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doc: clarify usage of HARQ in bbdev

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New paragraph is added for detailing typical VRAN usecase
and mapping to bbdev API usage.

Signed-off-by: Nicolas Chautru <nicolas.chautru@intel.com>
Reviewed-by: Tom Rix <trix@redhat.com>
This commit is contained in:
Nicolas Chautru 2021-09-07 18:15:40 -07:00 committed by Akhil Goyal
parent 765f42f1bd
commit d7e3805608
1 changed files with 31 additions and 0 deletions
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doc/guides/prog_guide/bbdev.rst
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@ -1054,6 +1054,37 @@ capability RTE_BBDEV_LDPC_INTERNAL_HARQ_MEMORY_OUT_ENABLE is set
then the HARQ is stored in memory internal to the device and not visible
to BBDEV.
.. note::
More explicitly for a typical usage of HARQ retransmission
in a VRAN application using a HW PMD, there will be 2 cases.
For 1st transmission, only the HARQ output is enabled:
- the harq_combined_output.offset is provided to a given address.
ie. typically an integer index * 32K,
where the index is tracked by the application based on code block index
for a given UE and HARQ process.
- the related operation flag would notably include
RTE_BBDEV_LDPC_HQ_COMBINE_OUT_ENABLE and RTE_BBDEV_LDPC_HARQ_6BIT_COMPRESSION.
- note that no explicit flush or reset of the memory is required.
For 2nd transmission, an input is also required to benefit from HARQ combination gain:
- the changes mentioned above are the same (note that rvIndex may be adjusted).
- the operation flag would additionally include the LDPC_HQ_COMBINE_IN_ENABLE flag.
- the harq_combined_input.offset must be set to the address of the related code block
(ie. same as the harq_combine_output index above for the same code block, HARQ process, UE).
- the harq_combined_input.length must be set to the length
which was provided back in the related harq_combined_output.length
when it has processed and dequeued (previous HARQ iteration).
The output mbuf data structures are expected to be allocated by the
application with enough room for the output data.