Daniel Kruger

MCF5484 FEC and fast responses

Discussion created by Daniel Kruger on Jul 13, 2006
Latest reply on Jul 17, 2006 by Michael Norman

we want to develop a FEC driver for the MCF5484 that is able to respond to a special ethernet frame with a latency as low as possible.

We found two possibilities to reduce the latency.
1. Set the GTS flag in the FEC_TCR register to disable transmission of frames. Copy frame to transmit FIFO. Reset GTS flag when special frame was received.

2. Enable FEC interrupt for BABR events and set MAX_FL to 0. This mimic an early receive interrupt (why is there no receive interrupt for the FEC in MCF5484?). But this interrupt is also triggered after the frame was fully received from the bus. It is possible to check the first bytes of the frame and reset the GTS flag if necessary.

Are there any other possibilites to further reduce the receive-transmit-latency? Is there any interrupt source which signals right after the first 16 bytes of the frame are received?

Thank you for your help in advance.