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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
60 of 808
NXP Semiconductors
UM10360
Chapter 5: LPC17xx Flash accelerator
2.2 Flash programming Issues
Since the flash memory does not allow accesses during programming and erase
operations, it is necessary for the flash accelerator to force the CPU to wait if a memory
access to a flash address is requested while the flash memory is busy with a
programming operation. Under some conditions, this delay could result in a Watchdog
time-out. The user will need to be aware of this possibility and take steps to insure that an
unwanted Watchdog reset does not cause a system failure while programming or erasing
the flash memory.
In order to preclude the possibility of stale data being read from the flash memory, the
LPC17xx flash accelerator buffers are automatically invalidated at the beginning of any
flash programming or erase operation. Any subsequent read from a flash address will
cause a new fetch to be initiated after the flash operation has completed.
3.
Register description
The flash accelerator is controlled by the register shown in
. More detailed
descriptions follow.
[1]
Reset Value reflects the data stored in defined bits only. It does not include reserved bits content.
4.
Flash Accelerator Configuration register (FLASHCFG - 0x400F C000)
Configuration bits select the flash access time, as shown in
The lower bits of
FLASHCFG control internal flash accelerator functions and should not be altered.
Following reset, flash accelerator functions are enabled and flash access timing is set to a
default value of 6 clocks.
Changing the FLASHCFG register value causes the flash accelerator to invalidate all of
the holding latches, resulting in new reads of flash information as required. This
guarantees synchronization of the flash accelerator to CPU operation.
Table 48.
Summary of flash accelerator registers
Name
Description
Access Reset
value
Address
FLASHCFG
Flash Accelerator Configuration Register.
Controls flash access timing. See
.
R/W
0x303A 0x400F C000
Table 49.
Flash Accelerator Configuration register (FLASHCFG - address 0x400F C000) bit description
Bit
Symbol
Value Description
Reset
value
11:0
-
-
Reserved, user software should not change these bits from the reset value.
0x03A