Write Back Queue WritebackQueue
Functional Description
The Writeback Queue contains 18 WritebackEntry items, responsible for writing back replacement blocks to the L2 Cache through the C channel of TL-C (Release) and responding to Probe requests (ProbeAck).
Feature 1: WritebackQueue Entry Allocation and Rejection
For timing considerations, new requests will be rejected when the wbq is full; when the wbq is not full, all requests will be accepted, and an empty entry will be allocated for the new request. The current version no longer supports merging requests in the WritebackQueue.
Feature 2: Request Blocking Conditions
The TileLink specification imposes restrictions on concurrent transactions, requiring that if a master has a pending Grant (i.e., GrantAck has not yet been sent), it cannot issue a Release for the same address. Consequently, any miss request entering the MissQueue that detects an entry with the same address in the WritebackQueue will be blocked.
Overall Block Diagram
The overall architecture of the WritebackQueue is shown in 此图.
Interface timing
Request Interface Timing Example
此图 shows the interface timing of a request that needs to be written back to L2 in the WritebackQueue.
WritebackEntry Module
WritebackEntry State Machine Design
State Design: The state machine design in WritebackEntry is shown in 此表 and 此图:
| Status | Descrption |
|---|---|
| s_invalid | Reset state, this WritebackEntry is an empty entry |
| s_release_req | Sending a Release or ProbeAck request |
| s_release_resp | Waiting for ReleaseAck Request |
