lowRISC / lowRISC/opentitan

[prim] Packer empty signal

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Component:RTL Earlgrey-PROD Triaged IP:hmac IP:prim Priority:P2 Type:Cleanup Type:FutureRelease
Dominant language
SystemVerilog
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Description

prim_packer does not have indicators out for the empty status. If partial bits are stored in the `prim_packer`, it cannot be known from outside.

This results in HMAC to rely on packer `rvalid` signal rather than empty signal.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by inspecting the prim_packer interface and its connection to HMAC, focusing on how partial bits are represented and how rvalid is used. Define the missing externally visible empty-status indication and verify that HMAC can distinguish an empty packer from one holding partial bits.

Written by the indexing model from the issue text.

Assessment

Domain
embedded-iot, security
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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