* T2IP = 7; T2IS = 3 */
+	sw $v1, 0($v0)
 
 	/* Disable the line channel. */