AMD AMD-K6-2/400 User Guide - Page 204
Bus Backoff BOFF
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Preliminary Information AMD-K6™-2E+ Embedded Processor Data Sheet 23542A/0-September 2000 Bus Backoff (BOFF#) BOFF# provides the fastest response among bus-hold inputs. Either the system logic or another bus master can assert BOFF# to gain control of the bus immediately. BOFF# is also used to resolve potential deadlock problems that arise as a result of inquire cycles. The processor samples BOFF# on every clock edge. If BOFF# is sampled asserted, the processor unconditionally aborts any cycles in progress and transitions to a bus hold state. (See "BOFF# (Backoff)" on page 102.) Figure 73 on page 183 shows a read cycle that is aborted when the processor samples BOFF# asserted even though BRDY# is sampled asserted on the same clock edge. The read cycle is restarted after BOFF# is sampled negated (KEN# must be in the same state during the restarted cycle as its state during the aborted cycle). During a BOFF#-initiated inquire cycle that hits a shared or exclusive line, the processor samples BOFF# negated and restarts any bus cycle that was aborted when BOFF# was asserted. If a BOFF#-initiated inquire cycle hits a modified line, the processor performs a writeback cycle before it restarts the aborted cycle. If the processor samples BOFF# asserted on the same clock edge that it asserts ADS#, ADS# is floated but the system logic may erroneously interpret ADS# as asserted. In this case, the system logic must properly interpret the state of ADS# when BOFF# is negated. 182 Bus Cycles Chapter 7