LPC1778 EMAC Module: Clarification Required

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Tue Nov 25 09:58:18 MST 2014
On the 1778 (and presumably other devices with the EMAC block), there is a 'Maximum Frame Register' to set the maximum size for
received frames. [NOTE this is with the HUGE FRAMES option bit disabled.]

The power on default is 1536 bytes, conveniently larger than the maximum size of 1518/1522 for Ethernet frames/ VLAN tagged frames.

If the size is set to say 576 bytes, what actually happens when a over large frame appears on the wire?

Is it transparently ignored?

Is part of the frame stored?

Does the large frame use up a receive descriptor? Can the DMA ever write past the descriptor size (corrupting the following buffer?)

If so, what flags are set (if any) in the receive status word?

And which (if any) interrupt status flags are set.

The UM is completely silent on this issue.


Further more, if I attempt to transmit from a buffer exceeding the Ethernet maximum frame size,
what happens?

Is the transmission automatically fragmented? Even if the 'Do Not Fragment' bit is set?
If not, what error and or interrupt status flags are raised.

Regards, Mike

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Thu Jan 29 03:32:26 MST 2015
Thank you for this observation.

[lpcware]

Content originally posted in LPCWare by TheFallGuy on Wed Jan 28 11:17:09 MST 2015
I think you are going to need to ask NXP tech support through their Get Support menu on the main NXP website.

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Wed Jan 28 10:54:18 MST 2015
BUMP!!

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Tue Dec 30 12:41:52 MST 2014
Come on NXP. Over two months and still no reply.

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Thu Dec 04 19:17:51 MST 2014
This question has been pending for 10 days now.

I am given to understand that NXP monitor the MCU forums (It says so in the forum list).
Is it just pot luck if a (serious) question gets answered; do they go on to a todo list, etc.

Or are 'hard' questions skipped?

Note: I am not demanding that someone do my homework for me.
I am not saying give me the answer because I can not be bothered to search posts myself.

A search (and a Google site specific search) did not get any useful hits.

The information is simply not in the user manual.

Regards, Mike