6.18 System Interface Coherency
The SysGblPerf* signal is provided for systems implementing a relaxed consistency memory model. The external agent asserts this signal when all processor requests are globally performed, thereby allowing the processor to graduate SYNC instructions. The external agent negates this signal when some processor requests are not yet globally performed, thereby preventing the processor from graduating SYNC instructions.
To prevent a SYNC instruction from graduating, the external agent must negate the SysGblPerf* signal no later than the same SysClk cycle in which it issued the external completion response for a processor read or upgrade request which is not yet globally performed. Also, the external agent must negate the SysGblPerf* signal no later than two SysClk cycles after the address cycle of a processor double/single/partial-word write request which has not yet been globally performed.
The SysGblPerf* signal may be permanently asserted in systems implementing a sequential consistency memory model.
Copyright 1995, MIPS Technologies, Inc. -- 29 JAN 96
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