Add missing CV-X-IF register interface signals

[LuisDonatien]

Add missing register ACK signals to be fully compliant with the CV-X-IF v1.0 interface. CV-X-IF Register Doc..

• RTL changes:

  • Add x_register_valid_o and x_register_ready_i ports in:

    • cve2_riscv_compliance.sv
    • cve2_top.sv
    • cve2_core.sv
    • cve2_id_stage.sv

  • (cve2_id_stage.sv) Forward x_issue_valid_o to x_register_valid_o, since their behavior is equivalent when X_ISSUE_REGISTER_SPLIT=0

  • (cve2_id_stage.sv) Assign x_register_ready_i to the unused signal unused_x_register_ready. This assumes that when X_ISSUE_REGISTER_SPLIT=0, the coprocessor can process the issue and register transactions simultaneously x_register_ready_i = x_issue_ready_i.

  • (cve2_pkg.sv) Add fixed coprocessor configuration parameter X_ISSUE_REGISTER_SPLIT=0

• Doc changes:

  • (integration.rst) Update cve2 CV-X-IF interface

[MikeOpenHWGroup]

Hi @LuisDonatien, thanks for this PR. Do you have any VIP related to this update you could share? This changes adds considerable complexity and our testbench currently lacks any means to test it.

[LuisDonatien]

Hello @MikeOpenHWGroup, I used an IP derived from the CVA6 cvxif_example coprocessor example. The following repository cvxif_coproc_example provides a template with guidelines on how to instantiate the coprocessor and connect it to the CV32E20. It also includes an assembly code with the custom instructions and the expected results.

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[MikeOpenHWGroup]

Thanks @LuisDonatien. It LTGM. I've assigned this review to @davideschiavone (the Committer who originally added the X-IF to this core), and also to CoPilot - just to see what it says.