Single cycle context switching by swapping a primary latch value and a selected secondary latch value in a register file
View Patent ↗A register file bit includes a primary latch and a secondary latch with a feedback path and a context switch mechanism that allows a fast context switch when execution changes from one thread to the next. A bit value for a second thread of execution is stored in the primary latch, then transferred to the secondary latch. The bit value for a first thread of execution is then written to the primary latch. When a context switch is needed (when the first thread stalls and the second thread needs to begin execution), the register file bit can perform a context switch from the first thread to the second thread in a single clock cycle. The register file bit contains a backup latch inside the register file itself so that minimal extra wire paths are needed to or from the existing register file.
1. A method for performing a fast context switch in a register file that includes a primary latch and a plurality of secondary latches having data outputs, the method comprising the steps of:
(A) for a selected one secondary latch of the plurality of secondary latches, performing the steps of A1 and A2:
(A1) storing a first value in the primary latch that corresponds to a selected thread;
(A2) moving the first value in the primary latch to the selected one of the plurality of secondary latches;
(B) storing a second value in the primary latch that corresponds to an active thread, where the active thread is different than the selected thread;
(C) selecting a data output of the selected one secondary latch only from among each of the data outputs of the secondary latches for performing the context switch with the primary latch; and
(D) performing the context switch in a single clock cycle between the primary latch and the selected one secondary latch that causes the second value in the primary latch to be stored in the selected one secondary latch, and that causes the first value in the selected one secondary latch to be stored in the primary latch.