scatter gather DMA in OPB MAC core

[prav]

Hi all,

I wanted to know how scatter gather DMA is different from normal DMA
operations.scatter gather DMA concept is used in OPB ethernet core.
I am not getting any good resources on this .Suggesting any good links
on scatter gather DMA would be appreciated.

rgds,
prav

 

[Stan Lackey]

"Normal" DMA architectures define packet buffers with addresses that
increment, that is, the set of buffers might occupy memory addresses
10000-1FFFF for a 64K-byte queue. This has the advantage that it's easy to
implement, however it is inflexible, since each queue has a fixed size you
set up at boot time (probably at design time, actually.) If you only have a
few queues, or lots of memory, this is probably OK.

With "scatter-gather" architecture, on the other hand, each buffer might
have a link to another buffer, or there might be an array (map) of addresses
of buffers. You don't get from one buffer to the next by incrementing the
address, you get there by following a pointer. This plan is better if you
need lots of queues and they all don't have to be max size simultaneously.
Scatter-gather lets you dynamically allocate memory to a queue on-demand,
and make better use of memory.

-Stan

"prav" <praveenkn123@yahoo.com> wrote in message
news:863df22b.0406182045.5fd5693b@posting.google.com...

Hi all,

I wanted to know how scatter gather DMA is different from normal DMA
operations.scatter gather DMA concept is used in OPB ethernet core.
I am not getting any good resources on this .Suggesting any good links
on scatter gather DMA would be appreciated.

rgds,
prav