Add a time out table for delay requests.

We can pre-compute a table of suitable values in order to simplify the
run time random delay selection.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

makefile

@@ -25,7 +25,7 @@ LDFLAGS	=
 LDLIBS	= -lm -lrt
 PRG	= linuxptp
 OBJ	= bmc.o clock.o fsm.o linuxptp.o msg.o phc.o pi.o port.o print.o \
- servo.o transport.o udp.o util.o
+ servo.o tmtab.o transport.o udp.o util.o
 
 SRC	= $(OBJ:.o=.c)
 DEPEND	= $(OBJ:.o=.d)

tmtab.c

@@ -0,0 +1,54 @@
+/**
+ * @file tmtab.c
+ * @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.
+ */
+#include "tmtab.h"
+#include "tmv.h"
+
+void tmtab_init(struct tmtab *tt, int log_seconds)
+{
+	int i;
+	struct timespec incr, ts = {0, 0};
+	uint64_t max, min;
+
+	if (log_seconds < 0) {
+		log_seconds *= -1;
+		for (i = 1, max = 500000000ULL; i < log_seconds; i++) {
+			max >>= 1;
+		}
+	} else {
+		for (i = 0, max = 1000000000ULL; i < log_seconds; i++) {
+			max <<= 1;
+		}
+	}
+
+	min = max / (TMTAB_MAX - 1ULL);
+
+	incr.tv_sec = min / 1000000000ULL;
+	incr.tv_nsec = min % 1000000000ULL;
+
+	for (i = 0; i < TMTAB_MAX; i++) {
+		ts.tv_sec  += incr.tv_sec;
+		ts.tv_nsec += incr.tv_nsec;
+		while (ts.tv_nsec >= NS_PER_SEC) {
+			ts.tv_nsec -= NS_PER_SEC;
+			ts.tv_sec++;
+		}
+		tt->ts[i] = ts;
+	}
+}
+

tmtab.h

@@ -0,0 +1,56 @@
+/**
+ * @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