[U-Boot] [PATCH] IXP425: Fixing timer code Part 1/1

[Stefan Althoefer]

[PATCH] IXP425: Fixing timer code

The non-interrupted timer code is inaccurate.

I found that the timing error of udelay() is caused by
to much looping overhead. The actual timing routine
was called repeatedly for each microsecond. When
I used bigger slices it became more accurate.

Some IXP425 ports have this line in their config file:

#define CONFIG_SYS_HZ   3333333    /* spec says 66.666 MHz,
                                but it appears to be 33 */

With this patch, this is nonsense. Instead you should use:

#ifdef CONFIG_USE_IRQ
/* Interrupt driven timer wants system tick here */
#define CONFIG_SYS_HZ                  1000
#else
/* The code in cpu/ixp/timer.c needs timer clock tick in HZ */
#define CONFIG_SYS_HZ                  66666666
#endif




The patch is against "latest" u-boot git-repository

Please (still) be patient if style of submission or patches are
offending.

Signed-off-by: Stefan Althoefer <stefan.althoefer at web.de>
----

diff -uprN u-boot-orig//cpu/ixp/timer.c u-boot/cpu/ixp/timer.c
--- u-boot-orig//cpu/ixp/timer.c	2008-12-02 17:25:31.000000000 +0100
+++ u-boot/cpu/ixp/timer.c	2008-12-02 22:27:22.000000000 +0100
@@ -46,6 +46,8 @@ void ixp425_udelay(unsigned long usec)
 	 */
 	unsigned long usecs = CONFIG_SYS_HZ/1000000L & ~IXP425_OST_RELOAD_MASK;
 
+	usecs *= usec;
+
 	*IXP425_OSST = IXP425_OSST_TIMER_1_PEND;
 	usecs |= IXP425_OST_ONE_SHOT | IXP425_OST_ENABLE;
 	*IXP425_OSRT1 = usecs;
@@ -54,7 +56,13 @@ void ixp425_udelay(unsigned long usec)
 
 void udelay (unsigned long usec)
 {
-	while (usec--) ixp425_udelay(1);
+	/* ipx425_udelay has big overhead, so call it in bigger slices */
+	while (usec>1000){
+		ixp425_udelay(1000);
+		usec -= 1000;
+	}
+	/* and now the rest */
+	ixp425_udelay(usec);
 }
 
 static ulong reload_constant = 0xfffffff0;