headers/private/system/arch/ppc/arch_real_time_data.h

   1 /*
   2  * Copyright 2006, Ingo Weinhold <bonefish@cs.tu-berlin.de>.
   3  * All rights reserved. Distributed under the terms of the MIT License.
   4  */
   5 #ifndef _KERNEL_ARCH_REAL_TIME_DATA_H
   6 #define _KERNEL_ARCH_REAL_TIME_DATA_H
   7
   8 #include <StorageDefs.h>
   9 #include <SupportDefs.h>
  10
  11
  12 struct ppc_real_time_data {
  13         vint64  system_time_offset;
  14 };
  15
  16 struct arch_real_time_data {
  17         struct ppc_real_time_data       data[2];
  18         vint32                                          system_time_conversion_factor;
  19         vint32                                          version;
  20                 // Since there're no cheap atomic_{set,get,add}64() on PPC 32 (i.e. one
  21                 // that doesn't involve a syscall), we can't have just a single
  22                 // system_time_offset and set/get it atomically.
  23                 // That's why have our data twice. One set is current (indexed by
  24                 // version % 2). When setting the offset, we do that with disabled
  25                 // interrupts and protected by a spinlock. We write the new values
  26                 // into the other array element and increment the version.
  27                 // A reader first reads the version, then the date of interest, and
  28                 // finally rechecks the version. If it hasn't changed in the meantime,
  29                 // the read value is fine, otherwise it runs the whole procedure again.
  30                 //
  31                 // system_time_conversion_factor is currently consider constant,
  32                 // although that is not necessarily true. We simply don't support
  33                 // changing conversion factors at the moment.
  34 };
  35
  36 #endif  /* _KERNEL_ARCH_REAL_TIME_DATA_H */