[U-Boot] [PATCH] ppc: Increase precision of ticks2usec

[U-Boot] [PATCH] ppc: Increase precision of ticks2usec

[Benoit Monin]

The tick of some PowerPC cpu is running at high frequency and
it can be used to get microsecond precision from it. Make use
of div64 to achieve this precision in ticks2usec.

Signed-off-by: Beno?t Monin <bmonin@adeneo.eu>
---
 lib_ppc/time.c |   15 +++++----------
 1 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/lib_ppc/time.c b/lib_ppc/time.c
index 173ffab..ebda13a 100644
--- a/lib_ppc/time.c
+++ b/lib_ppc/time.c
@@ -22,6 +22,7 @@
  */
 
 #include <common.h>
+#include <div64.h>
 
 #ifndef CONFIG_WD_PERIOD
 # define CONFIG_WD_PERIOD	(10 * 1000 * 1000)	/* 10 seconds default*/
@@ -71,17 +72,11 @@ void udelay(unsigned long usec)
 unsigned long ticks2usec(unsigned long ticks)
 {
 	ulong tbclk = get_tbclk();
+	u64 tmp;
 
-	/* usec = ticks * 1000000 / tbclk
-	 * Multiplication would overflow at ~4.2e3 ticks,
-	 * so we break it up into
-	 * usec = ( ( ticks * 1000) / tbclk ) * 1000;
-	 */
-	ticks *= 1000L;
-	ticks /= tbclk;
-	ticks *= 1000L;
-
-	return ((ulong)ticks);
+	tmp = ticks * 1000000ULL;
+	do_div (tmp, tbclk);
+	return (unsigned long)tmp;
 }
 #endif
 /* ------------------------------------------------------------------------- */
-- 


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[U-Boot] [PATCH] ppc: Increase precision of ticks2usec

[Wolfgang Denk]

Dear Benoit Monin,

In message <9454366.19868.1236182927234.JavaMail.www@wwinf8202> you wrote:
> 
> The tick of some PowerPC cpu is running at high frequency and
> it can be used to get microsecond precision from it. Make use
> of div64 to achieve this precision in ticks2usec.

Which problem are you trying to fix?

Where exactly do we need very high accuracy?

What is the overhead of using do_div() versus the old, simple code?

Best regards,

Wolfgang Denk

-- 
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Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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covered with dirt."                               - Blair P. Houghton

[U-Boot] [PATCH] ppc: Increase precision of ticks2usec

[Benoit Monin]

> De : "Wolfgang Denk"
> 
> Dear Benoit Monin,
> 
> In message <9454366.19868.1236182927234.JavaMail.www@wwinf8202> you wrote:
> > 
> > The tick of some PowerPC cpu is running at high frequency and
> > it can be used to get microsecond precision from it. Make use
> > of div64 to achieve this precision in ticks2usec.
> 
> Which problem are you trying to fix?
> 
> Where exactly do we need very high accuracy?
> 
> What is the overhead of using do_div() versus the old, simple code?
> 
Well, that was more some icing on the cake for CONFIG_PRINT_TIME,
so you can discard this patch.

> Best regards,
> 
> Wolfgang Denk
> 
Sincerely,
Beno?t.
--


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