linuxptp/tmtab.h

57 lines
1.7 KiB
C

/**
* @file tmtab.h
* @brief Implements a table of time out values.
* @note Copyright (C) 2011 Richard Cochran <richardcochran@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifndef HAVE_TMTAB_H
#define HAVE_TMTAB_H
#include <time.h>
/*
* Let 'D' be the logMinDelayReqInterval
* and 'S' be the logSyncInterval.
*
* The delay request interval ranges from zero to 2^{D+1} seconds.
* The standard requires that
*
* S <= D <= S+5
*
* and the timeout granularity not more than 2^{S-4} seconds.
* Thus, the minimum required number of grains is given by
*
* 2^{D+1} / 2^{S-4} = 2^{D-S+5}
*
* and finds a minimum of 2^5 and a maximum of 2^10.
*
* The timeout table allows for the maximum number of grains required.
*
* Note that the table is made to be biased so that when sampling the
* table randomly, the average delay value will be slightly larger
* than logMinDelayReqInterval, in order to satisfy the wording of the
* standard.
*/
#define TMTAB_MAX 1024
struct tmtab {
struct timespec ts[TMTAB_MAX];
};
void tmtab_init(struct tmtab *tt, int log_seconds);
#endif