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Perhaps an easy one on ethernet MAC chips
- From: Chuck McManis <ecos at mcmanis dot com>
- To: ECOS Discussion Group <ecos-discuss at sources dot redhat dot com>
- Date: Wed, 15 Feb 2006 21:56:37 -0800
- Subject: [ECOS] Perhaps an easy one on ethernet MAC chips
So the read descriptors are defined with some flags, a length, a pointer to
the data buffer, and a pointer to the next descriptor.
When the descriptor goes from being NIC_OWNED to being HOST_OWNED (because
the NIC put some data in it) the len now contains the actual length of the
packet received.
Before it had a packet in there, what should length be set to?
I noticed that _BUF_SIZE is hard coded to 1544 bytes. That's a pretty
standard 1500 byte MTU with 44 bytes of framing wrapped around it. The
length field is capable of representing up to 2047 bytes, and there are
flags to say the buffer is only part of the story. (multiple buffers could
have parts of packets in them). So how does the MAC know how much buffer
space it has to work with?
--Chuck
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