This plugin for Saleae Logic allows you to analyze a CPPM stream as commonly found in RC receivers.
Defaults should generally work, but there are a few parameters that may occasionally come in handy:
This is the minimum amount of time signal will be held high (or low) to be considered a frame boundary by the analyzer. 2500μS is good for most streams.
The sync signal may be high (normal) or low (inverted). "Auto" doesn't care whether it's high or low and just looks for anything matching the min sync time.
The number of channels within a frame is automatically determined in most cases, however, there was a known bug in the FrSky D4R that led to channel values being truncated and frames being smashed together making it impossible to infer a boundary.
If you know your stream will only contain 8 channels, but are finding things hinting at this bug, you can set the maximum channel count to 8 and instead of the severely limited pulse being considered channel 9, it'll be marked as an error like this:
These errors are also flagged on export streams. In wide form, the row will be marked as an error when the channel count got reset because of error. In the long form, the actual erroring value will appear on its own with its timestamp and width.
Minimum change is a sort of deadband across any changes that prevents you from seeing too much noise. If you set it to 0, there will be a marker, label, and search result for each change.
The default of 3 means that a particular channel has to move at least 3μS before the value is considered significant. Smaller changes will still get a bubble label at the top, but they won't have a distinct search result, nor will they get a change marker.
There are two export formats.
One is a wide format csv that is timestamped with the beginning of a cppm frame and includes a column for every channel found in the frame. e.g.:
Time [s],ch1,ch2,ch3,ch4,ch5,ch6,ch7,ch8,error
0.020300000000000,984,1502,1499,1504,1502,1501,1502,1932,
0.040300250000000,984,1502,1498,1504,1501,1502,1502,1932,
0.060300250000000,984,1502,1499,1504,1502,1501,1502,1932,
0.080300375000000,984,1503,1496,1505,1502,1501,1502,1932,
0.100300375000000,984,1503,1496,1504,1501,1502,1501,1932,
0.120300625000000,984,1504,1497,1504,1501,1502,1501,1940,
0.140300750000000,984,1505,1499,1504,1502,1501,1502,1940,
0.160300875000000,984,1502,1499,1505,1502,1502,1501,1940,
0.180300875000000,984,1502,1498,1505,1502,1501,1502,1940,
The second is a long form csv with a row for every channel picked up at the timestamp where it was found. e.g.:
Time [s],val,chan,error
0.000299875000000,984,1,
0.001284125000000,1502,2,
0.002786375000000,1499,3,
0.004285500000000,1504,4,
0.005789750000000,1502,5,
0.007291875000000,1501,6,
0.008793125000000,1502,7,
0.010295250000000,1932,8,
0.020300000000000,984,1,
In addition to giving you more exact timestamps per channel, this form is handy for building long-format data frames in r for doing stuff like this in ggplot:
Download the Logic SDK and extract it somewhere on your
machine. In my case, it's ~/stuff/SaleaeAnalyzerSdk-1.1.32.
Clone the repo and cd into the top level of it:
git clone https://github.com/dustin/logic-cppm
cd logic-cppm
Symlink the include and lib directories into your tree:
ln -s ~/stuff/SaleaeAnalyzerSdk-1.1.32/{include,lib} .
Run the build script:
./build_analyzer.py
In the Develoepr tab in Logic preferences, specify the path for loading new plugins, then copy the built plugin into that location:
cp release/* /path/specified/in/Logic/preferences