Hello to everyone, I have a question for the developers of the Caravel chip, in details its fixed part, I mean MGMT part and RV core. What was the principal factor to use Wishbone bus, simplicity, hardware footprint ? Had You had considered the AXI protocol during the design?

Doesn't AXI require that without ARM's license you cant execute a single ARM instruction? I think its going to be a limiting factor number one.

@User as far as I know AXI is a part of AMBA which is an open, royalty free standard

Well, the real answer to that is that we started with the PicoRV32, and the PicoRV32 has an implementation using Wishbone that is part of the repository, so that was the fastest route to a bus-oriented solution.

@User Thank You for response and what do You think about making effort to implement SoC with the AMBA bus with AXI interfaces ?

"1. Subject to the provisions of Clauses 2, 3 and 4, ARM hereby grants to LICENSEE a perpetual, non-exclusive, non-transferable, royalty free, worldwide licence to: (i) use and copy the relevant AMBA Specification for the purpose of developing and having developed products that comply with the relevant AMBA Specification; (ii) manufacture and have manufactured products which either: (a) have been created by or for LICENSEE under the licence granted in Clause 1(i); or (b) incorporate a product(s) which has been created by a third party(s) under a licence granted by ARM in Clause 1(i) of such third party's ARM AMBA Specification Licence; and (iii) offer to sell, sell, supply or otherwise distribute products which have either been (a) created by or for LICENSEE under the licence granted in Clause 1(i); or (b) manufactured by or for LICENSEE under the licence granted in Clause 1(ii). 2. LICENSEE hereby agrees that the licence granted in Clause 1 is subject to the following restrictions: (i) where a product created under Clause 1(i) is an integrated circuit which includes a CPU then either: (a) such CPU shall only be manufactured under licence from ARM; or (b) such CPU is neither substantially compliant with nor marketed as being compliant with the ARM instruction sets licensed by ARM from time to time;" First page when you press on AXI4 specification. Looks like I missunderstood the clause 2b which says that it cant be " substantially compliant ". Still too restrictive to be called "Open source". This was dealbreaker for me. What if somebody runs an ARM emulator on my CPU does that count as being " substantially compliant ".