[etherlab-users] waiting for received frames

[Martin Troxler]

Hi

I watched that discussion about the need for a API to wait (poll) for 
received frames. I still don't get it why that is nessessary.

Here is a clarification of how ethercat (process data transfer) works:
- Process Data should be regarded as idempotent states, which means it 
doesn't matter how many times you read it.
- it's a kind of huge shift register from the master through all slaves 
and back to the master where each slave (ESC-Chip) manipulates the 
stream of data on the fly.
- Slaves (i.e. the firmware on microcontrollers) cannot delay the 
transmission of the frame. If there is no new data the ESC simply 
transfers the actual content of its local memory.
- The frame transmission time is fixed for a given set of slaves and 
depends largely on the domain size and not on how fast the slave's 
microcontroller can update the data.

Regards
Martin

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