[Libre-soc-bugs] [Bug 713] PartitionedSignal enhancement to add partition-context-aware lengths

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Mon Oct 4 16:09:08 BST 2021


https://bugs.libre-soc.org/show_bug.cgi?id=713

--- Comment #4 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
insight:

initially thought, "why have gaps at all", why not have the alternative
length parts back-to-back.

Spec:

* 32bit -> 11 bit
* 16bit -> 2x 10 bit
* 8bit  -> 4x 8 bit

Actual layout:

* 32 bit   10..0
* 16 bit   19..10 plus 9..0
* 8 bit    31..24 23..16 15..8 7..0

no.

it has to be:

* 32 bit                      10..0
* 16 bit          25..16       9..0
* 8 bit    31..24 23..16 15..8 7..0

because of alignment and when "interacting" as the input/output involving
other (regularly sized) partitioned signals.

without the alignment to regular boundaries you actually need special
conditional partition-aware routing

very awkward.

alignment cleans that up.

but, has to have "gaps" as a result.

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