marchid

Machine Architecture ID

The marchid CSR is an MXLEN-bit read-only register encoding the base microarchitecture of the hart. This register must be readable in any implementation, but a value of 0 can be returned to indicate the field is not implemented. The combination of mvendorid and marchid should uniquely identify the type of hart microarchitecture that is implemented.

Open-source project architecture IDs are allocated globally by RISC-V International, and have non-zero architecture IDs with a zero most-significant-bit (MSB). Commercial architecture IDs are allocated by each commercial vendor independently, but must have the MSB set and cannot contain zero in the remaining MXLEN-1 bits.

The intent is for the architecture ID to represent the microarchitecture associated with the repo around which development occurs rather than a particular organization. Commercial fabrications of open-source designs should (and might be required by the license to) retain the original architecture ID. This will aid in reducing fragmentation and tool support costs, as well as provide attribution. Open-source architecture IDs are administered by RISC-V International and should only be allocated to released, functioning open-source projects. Commercial architecture IDs can be managed independently by any registered vendor but are required to have IDs disjoint from the open-source architecture IDs (MSB set) to prevent collisions if a vendor wishes to use both closed-source and open-source microarchitectures.

The convention adopted within the following Implementation field can be used to segregate branches of the same architecture design, including by organization. The misa register also helps distinguish different variants of a design.

Attributes

Defining Extension

  • Sm, version >= 0

CSR Address

0xf12

Length

32-bit

64-bit

Privilege Mode

M

Format

This CSR format changes dynamically.

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Field Summary

Name Location Type Reset Value

Architecture

63:0

RO

ARCH_ID

Fields

Architecture

Location

63:0

Description

Vendor-specific microarchitecture ID.

Type

RO

Reset value

ARCH_ID