Issue 5320: The properties of timing devices (uml-scheduling-ftf)
Source: The MathWorks (Mr. Alan Moore, alan.moore(at)mathworks.co.uk)
Nature: Uncategorized Issue
Severity: 
Summary: "• The properties of timing devices are listed, but some of them are not explained, and
no clue is given as to measure or represent them. This is the case for stability and skew.
In particular, the relationship between skew and offset should be explicit.
• Last paragraph but one, last sentence, definition of drift: the definition does not appear
very clear to me: what can be the relative frequency of a clock between two successive
ticks? Is not the drift simply measured by (the absolute value of) the difference of fre-quencies?
(Frequency taken with the usual definition, one over the period.)
• Last paragraph, last sentence: It says that a timer is always associated with a particular
clock; this is not explicit on the diagram of fig. 5-3; in fact, according to this diagram,
a timer is indirectly and implicitly associated with (at least) two clocks, one coming
through inheritance from TimingMechanism (the reference clock) and the other com-ing
through the association with TimeValue, which is itself associated with a refer-ence
clock; there is no constraint to express that these two clocks should be the same.
Should they?"

Resolution: see above
Revised Text: Add the following footnote to first para on page 5-5: "A more precise definition of each of these characteristics can be found in [32]"
Actions taken:
May 22, 2002: received issue
June 30, 2003: closed issue
Discussion: 
Resolution:
The first two sub-issues have been resolved by providing an explicit reference to the latest version of the Enhanced View of Time Specification (formal/02-05-07) which contains the appropriate definitions (repeating these complex definitions in the RT profile spec would require repeating a substantial portion of text already specified in the EVT spec). 
The last sub-issue is rejected. They do not have to be the same. The timer is a timing mechanism in its own right and can have its own reference clock.

End of Annotations:=====
This is issue # 5320    Moore, Alan" <alan.moore@artisansw.com



The properties of timing devices


"no clue is given as to measure or represent them. This is the case
for stability and skew.
In particular, the relationship between skew and offset should be
explicit.
very clear to me: what can be the relative frequency of a clock
between two successive
ticks? Is not the drift simply measured by (the absolute value of) the
difference of fre-quencies?
(Frequency taken with the usual definition, one over the period.)
ar
clock; this is not explicit on the diagram of fig. 5-3; in fact,
according to this diagram,
a timer is indirectly and implicitly associated with (at least) two
clocks, one coming
through inheritance from TimingMechanism (the reference clock) and the
other com-ing
through the association with TimeValue, which is itself associated
with a refer-ence
clock; there is no constraint to express that these two clocks should
be the same.
Should they