AMD-K6 datasheet(168/346 Pages) AMD

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150

Bus Cycles

Chapter 6

AMD-K6® Processor Data Sheet

20695H/0—March 1998

Preliminary Information

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

edg e . If BOFF# is sampl e d asserted, the pr oc ess o r

unconditionally aborts any cycles in progress and transitions to

a bus hold state. (See “BOFF# (Backoff)” on page 87.) Figure 58

on page 151 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.

AMD-K6 Datasheet(PDF) 168 Page - Advanced Micro Devices