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LATEST_CHANGES.txt
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LATEST_CHANGES.txt
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Version 20200412.1 has the following significant changes, as well as
cosmetic and bug fixes:
1. Output resolution is now 11 decimal places rather than 12. The last
(1 ps) digit of the TICC output is purely noise and adds no information.
It also contributes to issues with floating point precision (see below).
The number of decimal places to print is set in the PLACES define in
config.h.
2. The configuration menu has been restructured because I ran out of
useful mnemonics. The commands are now simply identified by sequential
letters.
3. It is possible to configure a timestamp "rollover" or "wraparound"
value via the "G" command in the config menu. The default is 0 which means
there is no rollover and timestamps will increase indefinitely for the
next few million years. Setting the value to 1 means the wrap will happen
at 10 (one "0"), to 2 means 100 (two "0"s), etc. Using rollover is a way
to avoid loss of floating point precision (see below).
4. The config menu item "Master/Slave" has been changed to "Host/Client".
The functionality is the same.
5. The new "I" command, "channel name" allows you to assign names other than
the default "A" and "B" to the two channels.
ON FLOATING POINT PRECISION
Most computer programs process non-integer numeric data using floating point
operations that have about 15.9 digits of precision. If the number's
combined integer and fractional places are 16 or more, the accuracy of the
last decimal places is reduced. This effect becomes apparent on long
timestamp series of low-noise data; if 12 decimal places are used to
represent single picoseconds, there is potential accuracy loss (which shows
up as noise) when the integer part of the timestamp exceeds 999 seconds,
though it is usually not apparent until 10000 seconds or greater. The
effect increases as the total number of digits increases.
This new firmware version has two features to remediate this problem:
First, the fractional part of the output is now 11 places (10 ps
resolution) instead of 12. Second, the integer part of the timestamp can
be set to wrap, like a car odometer, at 10/100/1000, etc. seconds. That
constrains the number of digits. Most time analysis software can
be set to compensate for the wraps.