<< Click to Display Table of Contents >> Navigation:  ASA-EMulatR Reference Guide > Introduction > Architecture Overview > Chapter 15 – Memory System Implementation Details > 15.6 Write Buffer Implementation

15.6.1 Per-CPU Write Buffer State

 

The WriteBufferManager maintains a CPUWriteBufferState for each CPU, containing a fixed array of 8 WriteBufferEntry slots (MAX_ENTRIES = 8), an atomic pendingCount, atomic drainRequested and drainInProgress flags, a per-CPU QMutex, and a QWaitCondition for drain synchronization. The manager is constructed with the active CPU count and supports up to MAX_CPUS (compile-time constant).

 

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15.6.2 Draining Rules

 

Write buffers are drained (all buffered stores committed) when any of the following conditions are met:

 

•MB instruction executes (full memory barrier)

•WMB instruction executes (write memory barrier)

•EXCB or TRAPB requires serialization

•PAL entry or exit occurs

•Certain exceptions are delivered

•System shutdown (flushAllBuffers() drains all CPUs in order)

 

The CBox calls drainCPU(cpuId, commitCallback) with a callback that commits each WriteBufferEntry to GuestMemory. The drain dequeues entries in FIFO order via dequeueWrite(), ensuring stores become visible in program order.

 

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15.6.3 Source Files

 

 

See Also: memoryLib/global_writeBufferManager.h – Singleton accessor and lifecycle; 14.5 CBox – Cache / Control Box (write buffer responsibilities).