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Improved description.

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sidney 2024-12-31 18:32:11 +01:00
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@ -265,13 +265,13 @@ address range. Six values are currently defined:
<p>Values $00 to $03 provide access to the latched (frozen) value of their respective live
counters at the time of the last write to <tt>PERIPHERALS_COUNTER_LATCH</tt>.
<p>When <tt>PERIPHERALS_COUNTER_LATCH</tt> equals $80, the <tt>PERIPHERALS_COUNTER_VALUE</tt>
will be a 64-bit value corresponding to the number of nanoseconds elapsed since Midnight, Jan 1st,
1970 UTC, at the time of the last latch operation.
<p>When <tt>PERIPHERALS_COUNTER_SELECT</tt> equals $80, the <tt>PERIPHERALS_COUNTER_VALUE</tt>
will be a 64-bit value corresponding to the number of nanoseconds elapsed since the Unix epoch
(Midnight, Jan 1st, 1970 UTC), at the time of the last latch operation.
<p>When <tt>PERIPHERALS_COUNTER_LATCH</tt> equals $81, the high 32 bits of <tt>PERIPHERALS_COUNTER_VALUE</tt>
will be a 32-bit value corresponding to the number of seconds elapsed since Midnight,
Jan 1st, 1970 UTC, at the time of the last latch operation. The low 32 bits of
<p>When <tt>PERIPHERALS_COUNTER_SELECT</tt> equals $81, the high 32 bits of <tt>PERIPHERALS_COUNTER_VALUE</tt>
will be a 32-bit value corresponding to the number of seconds elapsed since the Unix epoch (Midnight, Jan 1st,
1970 UTC), at the time of the last latch operation. The low 32 bits of
<tt>PERIPHERALS_COUNTER_VALUE</tt> will hold the nanoseconds since the start of that second.
<p>The two different wallclock-time latch registers will always refer to precisely the same time instant.
@ -279,10 +279,10 @@ For some applications, the single 64-bit value measured in nanoseconds will be m
for other applications, the split 32/32 bits representation with separate second and nanosecond
values will be more convenient.
<p>Note that the definition above, with time elapsed measured since Midnight, Jan 1st, 1970 UTC, is
an approximation, as the implementation depends on the way POSIX definition time. Unfortunately,
POSIX does not account for leap seconds; it incorrectly assumes that all days are precisely 86400 seconds
long.
<p>Note that the time elapsed since the Unix epoch is an approximation, as the implementation depends on the
way POSIX defines time-since-the-epoch. Unfortunately, POSIX incorrectly assumes that all days are precisely
86400 seconds long, which is not true in case of leap seconds. The way this inconsistency is resolved is
system dependent.
<p>On reset, <tt>PERIPHERALS_COUNTER_SELECT</tt> is initialized to zero. If the <tt>PERIPHERALS_COUNTER_SELECT</tt>
register holds a value other than one of the six values described above, all <tt>PERIPHERALS_COUNTER_VALUE</tt>