Intel® Quartus® Prime Pro Edition User Guide: Platform Designer

ID 683609
Date 10/04/2021
Public

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5.1.11. Read and Write Responses

Platform Designer merges write responses if a write is converted (burst adapted) into multiple bursts. Platform Designer requires read response merging for a downsized (wide-to-narrow width adapted) read.

Platform Designer merges responses based on the following precedence rule:
DECERR > SLVERR > OKAY > EXOKAY

Adaptation between a host with write responses and an agent without write responses can be costly, especially if there are multiple agents, or if the agent supports bursts. To minimize the cost of logic between agents, consider placing the agents that do not have write responses behind a bridge so that the write response adaptation logic cost is only incurred once, at the bridge’s agent interface.

The following table describes what happens when there is a mismatch in response support between the host and agent.

Table 47.  Response Support for Mismatched Host and Agent
  Agent with Response Agent Without Response
Host with Response

Interconnect delivers response from the agent to the host.

Response merging or duplication may be necessary for bus sizing.

Interconnect delivers an OKAY response to the host
Host without Response Host ignores responses from the agent No need for responses. Host, agent and interconnect operate without response support.
Note:

If there is a bridge between the host and the endpoint agent, and the responses must come from the endpoint agent, ensure that the bridge passes the appropriate response signals through from the endpoint agent to the host.

If the bridge does not support responses, then the responses are generated by the interconnect at the agent interface of the bridge, and responses from the endpoint agent are ignored.

For the response case where the transaction violates security settings or uses an illegal address, the interconnect routes the transactions to the default agent. For information about Platform Designer system security, refer to Manage System Security. For information about specifying a default agent, refer to Error Response Agent in Platform Designer System Design Components.

Note: Avalon® memory mapped agents without a response signal are not able to notify a connected host that a transaction has not completed successfully. As a result, Platform Designer interconnect generates an OKAY response on behalf of the Avalon® memory mapped agent.