|
80960HA Datasheet, PDF (72/102 Pages) Intel Corporation – 80960HA/HD/HT 32-Bit High-Performance Superscalar Processor | |||
|
◁ |
80960HA/HD/HT
Figure 49. BREQ and BSTALL Operation
CLKIN
ADS
BLAST
BREQ
BSTALL
The processor can stall (BSTALL asserted) even with an empty bus queue (BREQ deasserted).
Depending on the instruction stream and memory wait states, the two signals can be separated by
several CLKIN cycles.
Bus arbitration logic that logically âANDsâ BSTALL and BREQ will not correctly grant the bus to
the processor in all stall cases, potentially degrading processor performance.
Do not logically âANDâ BSTALL and BREQ together in arbitration logic. Instead, the simplest
bus arbitration should logically âORâ BSTALL and BREQ to determine the processorâs bus
ownership requirements.
More sophisticated arbitration should recognize the priority nature of these two signals. Using a
traffic light analogy, BREQ is a âyellow lightâ warning of a possible processor stall and BSTALL
is a âred lightâ indicating a stall in progress.
66
Advance Information Datasheet
|
▷ |