Index: rtc.c
===================================================================
--- rtc.c	(revision 280769)
+++ rtc.c	(working copy)
@@ -97,7 +97,7 @@
 static uint8_t rtc_nvram[RTC_NVRAM_SZ];
 
 /* XXX initialize these to default values as they would be from BIOS */
-static uint8_t status_a, status_b;
+static uint8_t status_a, status_b = RTCSB_24HR;
 
 static struct {
 	uint8_t  hours;
@@ -229,11 +229,25 @@
 			*eax = rtcout(tm.tm_min);
 			return (0);
 		case RTC_HRS:
-			if (status_b & RTCSB_24HR)
+			if (status_b & RTCSB_24HR) {
 				hour = tm.tm_hour;
-			else
-				hour = (tm.tm_hour % 12) + 1;
-			
+			} else {
+				switch (tm.tm_hour) {
+				case 0:			/* 12 AM */
+				case 12:		/* 12 PM */
+					hour = 12;
+					break;
+				default:
+					/*
+					 * The remaining tm_hour values
+					 * are interpreted as follows:
+					 * [1  - 11] -> 1 - 11 AM
+					 * [13 - 23] -> 1 - 11 PM
+					 */
+					hour = tm.tm_hour % 12;
+					break;
+				}
+			}
 			*eax = rtcout(hour);
 
 			/*