EXTERNAL BUS
14-30
14.2.7
Atomic Bus Transactions
The atomic instructions,
atadd and atmod
, consist of a load and store request to the same memory
location. Atomic instructions require indivisible, read-modify-write access to memory. That is,
another bus agent must not access the target of the atomic instruction between read and write
cycles. Atomic instructions are necessary to implement software semaphores.
For atomic bus accesses, the 80960Jx processor asserts the LOCK pin during the first Ta of the
read operation and deasserts LOCK in the last data transfer of the write operation. LOCK is
deasserted at the same clock edge that BLAST is asserted. The i960Jx processor does not assert
LOCK except while a read-modify-write operation is in progress. While LOCK is asserted, the
processor can perform other, non-atomic, accesses such as fetches. However, the 80960Jx
processor will not acknowledge HOLD requests. This behavior is an enhancement over earlier
i960 microprocessors.
Figure 14-17
illustrates locked read/write accesses associated with an
atomic instruction.
Содержание i960 Jx
Страница 1: ...Release Date December 1997 Order Number 272483 002 i960 Jx Microprocessor Developer s Manual ...
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Страница 25: ...1 INTRODUCTION ...
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Страница 35: ...2 DATA TYPES AND MEMORY ADDRESSING MODES ...
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Страница 47: ...3 PROGRAMMING ENVIRONMENT ...
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Страница 73: ...4 CACHE AND ON CHIP DATA RAM ...
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Страница 85: ...5 INSTRUCTION SET OVERVIEW ...
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Страница 111: ...6 INSTRUCTION SET REFERENCE ...
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Страница 195: ...INSTRUCTION SET REFERENCE 6 83 6 Opcode mov 5CCH REG movl 5DCH REG movt 5ECH REG movq 5FCH REG See Also LOAD STORE lda ...
Страница 233: ...7 PROCEDURE CALLS ...
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Страница 257: ...8 FAULTS ...
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Страница 291: ...9 TRACING AND DEBUGGING ...
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Страница 309: ...10 TIMERS ...
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Страница 325: ...11 INTERRUPTS ...
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Страница 369: ...12 INITIALIZATION AND SYSTEM REQUIREMENTS ...
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Страница 413: ...13 MEMORY CONFIGURATION ...
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Страница 429: ...14 EXTERNAL BUS ...
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Страница 469: ...15 TEST FEATURES ...
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Страница 493: ...A CONSIDERATIONS FOR WRITING PORTABLE CODE ...
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Страница 503: ...B OPCODES AND EXECUTION TIMES ...
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Страница 515: ...C MACHINE LEVEL INSTRUCTION FORMATS ...
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Страница 523: ...D REGISTER AND DATA STRUCTURES ...
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Страница 551: ...GLOSSARY ...
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Страница 561: ...INDEX ...
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