CACHE AND ON-CHIP DATA RAM
4-6
The application program is responsible for synchronizing its own code modification and cache
invalidation. In general, a program must ensure that modified code space is not accessed until
modification and cache-invalidate are completed. To achieve cache coherency, instruction cache
contents should be invalidated after code modification is complete. The
icctl
instruction
invalidates the instruction cache for the i960 Jx processor. Alternately, legacy software can use the
sysctl
instruction.
4.5
DATA CACHE
The i960 JT processor features a 4 Kbyte direct-mapped data cache. The i960 JF and JD
processors feature a 2-Kbyte, direct-mapped cache that enhances performance by reducing the
number of data load and store accesses to external memory. The i960 JA processors have a 1 Kbyte
direct-mapped data cache. The cache is write-through and write-allocate. It has a line size of
4 words and each line in the cache has a valid bit. To reduce fetch latency on cache misses, each
word within a line also has a valid bit. Caches are managed through the
dcctl
instruction.
User settings in the memory region configuration registers LMCON0-1 and DLMCON determine
which data accesses are cacheable or non-cacheable based on memory region.
4.5.1
Enabling and Disabling the Data Cache
To cache data, two conditions must be met:
1.
The data cache must be enabled. A
dcctl
instruction issued with an enable data cache
message enables the cache. On reset or initialization, the data cache is always disabled and
all valid bits are cleared (set to zero).
2.
Data caching for a location must be enabled by the corresponding logical memory template,
or by the default logical memory template, when no other template applies. See
section 13.6, “Programming the Logical Memory Attributes” (pg. 13-8)
for more details on
logical memory templates.
When the data cache is disabled, all data fetches are directed to external memory. Disabling the
data cache is useful for debugging or monitoring a system. To disable the data cache, issue a
dcctl
with a disable data cache message. The enable and disable status of the data cache and various
attributes of the cache can be determined by a
dcctl
issued with a data-cache status message.
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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