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Prefetch
Buffer 0
Prefetch
Buffer 1
Prefetch
Buffer 2
Prefetch
Buffer 3
0
WORD 7
WORD 6
WORD 5
WORD 4
WORD 3
WORD 2
WORD 1
WORD 0
WORD 6
WORD 5
WORD 4
WORD 3
WORD 2
WORD 1
WORD 0
WORD 7
255
127
96 95
64 63
32 31
128
159
160
191
192
223
224
WORD 7
WORD 6
WORD 5
WORD 4
WORD 3
WORD 2
WORD 1
WORD 0
WORD 6
WORD 5
WORD 4
WORD 3
WORD 2
WORD 1
WORD 0
WORD 7
TAG
TAG
TAG
TAG
WAIT
STATES
1
2
3
4
5
6
7
EVENT A
EVENT B
EVENT C
EVENT D
Least
Recently
Used Buffer
Functional Description
538
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Internal Memory
Figure 7-7. Prefetch Fills From Flash
If the CPU target word is beyond word 2 (word 3 through word 7) then the next prefetch fill begins
immediately, and, depending on the CPU frequency, a delay is incurred between CPU access of word 7
and word 0 of the next line.
NOTE:
For optimal prefetch buffer performance, align application code and branches on 8-word
boundaries.
NOTE:
Because the prefetch buffers and flash memory can effectively be used at 20 MHz and
higher, an application can have an improvement in current consumption from 16 MHz to 20
MHz.
The prefetch buffers can be forced ON and OFF by setting the FPFON and FPFOFF bits in the Flash
Configuration (FLASHCONF) register at 0xFC8. If the application sets the FPFON or FPFOFF bit while
the CPU is currently reading or writing to flash, the prefetch buffer action of turning on or off happens only
after the flash operation has completed. This feature can be used in test modes when determining
optimum memory configuration for code.
Prefetch buffer valid tags can be cleared in the following ways:
•
Any Flash Configuration (FLASHCONF) register changes, such as:
–
Disabling the prefetch buffer by setting the FPFOFF bit
–
Setting the CLRTV bit to clear the prefetch buffer tags
•
A system reset
•
ROM accesses
•
Error during ICODE accesses
•
System aborts
•
Mirror mode changes
NOTE:
If the prefetch buffers are enabled and application code branches to a location other than
flash memory which then modifies the flash memory, the prefetch tags must be cleared
before returning to flash code execution. Prefetch buffer valid tags can be cleared by setting
the CLRTV bit in the FLASHCONF register.