BSP Developer's Guide

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Implementing a MUX-Based Network Interface Driver
To establish a memory pool, call netPoolInit( ). For an END, make the
netPoolInit( ) call during the driver’s initialization phase. From out of this pool,
your driver should reserve the mBlk/clBlk/cluster constructs it needs to receive
a packet. For more information, see the reference entry for netBufLib.
Receiving Data into Clusters
During the initialization phase of your END, call netClusterGet( ) to reserve some
reasonable number of clusters to receive incoming packets (store references to
these reserved clusters in a buffer ring or some other structure appropriate to your
needs). When a packet arrives, your END should receive it directly into one of
these clusters.
When your END is ready to pass a received packet up to the MUX, it does so using
an mBlk/clBlk/cluster construct. To create this construct:
1. Call netClBlkGet( ) to reserve a clBlk structure.
2. Call netClBlkJoin( ) to join the clBlk to the cluster containing the packet.
3. Call netMblkGet( ) to reserve a mBlk structure.
4. Call netMblkClJoin( ) to join the mBlk structure to the clBlk/cluster
construct.
Now that the packet is contained within an mBlk/clBlk/cluster construct, the
END can use various netBufLib routines to adjust or inspect the data in the
mBlk/clBlk/cluster construct. For example, to read the packet data in the
construct, your END can call netMblkToBufCopy( ). In addition, your END can
use the mBlk chaining feature to prepend or append data to the packet.
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NOTE: The various net*Get( ) routines reserve memory from a pre-allocated pool.
Internally, they do not use semaphores. Thus, they are safe to call from places
where a call to malloc( ) would be impossible.
Freeing mBlks, clBlks, and Clusters
When you are done with an mBlk/clBlk/cluster chain and want to return it to the
memory pool, call netMblkClChainFree( ). This frees all mBlks in the chain. It
also decrements the reference counters in all the clBlks in the chain. If the reference
counter for a clBlk drops to zero, that clBlk and its associated cluster are also freed
back to the pool. To free a single mBlk/clBlk/cluster back to the memory pool, use
netMblkClFree( ). For more information on these and other free routines, see the
reference entry for netBufLib.
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