2 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
8 * Delay routines using pre computed loops_per_jiffy value.
11 * -Rewrote in "C" to avoid dealing with availability of H/w MPY
12 * -Also reduced the num of MPY operations from 3 to 2
14 * Amit Bhor: Codito Technologies 2004
17 #ifndef __ASM_ARC_UDELAY_H
18 #define __ASM_ARC_UDELAY_H
20 #include <asm-generic/types.h>
21 #include <asm/param.h> /* HZ */
23 extern unsigned long loops_per_jiffy
;
25 static inline void __delay(unsigned long loops
)
28 " mov lp_count, %0 \n"
37 extern void __bad_udelay(void);
40 * Normal Math for computing loops in "N" usecs
41 * -we have precomputed @loops_per_jiffy
42 * -1 sec has HZ jiffies
43 * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
45 * Approximate Division by multiplication:
46 * -Mathematically if we multiply and divide a number by same value the
47 * result remains unchanged: In this case, we use 2^32
48 * -> (loops_per_N_usec * 2^32 ) / 2^32
49 * -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
50 * -> (loops_per_jiffy * HZ * N * 4295) / 2^32
52 * -Divide by 2^32 is very simply right shift by 32
53 * -We simply need to ensure that the multiply per above eqn happens in
54 * 64-bit precision (if CPU doesn't support it - gcc can emaulate it)
57 static inline void __udelay(unsigned long usecs
)
61 /* (u64) cast ensures 64 bit MPY - real or emulated
62 * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
64 loops
= ((u64
) usecs
* 4295 * HZ
* loops_per_jiffy
) >> 32;
69 #define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
70 : __udelay(n)) : __udelay(n))
72 #endif /* __ASM_ARC_UDELAY_H */