i386/113540: decrease i8254 calibration precision to make it work with Xbox, remove warnings

[Ed Schouten]

>Number:         113540
>Category:       i386
>Synopsis:       decrease i8254 calibration precision to make it work with Xbox, remove warnings
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Jun 10 20:20:02 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Ed Schouten
>Release:        FreeBSD 6.2-STABLE i386
>Organization:
>Environment:
System: FreeBSD palm.hoeg.nl 6.2-STABLE FreeBSD 6.2-STABLE #0: Fri Apr 20 13:44:49 CEST 2007 root at palm.hoeg.nl:/usr/obj/usr/src/sys/PALM i386
>Description:
For some reason, the timers in the Microsoft Xbox aren't as sane as on
PC's; it has two issues:

- The frequency of the i8254 timer is 1125000 Hz instead of 1193182 Hz.
  The Microsoft Xbox port currently solves this by hardcoding TIMER_FREQ
  in the config file.
- The diagnostic and status registers of the RTC contain invalid data,
  which causes FreeBSD to assume the RTC is broken. This causes a lot of
  spurious messages in the dmesg.
>How-To-Repeat:
>Fix:
I've been using the following patch on my Xbox for a long time now; it
essentially does the following things:

- It changes the rtcin() routine to return fake values for the diagnose
  and status registers, which forces FreeBSD to properly use theh RTC.
- It decreases the precision of the timer (by default disabled) timer
  calibration code from 1% to 10%; this is needed because the Xbox clock
  is 6% off.
- It removes the hardcoded Xbox timer value from the Xbox configuration
  file and enables timer calibration.

The reason why we want to do such a thing is because we could then
compile kernels that run on Xbox'es and PC's without a clock drift on
one of those systems.

--- src/sys/i386/isa/clock.c	Tue Jan 23 19:18:32 2007
+++ src/sys/i386/isa/clock.c	Thu Feb  8 18:07:28 2007
@@ -94,6 +94,10 @@
 #include <i386/bios/mca_machdep.h>
 #endif
 
+#ifdef XBOX
+#include <machine/xbox.h>
+#endif
+
 #define	TIMER_DIV(x) ((timer_freq + (x) / 2) / (x))
 
 int	clkintr_pending;
@@ -421,6 +425,23 @@
 {
 	u_char val;
 
+#ifdef XBOX
+	/*
+	 * The RTC in the Microsoft Xbox always reports errors,
+	 * including power problems, though it's functioning correctly.
+	 * We want to use the RTC to calibrate the timer, because its
+	 * frequency isn't the same as a regular PC.
+	 */
+	if (arch_i386_is_xbox) {
+		switch (reg) {
+		case RTC_DIAG:
+			return (0);
+		case RTC_STATUSD:
+			return (RTCSD_PWR);
+		}
+	}
+#endif
+
 	RTC_LOCK;
 	if (rtc_reg != reg) {
 		inb(0x84);
@@ -631,7 +652,7 @@
 	 * frequency.
 	 */
 	delta = freq > timer_freq ? freq - timer_freq : timer_freq - freq;
-	if (delta < timer_freq / 100) {
+	if (delta < timer_freq / 10) {
 #ifndef CLK_USE_I8254_CALIBRATION
 		if (bootverbose)
 			printf(
@@ -642,7 +663,7 @@
 	} else {
 		if (bootverbose)
 			printf(
-		    "%d Hz differs from default of %d Hz by more than 1%%\n",
+		    "%d Hz differs from default of %d Hz by more than 10%%\n",
 			       freq, timer_freq);
 	}
 
--- src/sys/i386/conf/XBOX	Mon Feb  5 16:50:16 2007
+++ src/sys/i386/conf/XBOX	Mon Feb  5 17:36:12 2007
@@ -42,8 +42,7 @@
 #options 	_KPOSIX_PRIORITY_SCHEDULING # POSIX P1003_1B real-time extensions
 #options 	KBD_INSTALL_CDEV	# install a CDEV entry in /dev
 options 	ADAPTIVE_GIANT		# Giant mutex is adaptive.
-# Xbox has a non-standard default timer frequency
-options 	TIMER_FREQ=1125000	# Gives ~733.34MHz CPU
+options 	CLK_USE_I8254_CALIBRATION # Timer has non-standard frequency
 
 #device		apic			# I/O APIC
 
>Release-Note:
>Audit-Trail:
>Unformatted: