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

PRELIMINARY INFORMATION

Locked Operations A locked cycle, illustrated in Figure 8, uses the LOCK pin to

indicate that the processor is performing a read-modify-write,

and that both the read operation and write operation must be

allowed to complete as a combined operation. (See Figure 36,

40, and 42 beginning on page 78.)

Figure 8. Locked Cycles

When the program generates a locked access, the processor

first looks in the data cache. If the locked object is modified in

the cache, it is written back to memory and invalidated. It is

then accessed using a locked memory cycle. Since combined

operations can access misaligned objects, locked operations

can result in multiple writebacks, multiple locked reads, and

multiple locked writes. When unaligned locked operations are

performed, SCYC is asserted

LOCK during HOLD

and BOFF

An assertion of HOLD after a locked operation has initiated is

ignored by the processor until after the entire locked opera-

tion has completed. Following completion, HLDA is asserted.

If BOFF is asserted during the read portion of a locked access,

LOCK will float and the entire locked access will be restarted

after BOFF is negated. If BOFF is asserted during the write

portion of a locked access, LOCK will float and only the write

will be restarted after BOFF is negated.

LOCK Operations

during Inquire Cycles

Inquire cycles can be performed as usual during locked opera-

tions. Inquire cycles during atomic locked read and write oper-

ations are only allowed from the external inquire. No

writebacks will be seen because the processor has already

evicted the modified line.

CLK

ADS

BRDY

W/R

LOCK

Data

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AMD K5 Manual do Utilizador Página 52