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diff --git a/doc/TIMESTAMPS.rst b/doc/TIMESTAMPS.rst new file mode 100644 index 0000000..458f462 --- /dev/null +++ b/doc/TIMESTAMPS.rst @@ -0,0 +1,30 @@ +Some knowledge accumulated about timestamping +============================================= + +The meaning of the timestamps changed between v2.3.1 and v3.0.0, this document gives some guidance about the interaction between different settings. + +The following table tries to summarise the differences. + ++-----------------------------+----------------------------------------------+-------------------------------------+-----------------------------------------------+ +| ODR-DabMux version | Meaning of timestamp inside EDI | ODR-ZMQ2EDI wait time w | Offset that should be set in the mod | ++=============================+==============================================+=====================================+===============================================+ +| Up to and including v2.3.1 | t_frame = t_mux (No offset in mux available) | positive, meaning delay after t_mux | Something larger than w + mod processing time | +| Later than v2.3.1 | t_frame = t_tx = t_mux + tist_offset | negative, meaning delay before t_tx | Something larger than mod processing time | ++-----------------------------+----------------------------------------------+-------------------------------------+-----------------------------------------------+ + +For historical reasons, ODR-DabMod decodes absolute timestamp from MNSC, not from “EDI seconds”. +The edilib tool decodes both EDI timestamp and MNSC, and can be used to verify both are identical. + +Issues in ODR-DabMux v2.3.1 +--------------------------- + +Running ODR-DabMux against the absolute timestamp firmware has uncovered a few issues: + + * At startup, the UTCO was not properly applied to the EDI seconds. This offset was 5 seconds (TAI-UTC offset - 32s, see EDI spec); + * odr-zmq2edi did not compensate for UTCO, hiding the above issue; + * ODR-DabMux needs a configurable offset; + * (minor) MNSC and EDI timestamps did not use the same internal representation, making it difficult to prove that they encode the same value; + * (minor) odr-zmq2edi swapped endianness when regenerating EDI from ETI (minor because only ODR-DabMod considers MNSC, and usually isn't used with EDI); + +**Important** Do not combine odr-zmq2edi with odr-dabmux of a different version! + |