Re: [PATCH 24/56] microblaze_v2: time support

John Williams
2008-05-06T00:31:20Z

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Hi Michal,

On Mon, 2008-05-05 at 16:22 +0200, Michal Simek wrote:
> Hi John,
>
> you wrote me you have smarter implementation that xilinx did. Can you find it
> and send me it?

It's not much (any?) better? One less multiply I think? Attached
anyway - feel free to discard for now.

We could do a nice asm implementation with the optional mulhi
instruction, but that can wait.

Cheers,

John

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diff --git a/include/asm-microblaze/delay.h b/include/asm-microblaze/delay.h
index 481359c..e29a4de 100644
--- a/include/asm-microblaze/delay.h
+++ b/include/asm-microblaze/delay.h
@@ -2,32 +2,72 @@
* include/asm-microblaze/delay.h
*
* This file is subject to the terms and conditions of the GNU General Public
- * License. See the file "COPYING" in the main directory of this archive
+ * License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 2006 Atmark Techno, Inc.
*/

-#ifndef _ASM_MICROBLAZE_DELAY_H
-#define _ASM_MICROBLAZE_DELAY_H
+#ifndef _ASM_DELAY_H
+#define _ASM_DELAY_H

-#include <asm/param.h>
+#include <asm/param.h> /* For HZ */

-static inline void __delay(unsigned long loops)
+extern inline void __delay(unsigned long loops)
{
asm volatile ("# __delay \n\t" \
- "1: addi %0, %0, -1 \t\n" \
- "bneid %0, 1b \t\n" \
- "nop \t\n"
- : "=r" (loops)
- : "0" (loops));
+ "1: addi %0, %0, -1 \t\n" \
+ "bneid %0, 1b \t\n" \
+ "nop \t\n"
+ : "=r" (loops)
+ : "0" (loops));
}

-static inline void udelay(unsigned long usec)
+/*
+ * Note that 19 * 226 == 4294 ==~ 2^32 / 10^6, so
+ * loops = (4294 * usecs * loops_per_jiffy * HZ) / 2^32.
+ *
+ * The mul instruction gives us loops = (a * b) / 2^32.
+ * We choose a = usecs * 19 * HZ and b = loops_per_jiffy * 226
+ * because this lets us support a wide range of HZ and
+ * loops_per_jiffy values without either a or b overflowing 2^32.
+ * Thus we need usecs * HZ <= (2^32 - 1) / 19 = 226050910 and
+ * loops_per_jiffy <= (2^32 - 1) / 226 = 19004280
+ * (which corresponds to ~3800 bogomips at HZ = 100).
+ * -- paulus
+ */
+#define __MAX_UDELAY (226050910UL/HZ) /* maximum udelay argument */
+#define __MAX_NDELAY (4294967295UL/HZ) /* maximum ndelay argument */
+
+extern unsigned long loops_per_jiffy;
+
+extern __inline__ void __udelay(unsigned int x)
{
- unsigned long long tmp = usec;
- unsigned long loops = (tmp * 4295 * HZ * loops_per_jiffy) >> 32;
+ unsigned long long tmp=(unsigned long long)x*(unsigned long long)loops_per_jiffy*226LL;
+ unsigned loops=tmp>>32;
+
__delay(loops);
}

-#endif /* _ASM_MICROBLAZE_DELAY_H */
+extern __inline__ void __ndelay(unsigned int x)
+{
+ unsigned long long tmp=(unsigned long long)x*(unsigned long long)loops_per_jiffy*226LL;
+ unsigned loops=tmp>>32;
+
+ __delay(loops);
+}
+
+extern void __bad_udelay(void); /* deliberately undefined */
+extern void __bad_ndelay(void); /* deliberately undefined */
+
+#define udelay(n) (__builtin_constant_p(n)? \
+ ((n) > __MAX_UDELAY? __bad_udelay(): __udelay((n) * (19 * HZ))) : \
+ __udelay((n) * (19 * HZ)))
+
+#define ndelay(n) (__builtin_constant_p(n)? \
+ ((n) > __MAX_NDELAY? __bad_ndelay(): __ndelay((n) * HZ)) : \
+ __ndelay((n) * HZ))
+
+#define muldiv(a, b, c) (((a)*(b))/(c))
+
+#endif /* _ASM_DELAY_H */