Filter
Top Products
6–6 Alpha Architecture Handbook
6.7.1 Drain Aborts
Format:
Operation:
IF PS<literal>(<)CM> NE 0 THEN
{privileged instruction exception}
{Stall instruction issuing until all prior
instructions are guaranteed to complete
without incurring aborts.}
Exceptions:
Instruction mnemonics:
Description:
If aborts are deliberately generated and handled (such as nonexistent memory aborts while siz-
ing memory or searching for I/O devices), the DRAINA instruction forces any outstanding
aborts to be taken before continuing.
Aborts are necessarily implementation dependent. DRAINA stalls instruction issue at least
until all previously issued instructions have completed and any associated aborts have been
signaled, as follows:
• For operate instructions, this usually means stalling until the result register has been
written.
• For branch instructions, this usually means stalling until the result register and PC have
been written.
• For load instructions, this usually means stalling until the result register has been writ-
ten.
• For store instructions, this usually means stalling until at least the first level in a poten-
tially multilevel memory hierarchy has been written.
For load instructions, DRAINA does not necessarily guarantee that the unaccessed portions of
a cache block have been transferred error free before continuing.
For store instructions, DRAINA does not necessarily guarantee that the ultimate target loca-
tion of the store has received error-free data before continuing. An implementation-specific
technique must be used to guarantee the ultimate completion of a write in implementations that
have multilevel memory hierarchies or store-and-forward bus adapters.
CALL_PAL DRAINA
!PALcode format
Privileged Instruction
CALL_PAL DRAINA Drain Aborts