include/asm-nios2/tsc.h

   1 /*
   2  * Copyright (C) 2009 Philippe Gerum <rpm@xenomai.org>.
   3  *
   4  * Xenomai is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published
   6  * by the Free Software Foundation; either version 2 of the License,
   7  * or (at your option) any later version.
   8  *
   9  * Xenomai is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with Xenomai; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
  17  * 02111-1307, USA.
  18  */
  19
  20 #ifndef _XENO_ASM_NIOS2_TSC_H
  21 #define _XENO_ASM_NIOS2_TSC_H
  22
  23 #ifndef __KERNEL__
  24
  25 extern volatile void *xeno_nios2_hrclock;
  26
  27 static inline unsigned long long __xn_rdtsc(void)
  28 {
  29         volatile unsigned short *hrclock;
  30         int64_t t0, t1;
  31
  32         hrclock = xeno_nios2_hrclock;
  33
  34 #define hrclock_wrsnap(reg, val)                \
  35         (*(hrclock + (12 + ((reg) * 2)))) = (val)
  36
  37 #define hrclock_rdsnap(reg)                     \
  38         (int64_t)(*(hrclock + (12 + ((reg) * 2)))) << (reg * 16)
  39
  40 #define hrclock_peeksnap()                                              \
  41         ({                                                              \
  42                 int64_t __snap;                                         \
  43                 __snap = hrclock_rdsnap(3) | hrclock_rdsnap(2) |        \
  44                         hrclock_rdsnap(1) | hrclock_rdsnap(0);          \
  45                 __snap;                                                 \
  46         })
  47
  48 #define hrclock_getsnap()                                               \
  49         ({                                                              \
  50                 hrclock_wrsnap(0, 0);                                   \
  51                 hrclock_peeksnap();                                     \
  52         })
  53
  54         /*
  55          * We compete with both the kernel and userland applications
  56          * which may request a snapshot as well, but we don't have any
  57          * simple mutual exclusion mechanism at hand to avoid
  58          * races. In order to keep the overhead of reading the hrclock
  59          * from userland low, we make sure to read two consecutive
  60          * coherent snapshots. In case both readings do not match, we
  61          * have to request a fresh snapshot anew, since it means that
  62          * we have been preempted in the middle of the operation.
  63          */
  64         do {
  65                 t0 = hrclock_getsnap(); /* Request snapshot and read it */
  66                 __asm__ __volatile__("": : :"memory");
  67                 t1 = hrclock_peeksnap(); /* Confirm first reading */
  68         } while (t0 != t1);
  69
  70 #undef hrclock_getsnap
  71 #undef hrclock_rdsnap
  72 #undef hrclock_wrsnap
  73
  74         return ~t0;
  75 }
  76
  77 #endif /* __KERNEL__ */
  78
  79 #endif /* _XENO_ASM_NIOS2_TSC_H */