How to record data logs in full resolution for unlimited period of time?

[mliberty]

Hi @jst and welcome to the forum! This forum is the perfect place for these questions.

@jst

a) I saw the examples of downsampled logging but I cannot figure out how do I log data for the longer period of time without downsampling at full resolution and the recording to only stop when CTRL+C is pressed. Am I missing something obvious here?

Capturing data to a JLS file is not hard, but it’s not trivial either. I just added a capture_jls.py example that records at full rate until you press CTRL-C.

@jst

b) Maybe this question is not even joulescope related, but why do we need to define the buffer in stream_by_callback example and what exactly does the stream_notify does there?

In read_by_callback.py, the StreamProcess.stream_notify method gets called when new data is available. The “self._buffer” is part of the implementation to store up to the first length samples. Your code will do whatever you want, but likely will call stream_buffer.samples_get to get the most recent data.

@jst

c) In downsample logging the frequencies are 1, 2, 4, 10, 20, 50, 100 . Where do these values come from? What prevents me from defining arbitrary value for frequency like 6 or 25?

The reduction frequencies are enumerated as a parameter. These values allow for simple and convenient UI selection. You could hack the code to define you own reductions here. In downsample_logging.py, you could specify a frequency of 100 with the command-line option:

--downsample 4

to give 25 Hz. 6 Hz requires a factor of 3, which does not divide evenly into any of the predefined downsampling frequencies. Does this simplified selection matter for your application?

@jst

d) and what value does the use of weakref adds in downsample_logger.

In general, weakrefs allow a way to break cycles of circular references so that the Python garbage collector can do its job. In this case, it prevents a circular reference from LoggerDevice back to its parent, Logger, which also maintains a reference to LoggerDevice. Since the entire program exits together, removing the weakref would likely not affect behavior. However, it’s good practice to maintain clean child-parent relationships where the part holds the child reference, but not the other way around.