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20.3.1 CALL_PAL Instruction

 

CALL_PAL is the only architecturally valid entry point into PAL mode (aside from exception/interrupt vectors). It encodes a PAL function selector in bits [25:0], does not behave like a normal subroutine call, and implies full serialization (MemoryBarrierKind::PAL = 0xFFFF). Before PAL code begins: all prior instructions must complete, write buffers must be drained, LL/SC reservations must be cleared, speculative instructions must be discarded, interrupts must be masked (IPL raised to 7), and the pipeline must be flushed.

 

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20.3.2 Vector Calculation

 

PAL entry vectors are computed differently for exceptions/interrupts (direct vectors from PalVectorTable) and CALL_PAL instructions (calculated offsets from PAL_BASE):

 

 

This produces 128 possible entry points spaced 64 bytes apart (enough for a short PAL dispatch stub per function). The computeCallPalEntry() method performs this calculation. Examples: CALL_PAL HALT (0x00) → PAL_BASE + 0x2000, CALL_PAL CSERVE (0x09) → PAL_BASE + 0x2240, CALL_PAL CALLSYS (0x83) → PAL_BASE + 0x30C0.

 

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20.3.3 EV6 Exception Vectors

 

Exception and interrupt vectors are fixed offsets from PAL_BASE, defined by PalVectorId_EV6 (Alpha 21264 Hardware Reference Manual, Table 5-8):

 

 

For exceptions and interrupts, the entry PC is PAL_BASE + vectorOffset, passed directly to enterPal().

 

See Also: palLib_EV6/PalVectorId_refined.h; palLib_EV6/PalVectorTable_final.h; 8.5 PAL Vector Dispatch; Alpha 21264 Hardware Reference Manual, Table 5-8.