X-Git-Url: http://git.efficios.com/?p=ctf.git;a=blobdiff_plain;f=common-trace-format-specification.txt;h=528029dc9d4ce799f394cf5105e159d1201869ac;hp=e8c9e48f6d87145e20a4c4af7a7bf5cc6cedc729;hb=d803bfcbf48cebc1fe31336930f674408dfce651;hpb=ed1a0b45aaa8184cb1d9aa18d5a205a862fbf446

diff --git a/common-trace-format-specification.txt b/common-trace-format-specification.txt
index e8c9e48..528029d 100644
--- a/common-trace-format-specification.txt
+++ b/common-trace-format-specification.txt
@@ -65,6 +65,7 @@ Table of Contents
        7.3.1 Lexical Scope
        7.3.2 Static and Dynamic Scopes
    7.4 TSDL Examples
+8. Clocks
 
 
 1. Preliminary definitions
@@ -1244,6 +1245,78 @@ struct {
 }
 
 
+8. Clocks
+
+Clock metadata allows to describe the clock topology of the system, as
+well as to detail each clock parameter. In absence of clock description,
+it is assumed that all fields named "timestamp" use the same clock
+source, which increments once per nanosecond.
+
+Describing a clock and how it is used by streams is threefold: first,
+the clock and clock topology should be described in a "clock"
+description block, e.g.:
+
+clock {
+	name = cycle_counter;
+	uuid = "62189bee-96dc-11e0-91a8-cfa3d89f3923";
+	description = "Local CPU cycle counter";
+	freq = 1000000000;	       /* frequency, in Hz */
+	/* precision in seconds is: 1000 * (1/freq) */
+	precision = 1000;
+	/* clock value offset from Epoch is: offset * (1/freq) */
+	offset = 1326476837897235420;
+};
+
+The mandatory "name" field specifies the name of the clock identifier,
+which can later be used as a reference. The optional field "uuid" is the
+unique identifier of the clock. It can be used to correlate different
+traces that use the same clock. An optional textual description string
+can be added with the "description" field. The "freq" field is the
+initial frequency of the clock, in Hz. If the "freq" field is not
+present, the frequency is assumed to be 1000000000 (providing clock
+increment of 1 ns). The optional "precision" field details the
+uncertainty on the clock measurements, in (1/freq) units. The "offset"
+field indicates the offset from POSIX.1 Epoch, 1970-01-01 00:00:00 +0000
+(UTC), to the zero of value of the clock, in (1/freq) units. If the
+"offset" field is not present, it is assigned the 0 value.
+
+Secondly, a reference to this clock should be added within an integer
+type:
+
+typealias integer {
+	size = 64; align = 1; signed = false;
+	map = clock.cycle_counter.value;
+} := uint64_ccnt_t;
+
+Thirdly, stream declarations can reference the clock they use as a
+time-stamp source:
+
+struct packet_context {
+	uint64_ccnt_t ccnt_begin;
+	uint64_ccnt_t ccnt_end;
+	/* ... */
+};
+
+stream {
+	/* ... */
+	event.header := struct {
+		uint64_ccnt_t timestamp;
+		/* ... */
+	}
+	packet.context := struct packet_context;
+};
+
+For a N-bit integer type referring to a clock, if the integer overflows
+compared to the N low order bits of the clock prior value, then it is
+assumed that one, and only one, overflow occurred. It is therefore
+important that events encoding time on a small number of bits happen
+frequently enough to detect when more than one N-bit overflow occurs.
+
+In a packet context, clock field names ending with "_begin" and "_end"
+have a special meaning: this refers to the time-stamps at, respectively,
+the beginning and the end of each packet.
+
+
 A. Helper macros
 
 The two following macros keep track of the size of a GNU/C structure without
@@ -1315,6 +1388,7 @@ keyword: is one of
 align
 const
 char
+clock
 double
 enum
 event