
W O R K I N G W I T H T H E C P U
Caches and write buffer
128
Hardware Reference NS9215
The caches use pseudo-random or round-robin replacement, selected by the RR
bit in R1: Control register.
Cache lockdown registers enable control over which cache ways are used for
allocation on a linefill, providing a mechanism for both lockdown and
controlling cache pollution.
The DCache stores the Physical Address Tag (PA tag) corresponding to each
DCache entry in the tag RAM for use during cache line write-backs, in addition
to the virtual address tag stored in the tag RAM. This means that the MMU is
not involved in DCache write-back operations, which removes the possibility of
TLB misses to the write-back address.
Cache maintenance operations provide efficient invalidation of:
–
The entire DCache or ICache
–
Regions of the DCache or ICache
–
Regions of virtual memory
Cache maintenance operations also provide for efficient cleaning and
invalidation of:
–
The entire DCache
–
Regions of the DCache
–
Regions of virtual memory
The latter allows DCache coherency to be efficiently maintained when small
code changes occur; for example, for self-modifying code and changes to
exception vectors.
Write buffer
The write buffer is used for all writes to a noncachable bufferable region, write-
through region, and write misses to a write-back region. A separate buffer is
incorporated in the DCache for holding write-back data for cache line evictions or
cleaning of dirty cache lines.
The main write buffer has a 16-word data buffer and a four-address buffer.
The DCache write-back buffer has eight data word entries and a single address
entry.
The
MCR
drain write buffer instruction enables both write buffers to be drained
under software control.
The
MCR
wait -for-interrupt causes both write buffers to be drained, and the
ARM926EJ-S processor to be put into low-power state until an interrupt occurs.
Enabling the
caches
On reset, the ICache and DCache entries all are invalidated and the caches
disabled. The caches are not accessed for reads or writes. The caches are enabled
using the I, C, and M bits from the R1: Control register, and can be enabled
independently of one another.
Содержание NS9215
Страница 1: ...NS9215 Hardware Reference 90000847_C Release date 10 April 2008...
Страница 3: ......
Страница 4: ......
Страница 26: ...26 Hardware Reference NS9215...
Страница 44: ...P I N O U T 26 5 System clock 44 Hardware Reference NS9215 System clock drawing...
Страница 52: ...P I N O U T 26 5 Power and ground 52 Hardware Reference NS9215...
Страница 80: ...I O C O N T ROL M O D U L E Memory Bus Configuration register 80 Hardware Reference NS9215...
Страница 136: ...WOR KI N G W I TH T H E C P U Noncachable instruction fetches 136 Hardware Reference NS9215...
Страница 202: ...S Y S T E M C O N T RO L M OD U L E RTC Module Control register 202 Hardware Reference NS9215...
Страница 260: ...M E MO R Y C O N T ROL L E R StaticMemory Turn Round Delay 0 3 registers 260 Hardware Reference NS9215...
Страница 354: ...E X T E R N A L D M A DMA Peripheral Chip Select register 354 Hardware Reference NS9215...
Страница 362: ...A E S D AT A E N C R Y P T I O N D E C R Y P T I O N M O D U L E CCM mode 362 Hardware Reference NS9215...
Страница 384: ...I O HU B M OD UL E Module Direct Mode TX Data Last FIFO 384 Hardware Reference NS9215 31 March 2008...
Страница 414: ...S E R I A L C ON T RO L M O D U L E U ART UART Modem Status register 414 Hardware Reference NS9215...
Страница 446: ...S E R I A L C ON T RO L M O D U L E S PI SPI timing characteristics 446 Hardware Reference NS9215...
Страница 472: ...R E A L TI M E C L O C K M O D U L E General Status register 472 Hardware Reference NS9215...
Страница 512: ...TI M I NG Clock timing 512 Hardware Reference NS9215...
Страница 514: ...PA CKA GING Processor Dimensions 514 Hardware Reference NS9215 P r o c e s s o r D i m e n s i o n s...
Страница 515: ...PA CKA GING Processor Dimensions www digiembedded com 515...
Страница 516: ...PA CKA GING Processor Dimensions 516 Hardware Reference NS9215...