Proposed solution:

Add something like the following to the "Required Pad" section of the
PIG:

Any non critical section induced latency (e.g., hardware induced timer
interrupt latency) must also be accounted in "required pad".  In this
context, the latency does not include software induced latency just
the time between when the interrupt was supposed to be signaled to the
processor and when it actually was.

For example, if the CPU is not in a critical section (interrupts are
not disabled or masked), if the timer is programmed for 100us, and the
timer interrupt is not delivered to the CPU until (100+N)us, then N
must be added to "required pad".

Change "required pad" computation to be "worst possible+N".

Possibly add a note saying that we've seen modern pipelined
processors' interrupt response delayed by 10s of microseconds.

Note that non critical section induced latency is *not* measured by
the crittime kernel and thus not included in the ctxtime.py report.

Update PALSRD timerWRite() description to remind PAL developer to
convey to platform integrator the "non critical section induced
latency" so it can be included in "required pad".

In ctxtime.py:

Make help and the output reference the above.

Note that timer interrupt latency can cause "worst observed" to be
greater than "worst possible".  So can an improper timer
implementation.

Although the above is described as an enhancement, we are contacting
hardware to determine how much latency is possible, and how widespread
extended duration latency might be and whether an announcement to the
user community is appropriate.

The interrupt latency issue should also be referred to in the discussion on system tick jitter.

Excerpt of an e-mail from Doug Farrell on this topic:

FYI 

We recommend ctxtime and PIG be modifed to use equivalent terms.  We will need a companion PCR for ctxtime changes.

Recommend Deferral
The documentation is correct as written but could be made clearer, hence
Severity "Enhancement".

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