<< Click to Display Table of Contents >> Navigation:  ASA-EMulatR Reference Guide > Introduction > Architecture Overview > Chapter 6 - Serialization and Stall Model > 6.11 CALL_PAL as a Serialization Point

6.11.1 PAL Transition Semantics

 

CALL_PAL transitions execution into privileged PAL mode. This transition must be serialized to prevent speculative execution across privilege boundaries, inconsistent IPR state, and unsafe MMIO access.

 

6.11.2 Required Behavior

 

CALL_PAL behaves as the strongest serialization point (MemoryBarrierKind::PAL = 0xFFFF). It requires:

•All prior instructions complete

•Pipeline is flushed or drained

•LL/SC reservations are cleared

•Write buffers are drained

•Interrupts are masked during the transition

 

6.11.3 SMP Coordination

 

In SMP configurations, CBox::issueMemoryBarrier() checks the active CPU count. If more than one CPU is active and the barrier kind is PAL, the MemoryBarrierCoordinator initiates a global barrier and waits for all CPUs to acknowledge before the PAL transition completes:

 

// CBox::issueMemoryBarrier()

drainWriteBuffers(); // Step 1: local drain

if (activeCpuCount > 1 && kind == MemoryBarrierKind::PAL) {

 m_barrierCoordinator->initiateGlobalMemoryBarrier(m_cpuId, activeCpuCount);

 m_barrierCoordinator->waitForBarrierAcknowledge(m_cpuId);

}

m_state = CBoxState::RUNNING;

 

See Also: 4.9 PalBox - Privileged Architecture Library Box; CBoxLib/CBoxBase.h (issueMemoryBarrier).