Downsizing Data Width Function - Altera Cyclone V Device Handbook

4-18
Incrementing Bursts
Incrementing Bursts
The interconnect converts all input INCR bursts that complete within a single output data width to an
INCR1 burst of the minimum SIZE possible, and packs all INCR bursts into INCR bursts of the optimal
size possible for maximum data throughout.
Wrapping Bursts
All WRAP bursts are either passed through unconverted as WRAP bursts, or converted to one or two INCR
bursts of the output bus. The interconnect converts input WRAP bursts that have a total payload less than
the output data width to a single INCR burst.
Fixed Bursts
All FIXED bursts pass through unconverted.
Bypass Merge
If the programmable bit bypass_merge is enabled, the interconnect does not alter any transactions that
could pass through legally without alteration. Bypass merge is accessible through the GPV registers and is
only accessible to secure masters.

Downsizing Data Width Function

The downsizing function reduces the data width of a transaction to match the optimal data width at the
destination. Downsizing does not merge multiple-transaction data narrower than the destination bus if the
transactions are marked as noncacheable.
The downsizing function reduces the data width by the following ratios:
• 2:1
• 4:1
Incrementing Bursts
The interconnect converts INCR bursts that fall within the maximum payload size of the output data bus
to a single INCR burst. It converts INCR bursts that are greater than the maximum payload size of the output
data bus to multiple INCR bursts.
INCR bursts with a size that matches the output data width pass through unconverted.
The interconnect packs INCR bursts with a SIZE smaller than the output data width to match the output
width whenever possible, using the upsizing function.
Related Information
Upsizing Data Width Function
Wrapping Bursts
The interconnect always converts WRAP bursts to WRAP bursts of twice the length, up to the output data
width maximum size of WRAP16, and treats the WRAP burst as two INCR bursts that can each be converted
into one or more INCR bursts.
Altera Corporation
on page 4-17
cv_54004
2013.12.30
Interconnect
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