Hardware and software speculation mechanisms

Issue the instruction if there is an empty reservation station and an empty slot in the ROB, send the operands to the reservation station if they available in either the registers or the ROB for execution.

If either all reservations are full or the ROB is full, then instruction issue is stalled until both have available entries. This stage is sometimes called dispatch in a dynamically scheduled processor. Execute —If one or more of the operands is not yet available, monitor the CDB common data bus while waiting for the register to be computed. When both operands are available at a reservation station, execute the operation. If the value to be stored is not available yet, the CDB must be monitored until that value is broadcast, at which time the Value field of the ROB entry of the store is updated.

Commit —There are three different sequences of actions at commit depending on whether the committing instruction is: a branch with an incorrect prediction, a store, or any other instruction normal commit. The normal commit case occurs when an instruction reaches the head of the ROB and its result is present in the buffer; at this point, the processor updates the register with the result and removes the instruction from the ROB. Committing a store is similar except that memory is updated rather than a result register.

When a branch with incorrect prediction reaches the head of the ROB, it indicates that the speculation was wrong. The ROB is flushed and execution is restarted at the correct successor of the branch.

Follow us:. Share this page:. Hardware-Software Contracts for Secure Speculation. Best Paper Award. Performances are based on these code sequences. It is used in dynamic scheduling.

And it is not rely on any code series as like software. It does not require any code series to execute highly for the hardware. Software — Software requires code sequence as it is very important not like hardware. Distinguish between hardware versus software speculation mechanisms? Please reply the answer as soon as possible? Thanking you. Awaiting for your response. Go To Solution. Best Answer. You can use different implementation on single architecture.