manual: expand the protocol decoder troubleshooting subsection

[pulseview.git] / manual / decoders.txt

diff --git a/manual/decoders.txt b/manual/decoders.txt
index aef3034b2f88cccf65b286ececde727b34258de9..27e79b4e53f5de41ca8000d4a8117e0a001d2f6a 100644 (file)
--- a/manual/decoders.txt
+++ b/manual/decoders.txt
@@ -78,6 +78,39 @@ as you can now visually understand where the ranges for high and low are placed.
 Aside from the default conversion threshold(s), you can choose from a few common presets
 or enter custom values as well. They take the form "0.0V" and "0.0V/0.0V", respectively.
 
+=== Troubleshooting
+
+In case a protocol decoder doesn't provide the expected result, there are several things
+you can check.
+
+The first check you should perform is whether the time unit in the ruler
+is given as "sa". This is short for "samples" and means that the device didn't provide
+a sample rate and so PulseView has no way of showing a time scale in seconds or
+fractions thereof. While some decoders can run without timing information, or only
+optionally make use of the time scale, others may not be able to interpret the
+input data since timing information is an essential part of the very protocol.
+
+Another issue to remain aware of is that decoders need enough samples per protocol step
+to reliably interpret the information. In typical cases the minimum sample rate should
+be four to five times the rate of the fastest activity in the protocol.
+
+If a protocol decoder runs but shows you annotations that don't seem to make any sense,
+it's worth double-checking the decoder settings. One common source of error is the
+baud rate. For example, the CAN protocol decoder doesn't know what baud rate
+is used on the bus that you captured, so it could be that a different baud rate is used
+than the one you set. Also, if this is still not the reason for the malfunction, it's
+worth checking whether any of the signals have been captured inverted. Again using the
+CAN bus as an example, the decoder will decode the signal just fine if it's inverted but
+it'll show data even when the signal looks "idle".
+
+When a protocol decoder stops execution because of an unmet constraint (required input
+not connected, essential parameter not specified) or a bug in the decoder itself, you
+will be presented a static red message in the protocol decoder's display area.
+In that case, you check the log output in the settings menu. There you'll find the Python
+error description which you can use to either adjust the configuration,
+or debug the decoder (and let us know of the
+fix) or you can copy that information and file a bug report so that we can fix it.
+
 === Exporting Annotations
 
 If you want to postprocess annotations that were generated by a protocol decoder, you