/* * 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-generic/types.h> #include <asm/param.h> /* HZ */ extern unsigned long loops_per_jiffy; static inline void __delay(unsigned long loops) { __asm__ __volatile__( " mov lp_count, %0 \n" " lp 1f \n" " nop \n" "1: \n" : : "r"(loops) : "lp_count"); } 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 */