PowerPC e500 Core Family Reference Manual, Rev. 1
4-26
Freescale Semiconductor
Execution Timing
The instruction and data caches are integrated with the LSU, instruction unit, and core interface
unit in the memory subsystem of the core complex as shown in
Figure 4-10
.
Figure 4-10. Cache/Core Interface Unit Integration
When free of data dependencies, cacheable loads execute in the LSU in a speculative manner with
a maximum throughput of one per cycle and a total 3-cycle latency for integer loads. Data returned
from the cache on a load is held in a rename buffer until the completion logic commits the value
to the processor state.
Table 4-1. Load and Store Queues
Queue
Description
LSU store
queue
Stores cannot execute speculatively and are held in the seven-entry store queue, shown in
Figure 4-10
, until
completion logic indicates that the store instruction is to be committed. The store queue arbitrates for L1 data cache
access. When arbitration succeeds, data is written to the data cache and the store is removed from the store queue.
If a store is caching-inhibited, the operation moves through the store queue to the rest of the memory subsystem.
LSU L1
load miss
queue
(LMQ)
As loads reach the LSU, it tries to access the cache. On a hit, the cache returns the data. If there is a miss, the LSU
allocates an LMQ entry and a DLFB entry. The LSU then queues a bus transaction to read the line. If a subsequent
load hits, the cache returns the results. If a subsequent load misses, the LSU allocates a second LMQ entry and, if
the load is to a different cache line than the outstanding miss, it allocates the second DLFB entry and queues a
second read transaction on the bus. If the load miss is to the same cache line as an outstanding miss, the LSU need
not allocate a new DLFB entry.
The LSU continues processing load hits and load misses until one of the following conditions occurs:
• The LMQ is full and another load miss occurs.
• The LSU tries to perform a load miss, all of the DLFB entries are full, and the load is not to any of the cache lines
that are represented in the DLFB.
Instruction
MMU
4
Load Miss
Queue
Data
MMU
Core Complex Bus
L1 Store
Queue
Core Interface Unit
I-Cache
Tags
I-Cache
Status
I-Cache
D-Cache
Tags
D-Cache
Status
D-Cache
8 instructions
(cache block)
DWB
1–4
instructions
forwarded on
cache miss
8-byte
LSU Queues
ILFB
I-Cache
DLFB
instructions
Queues
(LMQ)
Up to a
double
word
forwarded
32-byte
(8 word)
on a
cache
miss
Instruction Unit
Load/Store Unit
e500v1
e500v2
e500v1
e500v2
Содержание PowerPC e500 Core
Страница 1: ...PowerPC e500 Core Family Reference Manual Supports e500v1 e500v2 E500CORERM Rev 1 4 2005...
Страница 36: ...PowerPC e500 Core Family Reference Manual Rev 1 xxxvi Freescale Semiconductor...
Страница 38: ...PowerPC e500 Core Family Reference Manual Rev 1 Part I 2 Freescale Semiconductor...
Страница 316: ...PowerPC e500 Core Family Reference Manual Rev 1 7 18 Freescale Semiconductor Performance Monitor...
Страница 332: ...PowerPC e500 Core Family Reference Manual Rev 1 Part II 2 Freescale Semiconductor...
Страница 362: ...PowerPC e500 Core Family Reference Manual Rev 1 10 26 Freescale Semiconductor Auxiliary Processing Units APUs...
Страница 440: ...PowerPC e500 Core Family Reference Manual Rev 1 A 8 Freescale Semiconductor Programming Examples...
Страница 444: ...PowerPC e500 Core Family Reference Manual Rev 1 B 4 Freescale Semiconductor Guidelines for 32 Bit Book E...
Страница 530: ...Opcode Listings PowerPC e500 Core Family Reference Manual Rev 1 D 50 Freescale Semiconductor...
Страница 534: ...PowerPC e500 Core Family Reference Manual Rev 1 E 4 Freescale Semiconductor Revision History...