Mark Butcher

Sending short Ethernet frames using M5223X/M5225X

Discussion created by Mark Butcher on Jul 12, 2009
Latest reply on Jul 13, 2009 by Tom Thompson

Hi All

 

Does anyone know the best method of sending frames shorter than 60 bytes over Ethernet?

 

In the M52235 user's manual the following is quoted: "18.4.6: Short Frames are automatically padded by the transmit logic (if the TC bit in the transmit buffer descriptor for the end of frame buffer equals 1)"

 

The transmitter thus always pads to 60 byte minimum length when the CRC generator is active.

This suggests that by generating the Ethernet CRC-32 in SW rather than letting the chip do it it should be possible but this will result in a high CPU load if generally used.

 

It has been identified that some WiFi gateways are not working with the M522XX due to the fact that they demand 42 byte long ARPs and padding them causes them to be rejected (which doesn't seem logical but at the moment this is the state of findings).

 

Does any one know of a more efficient solution?

 

Regards

 

Mark

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