参数资料
型号: RM5261A-300H
厂商: PMC-SIERRA INC
元件分类: 微控制器/微处理器
英文描述: 64-BIT, 300 MHz, MICROPROCESSOR, PQFP208
封装: HEAT SPREADER, MQFP-208
文件页数: 11/42页
文件大小: 898K
代理商: RM5261A-300H
Proprietary and Confidential to PMC-Sierra, Inc and for its Customer’s Internal Use
19
Document ID: PMC-2002240, Issue 1
RM5261A Microprocessor with 64-Bit System Bus Data Sheet
Preliminary
occurs on an instruction address translation by the ITLB, the least-recently used ITLB entry is
filled from the JTLB. The operation of the ITLB is completely transparent to the user.
3.16 Data TLB
The RM5261A implements a 4-entry data TLB (DTLB) for the same reasons cited above for the
ITLB. Each DTLB entry maps a 4 KB page. The DTLB improves performance by allowing data
address translation to occur in parallel with instruction address translation. When a miss occurs on
a data address translation by the DTLB, the DTLB is filled from the JTLB. The DTLB refill is
pseudo-LRU: the least recently used entry of the least recently used pair of entries is filled. The
operation of the DTLB is completely transparent to the user.
3.17 Cache Memory
The RM5261A incorporates on-chip instruction and data caches that can be accessed in a single
processor cycle. Each cache has its own 64-bit data path and both caches can be accessed
simultaneously. The cache subsystem provides the integer and floating-point units with an
aggregate bandwidth of 3.2 GB per second at an internal clock frequency of 200 MHz.
3.18 Instruction Cache
The RM5261A incorporates a two-way set associative on-chip instruction cache. This virtually
indexed, physically tagged cache is 32 KB in size and is protected with word parity.
Since the cache is virtually indexed, the virtual-to-physical address translation occurs in parallel
with the cache access, further increasing performance by allowing these two operations to occur
simultaneously. The cache tag contains a 24-bit physical address, a valid bit, and a single parity bit.
The instruction cache is 64-bits wide and can be accessed each processor cycle. Accessing 64 bits
per cycle allows the instruction cache to supply two instructions per cycle to the superscalar
dispatch unit. For typical code sequences where a floating-point load or store and a floating-point
computation instruction are being issued together in a loop, the entire bandwidth available from
the instruction cache is consumed.
Cache miss refill writes 64 bits per cycle to minimize the cache miss penalty. The line size is eight
instructions (32 bytes) to maximize the performance of communication between the processor and
the memory system.
The RM5261A supports cache locking. The contents of set A of the cache can be locked by setting
a bit in the coprocessor 0 Status register. Locking the set prevents its contents from being
overwritten by a subsequent cache miss. Refills occur only into set B. This mechanism allows the
programmer to lock critical code into the cache, thereby guaranteeing deterministic behavior for
the locked code sequence.
3.19 Data Cache
For fast, single cycle data access, the RM5261A includes a 32 KB on-chip data cache that is two-
way set associative with a fixed 32-byte (eight words) line size.
The data cache is protected with byte parity and its tag is protected with a single parity bit. It is
virtually indexed and physically tagged to allow simultaneous address translation and data cache
access.
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