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18522F/0—Jan1997 AMD-K5 Processor Data Sheet

PRELIMINARY INFORMATION

while the data cycle continues. Assertion of HOLD can occur at

any time, but HLDA will not be asserted until pending cycles

are completed.

To avoid excessive power drain, AHOLD should not be negated

when BRDY is asserted during a write cycle, and when ADS is

asserted at the beginning of a writeback cycle.

Use of BOFF BOFF causes the processor to float its local bus on the next

clock cycle and to terminate the current bus cycle (see Figure

7). BOFF is sampled every clock cycle. If both BOFF and BRDY

are asserted during the same clock cycle, BRDY is ignored and

the associated data transfer must be re-initiated. If BOFF is

asserted while ADS is asserted, the processor floats ADS, even

though it is in its asserted state. This situation must not be

interpreted as the start of a cycle by the system.

Figure 7. BOFF Timing

KEN must be reasserted by the system to enable caching on

any cycle that was previously aborted by BOFF. If a burst cycle

is aborted by the assertion of BOFF in the middle of the access,

the initial state of KEN when the access began will be used

when the cycle is restarted. KEN should be reasserted if cach-

ing is enabled for the cycle.

Any cycles aborted due to BOFF are recorded behind a pend-

ing writeback cycle that is scheduled in response to a snoop hit

to a modified line. For example, if a cache line fill is aborted

due to BOFF, and an external cycle hits a modified line, the

cache line fill is completed after the modified line is written

back.

CLK

ADS

BOFF

Data

…

Add/

Control

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AMD K5 Manual do Utilizador Página 51