AMD-K6 Datasheet, PDF (122/346 Pages) Advanced Micro Devices – AMD-K6 Processor

AMD-K6^® Processor Data Sheet
Preliminary Information
20695H/0—March 1998
5.32
LOCK# (Bus Lock)
Output
Summary
The processor asserts LOCK# during a sequence of bus cycles to
ensure that the cycles are completed without allowing other bus
masters to intervene. Locked operations consist of two to five
bus cycles. LOCK# is asserted during the following operations:
s An interrupt acknowledge sequence
s Descriptor Table accesses
s Page Directory and Page Table accesses
s XCHG instruction
s An instruction with an allowable LOCK prefix
In order to ensure that locked operations appear on the bus and
are visible to the entire system, any data operands addressed
during a locked cycle that reside in the processor’s cache are
flushed and invalidated from the cache prior to the locked
operation. If the cache line is in the modified state, it is written
back and invalidated prior to the locked operation. Likewise,
any data read during a locked operation is not cached.
Driven and Floated
The processor ensures that LOCK# does not glitch.
During a locked cycle, LOCK# is asserted off the same clock
edge on which ADS# is asserted and remains asserted until the
last BRDY# of the last bus cycle is sampled asserted. The
processor negates LOCK# for at least one clock between
consecutive sequences of locked operations to allow the system
logic to arbitrate for the bus.
LOCK# is floated off the clock edge that BOFF# is sampled
asserted and off the clock edge that the processor asserts HLDA
in response to HOLD. When LOCK# is floated due to BOFF#
sampled asserted, the system logic is responsible for preserving
the lock condition while LOCK# is in the high-impedance state.
104
Signal Descriptions
Chapter 5