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MPC8240 Integrated Processor User’s Manual
Instruction Timing
The MPC8240 TLBs are 64-entry, two-way set-associative caches that contain instruction
and data address translations. The processor core provides hardware assist for software
table search operations through the hashed page table on TLB misses. Supervisor software
can invalidate TLB entries selectively.
After an effective address is generated, the higher-order bits of the effective address are
translated by the appropriate MMU into physical address bits. Simultaneously, the
lower-order address bits (that are untranslated; therefore, considered both logical and
physical), are directed to the on-chip caches where they form the index into the four-way
set-associative tag array. After translating the address, the MMU passes the higher-order
bits of the physical address to the cache, and the cache lookup completes. For
caching-inhibited accesses or accesses that miss in the cache, the untranslated lower-order
address bits are concatenated with the translated higher-order address bits; the resulting
32-bit physical address is then used by the system interface, which accesses external
memory.
For instruction accesses, the MMU performs an address lookup in both the 64 entries of the
ITLB, and in the IBAT array. If an effective address hits in both the ITLB and the IBAT
array, the IBAT array translation takes priority. Data accesses cause a lookup in the DTLB
and DBAT array for the physical address translation. In most cases, the physical address
translation resides in one of the TLBs and the physical address bits are readily available to
the on-chip cache.
When the physical address translation misses in the TLBs, the processor core provides
hardware assistance for software to search the translation tables in memory. When a
required TLB entry is not found in the appropriate TLB, the processor vectors to one of the
three TLB miss exception handlers so that the software can perform a table search operation
and load the TLB. When this occurs, the processor automatically saves information about
the access and the executing context. Refer to the MPC603e User’s Manual for more
detailed information about these features and the suggested software routines for searching
the page tables.
5.7 Instruction Timing
The processor core is a pipelined superscalar processor. A pipelined processor is one in
which the processing of an instruction is broken into discrete stages. Because the
processing of an instruction is broken into a series of stages, an instruction does not require
the entire resources of an execution unit at one time. For example, after an instruction
completes the decode stage, it can pass on to the next stage, while the subsequent
instruction can advance into the decode stage. This improves the throughput of the
instruction flow. The instruction pipeline in the processor core has four major stages,
described as follows:
Summary of Contents for MPC8240
Page 1: ...MPC8240UM D Rev 1 1 2001 MPC8240 Integrated Processor User s Manual ...
Page 38: ...xviii MPC8240 Integrated Processor User s Manual TABLES Table Number Title Page Number ...
Page 48: ...xlviii MPC8240 Integrated Processor User s Manual Acronyms and Abbreviations ...
Page 312: ...6 94 MPC8240 Integrated Processor User s Manual ROM Flash Interface Operation ...
Page 348: ...7 36 MPC8240 Integrated Processor User s Manual PCI Host and Agent Modes ...
Page 372: ...8 24 MPC8240 Integrated Processor User s Manual DMA Register Descriptions ...
Page 394: ...9 22 MPC8240 Integrated Processor User s Manual I2O Interface ...
Page 412: ...10 18 MPC8240 Integrated Processor User s Manual Programming Guidelines ...
Page 454: ...12 14 MPC8240 Integrated Processor User s Manual Internal Arbitration ...
Page 466: ...13 12 MPC8240 Integrated Processor User s Manual Exception Latencies ...
Page 516: ...16 14 Watchpoint Trigger Applications ...
Page 538: ...B 16 MPC8240 Integrated Processor User s Manual Setting the Endian Mode of Operation ...
Page 546: ...C 8 MPC8240 Integrated Processor User s Manual ...
Page 640: ...INDEX Index 16 MPC8240 Integrated Processor User s Manual ...