[etherlab-dev] Support for inplace Input/Output PDO exchange (LRW cmd: Input data overwrites output data)

martin troxler martin.troxler at komaxgroup.com
Wed Apr 28 14:59:22 CEST 2010


are there any plans to fully support the mapping of input data to the
same logical address as the outputs? The ESC Asic supports this through
the LRW command and is already used by TwinCAT!

This would reduce the size of the sent/received ECAT frame almost by
half: We have a refresh rate of 4kHz and control over 20 Servo devices
with FSoE, so there is not much "space" to send multiple frames within

I researched the code a bit and realized that the FMMU setup could be
changed so that successive FMMUs with opposite direction could use the
same logical address as the previous configured FMMU.
A more tricky problem is that the domain datagrams point directly to the
domain data and that data is just memcpy-ed to/from the frame. Perhaps
the domain FMMUs may be used to access just parts of the domain data.


Martin Troxler
Komax AG

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Thank You.

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