How does one use the IDX field in an advanced transmit data descriptor?
I'm trying to understand this statement from
http://www.intel.com/content/www/us/en/ethernet-controllers/82599-10-gbe-controller-datasheet.html
:
>From page 344 regarding transmit contexts:
"The 82599 supports two contexts for each of its 128 transmit queues. The
IDX
bit contains an index to one of these two contexts. Each advanced data
descriptor that uses
any of the advanced offloading features must refer to a context by
the IDX field."
Where are these two contexts? How do I access them? It seems, in the
ixgbe driver for linux, that the idx field in the advanced transmit data
descriptor is never set ( is left at zero ) but rather an advanced transmit
context descriptor is put in the tx ring buffer before an advanced transmit
data descriptor. For example, if you want to do offloading, you:
1. fill in an advanced transmit context descriptor and put it on the
tx_ring ( ixgbe_tx_ctxtdesc
<http://lxr.free-electrons.com/ident?i=ixgbe_tx_ctxtdesc> )
2. fill in a transmit data descriptor and put it on the tx_ring
Why doesn't it:
1. fill in one of these two contexts that are available on each 128
transmit queues and set it up for offloading.
2. fill in the idx field of the advanced transmit data so that idx selects
the context that was filled out in step (1).
Which is what the documentation seems to imply. Does the documentation
even say that an advanced transmit context descriptor applies to the next
packet sent if idx is left at zero?
Thanks,
Doug
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