UM10850
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User manual
Rev. 2.4 — 13 September 2016
45 of 464
NXP Semiconductors
UM10850
Chapter 4: LPC5410x System configuration (SYSCON)
4.5.33 Flash configuration register
Depending on the system clock frequency, access to the flash memory can be configured
with various access times by writing to the FLASHCFG register. It is recommended to use
the set_voltage Power API (see
) to configure device operation in order to
achieve lower power operation. However, flash timing can also be set up by user software
as shown in the table.
Enabling buffering, acceleration, and prefetch will substantially improve performance.
Buffering saves power by allowing previously accessed information to be reused without a
flash read. Acceleration saves power by reducing CPU stalls. Prefetch typically has a
small power cost due to some flash reads being performed that ultimately are not needed
Remark:
Improper setting of this register may result in incorrect operation of the flash
memory. Do not change the flash access time when using the power API in low-power
mode.
Table 62.
Flash configuration register (FLASHCFG, main syscon: address 0x4000 0124) bit description
Bit
Symbol
Value
Description
Reset
value
1:0
FETCHCFG
Instruction fetch configuration. This field determines how flash accelerator buffers are
used for instruction fetches.
0x2
00
Instruction fetches from flash are not buffered. Every fetch request from the CPU
results in a read of the flash memory. This setting may use significantly more power
than when buffering is enabled.
01
One buffer is used for all instruction fetches.
10
All buffers may be used for instruction fetches.
11
Reserved setting, do not use.
3:2
DATACFG
Data read configuration. This field determines how flash accelerator buffers are used
for data accesses.
0x2
00
Data accesses from flash are not buffered. Every data access from the CPU results
in a read of the flash memory.
01
One buffer is used for all data accesses.
10
All buffers may be used for data accesses.
11
Reserved setting, do not use.
4
ACCEL
Acceleration enable.
1
0
Flash acceleration is disabled. Every flash read (including those fulfilled from a
buffer) takes FL 1 system clocks. This allows more determinism at a cost
of performance.
1
Flash acceleration is enabled. Performance is enhanced, dependent on other
FLASHCFG settings.
5
PREFEN
Prefetch enable.
0
0
No instruction prefetch is performed.
1
If the FETCHCFG field is not 0, the next flash line following the current execution
address is automatically prefetched if it is not already buffered.
6
PREFOVR
Prefetch override. This bit only applies when PREFEN = 1 and a buffered instruction
is completing for which the next flash line is not already buffered or being prefetched.
0
0
Any previously initiated prefetch will be completed.
1
Any previously initiated prefetch will be aborted, and the next flash line following the
current execution address will be prefetched if not already buffered.