Re: [patch] Re: alpha - generic_init_pit - why using RTC for calibration?

["Oleg I. Vdovikin" <vdovikin@jscc.ru>]

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That's it.

Please also include my old rtc patch for 2.2.x series into official 2.2.20
kernel.

Thanks,
    Oleg.

-------------
From: "Jeff Garzik" <jgarzik@mandrakesoft.com>
Subject: Re: [patch] Re: alpha - generic_init_pit - why using RTC for
calibration?

> Oleg,
>
> The official kernel now carries Richard's version.  Can you post a diff
> on linux-kernel against version 2.4.7-pre2 perhaps, which cleans up
> Richard's code to yours?
> --
> Jeff Garzik      | Thalidomide, eh?
> Building 1024    | So you're saying the eggplant has an accomplice?
> MandrakeSoft     |
>

[-- Attachment #2: linux-2.2.x.rtc.patch --]
[-- Type: application/octet-stream, Size: 1972 bytes --]

--- linux/arch/alpha/kernel/time.c.orig	Mon Jul  2 14:05:09 2001
+++ linux/arch/alpha/kernel/time.c	Mon Jul  2 15:47:45 2001
@@ -231,6 +231,49 @@
 	outb(0x13, 0x42);
 }
 
+/*
+ * Calibrate CPU clock using legacy 8254 timer/counter. Stolen from
+ * arch/i386/time.c.
+ */
+
+#define CALIBRATE_DIVISOR	0xffff
+
+static unsigned long __init
+calibrate_cc(void)
+{
+	unsigned int cc;
+	unsigned long count = 0;
+	
+	/* Set the Gate high, disable speaker */
+	outb((inb(0x61) & ~0x02) | 0x01, 0x61);
+	
+	/*
+	 * Now let's take care of CTC channel 2
+	 *
+	 * Set the Gate high, program CTC channel 2 for mode 0,
+	 * (interrupt on terminal count mode), binary count,
+	 * load maximum divisor we can get for accuracy - 65535
+	 */
+	
+	outb(0xb0, 0x43);	/* binary, mode 0, LSB/MSB, Ch 2 */
+	outb(CALIBRATE_DIVISOR & 0xff, 0x42);	/* LSB of count */
+	outb(CALIBRATE_DIVISOR >> 8, 0x42);	/* MSB of count */
+
+	/* we still should not hang if timer not runing or N/A */
+	for (cc = rpcc(); (inb(0x61) & 0x20) == 0 && !(count >> 32); count++);
+
+	/* cycles delta */
+	cc = rpcc() - cc;
+	
+	/* check for the reliable result */
+	if ((count < 1) || (count >> 32))
+	    return 0;
+
+	/* and the final result in HZ */
+	return ((unsigned long)cc * CLOCK_TICK_RATE) / CALIBRATE_DIVISOR;
+}
+
+
 void
 time_init(void)
 {
@@ -239,6 +282,10 @@
 	unsigned long cycle_freq, ppm_error;
 	long diff;
 
+	/* Calibrate CPU clock using CTC. If this fails, use RTC. */
+	if (!est_cycle_freq)
+	    est_cycle_freq = calibrate_cc();
+
 	/*
 	 * The Linux interpretation of the CMOS clock register contents:
 	 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
@@ -275,7 +322,7 @@
 	if (diff < 0)
 		diff = -diff;
 	ppm_error = (diff * 1000000L) / cycle_freq;
-#if 0
+#if 1
 	printk("Alpha clock init: HWRPB %lu, Measured %lu, error=%lu ppm.\n",
 	       hwrpb->cycle_freq, est_cycle_freq, ppm_error);
 #endif

[-- Attachment #3: linux-2.4.7pre2.rtc.patch --]
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--- arch/alpha/kernel/time.c.orig	Thu Jul  5 12:18:48 2001
+++ arch/alpha/kernel/time.c	Thu Jul  5 12:24:11 2001
@@ -174,13 +174,12 @@
  * arch/i386/time.c.
  */
 
-#define CALIBRATE_LATCH	(52 * LATCH)
-#define CALIBRATE_TIME	(52 * 1000020 / HZ)
+#define CALIBRATE_LATCH	0xffff
 
 static unsigned long __init
 calibrate_cc_with_pic(void)
 {
-	int cc;
+	unsigned int cc;
 	unsigned long count = 0;
 
 	/* Set the Gate high, disable speaker */
@@ -191,39 +190,24 @@
 	 *
 	 * Set the Gate high, program CTC channel 2 for mode 0,
 	 * (interrupt on terminal count mode), binary count,
-	 * load 5 * LATCH count, (LSB and MSB) to begin countdown.
+	 * load maximum divisor we can get for accuracy - 65535
 	 */
 	outb(0xb0, 0x43);		/* binary, mode 0, LSB/MSB, Ch 2 */
 	outb(CALIBRATE_LATCH & 0xff, 0x42);	/* LSB of count */
 	outb(CALIBRATE_LATCH >> 8, 0x42);	/* MSB of count */
-
-	cc = rpcc();
-	do {
-		count++;
-	} while ((inb(0x61) & 0x20) == 0);
+	
+	/* we still should not hang if timer not runing or N/A */
+	for (cc = rpcc(); (inb(0x61) & 0x20) == 0 && !(count >> 32); count++);
+	
+	/* cycles delta */
 	cc = rpcc() - cc;
-
-	/* Error: ECTCNEVERSET */
-	if (count <= 1)
-		goto bad_ctc;
-
-	/* Error: ECPUTOOFAST */
-	if (count >> 32)
-		goto bad_ctc;
-
-	/* Error: ECPUTOOSLOW */
-	if (cc <= CALIBRATE_TIME)
-		goto bad_ctc;
-
-	return ((long)cc * 1000000) / CALIBRATE_TIME;
-
-	/*
-	 * The CTC wasn't reliable: we got a hit on the very first read,
-	 * or the CPU was so fast/slow that the quotient wouldn't fit in
-	 * 32 bits..
-	 */
- bad_ctc:
-	return 0;
+	
+	/* check for the reliable result */
+	if ((count < 1) || (count >> 32))
+		return 0;
+		
+	/* and the final result in HZ */
+	return ((unsigned long)cc * CLOCK_TICK_RATE) / CALIBRATE_LATCH;
 }
 
 /* The Linux interpretation of the CMOS clock register contents: