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/*
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* Delay routines using pre computed loops_per_jiffy value.
*
* vineetg: Feb 2012
* -Rewrote in "C" to avoid dealing with availability of H/w MPY
* -Also reduced the num of MPY operations from 3 to 2
*
* Amit Bhor: Codito Technologies 2004
*/
#ifndef __ASM_ARC_UDELAY_H
#define __ASM_ARC_UDELAY_H
#include <asm/param.h> /* HZ */
static inline void __delay(unsigned long loops)
{
__asm__ __volatile__(
"1: sub.f %0, %0, 1 \n"
" jpnz 1b \n"
: "+r"(loops)
:
: "cc");
}
extern void __bad_udelay(void);
/*
* Normal Math for computing loops in "N" usecs
* -we have precomputed @loops_per_jiffy
* -1 sec has HZ jiffies
* loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
*
* Approximate Division by multiplication:
* -Mathematically if we multiply and divide a number by same value the
* result remains unchanged: In this case, we use 2^32
* -> (loops_per_N_usec * 2^32 ) / 2^32
* -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
* -> (loops_per_jiffy * HZ * N * 4295) / 2^32
*
* -Divide by 2^32 is very simply right shift by 32
* -We simply need to ensure that the multiply per above eqn happens in
* 64-bit precision (if CPU doesn't support it - gcc can emaulate it)
*/
static inline void __udelay(unsigned long usecs)
{
unsigned long loops;
/* (u64) cast ensures 64 bit MPY - real or emulated
* HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
*/
loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
__delay(loops);
}
#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
: __udelay(n)) : __udelay(n))
#endif /* __ASM_ARC_UDELAY_H */