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Address Translator

Overview

Address Translator is a component that forwards memory read and write requests with the translated addres Assuming that the core is using virtual addresses and the L1 cache is using physical addresses, an address translator can be placed in between the core and the L1 cache to perform the translation. The purpose of the Address Translator component is to decouple the memory logic with address translation and to enable users to configure the address translation at any level.

Parameters

Ports

An Address Translator defines 3 ports: TopPort, BottomPort, and TranslationPort.

Protocol

Address translator receives mem.ReadReq and mem.WriteReq from the TopPort, it guarantees that a corresponding type of response return to the request source at some time in the future.

Address translator sends vm.TranslationReq to the Translation Service Provider (TSP) through the TranslationPort. The TSP should guarantee the address get translated and sent back from the TranslationPort in the future.

Address translator also send mem.ReadReq and mem.WriteReq to other memory or cache component throught the BottomPort. Address translator expects to receive the response to the read and write request form the BottomPort.

Timing

Address Translator follows a pipelined design described in the following diagram.

Address Translator Pipeline

  1. Read and write requests that arrive at the Address Translator from the TopPort are extraced by the Translate stage. The Translate stage generates a vm.TranslationReq to the TSP and sent through the TranslationPort. In case the same page is currently being translated, no new request will be generated.

  2. Forward stage extracts the translation response from the TranlsationPort. It clones the original read and write requests and replaces the address with the translated physical address and replaces the PID with 0 (for physical address). The Forward stage sends the cloned requests throught the bottom port to the memory unit that can fulfill the read and the writ request. In case there are multiple requests for the same page, the forwarder forwards one request per cycle.

  3. The Respond stage receives responses from the BottomPort and sends the responds to the original requester throught the TopPort.