Expose AxiLookBits in axi_burst_splitter to avoid logic explosion

[briann-bui]

Fixes #341.

This PR exposes the AxiLookBits parameter in axi_burst_splitter (and cascades it through to axi_burst_splitter_gran and axi_to_axi_lite).

Previously, the internal demux always instantiated with AxiLookBits hardcoded to the full IdWidth, which caused a massive logic explosion (counter array size of 2**IdWidth) when dealing with large AXI IDs. By exposing this parameter (defaulting to IdWidth for backwards compatibility), users can now override it appropriately.

[imchenwu]

Hi, thnaks for working on it :).

1. axi_burst_unwrap instantiates its internal demux with the same hardcoded .AxiLookBits(IdWidth) and should also expose this parameter, otherwise it has the same issue.
2. When exposing the new parameter, please add a one-line comment explaining its usage and the implicit constraint (AxiLookBits <= AxiIdWidth). You can simply point to the existing documentation in doc/axi_demux.md.
3. It would be good to add a parameter check in the end of axi_burst_splitter_gran, e.g.

    assume (AxiLookBits > 0 && AxiLookBits <= IdWidth) else
      $fatal(1, "AxiLookBits (%0d) must be in ]0, IdWidth (%0d)]!", AxiLookBits, IdWidth);

also add the corresponding check in axi_to_axi_lite module.

[briann-bui]

Hi @imchenwu, I've pushed a new commit to address all 3 of your requested changes. Could you please take another look when you have a moment? Thanks!

[briann-bui]

@imchenwu, I have addressed all six review threads in commit 4089aac5:

• added the requested AxiLookBits/AXI_LOOK_BITS parameter documentation;
• moved the AxiLookBits parameter check from axi_burst_splitter_gran_counters into axi_burst_splitter_gran;
• verified the complete synthesis source set and axi_synth_bench compile successfully with Bender 0.30.0 and VCS X-2025.06.

All conversations are resolved. Could you please review again when convenient? Thanks!

[briann-bui]

Hi @imchenwu, thanks for approving this PR. Is there anything else needed before it can be merged?

[imchenwu]

Hi @briann-bui this PR changes the ports and downstream calling modules will require an update, so I would merge it in the next major release, together with the official release of common_cells v2.