UM10413
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 1 — 16 December 2011
15 of 268
NXP Semiconductors
UM10413
MPT612 User manual
8.2.2 Instruction latches and data latches
The MAM treats code and data accesses separately. There is a 128-bit latch, a 15-bit
address latch, and a 15-bit comparator associated with each buffer (prefetch, branch trail,
and data). Each 128-bit latch holds 4 words (4 ARM instructions, or 8 Thumb instructions).
Also associated with each buffer are 32 4:1 multiplexers that select the requested word
from the 128-bit line.
Each data access that is not in the data latch causes a flash fetch of 4 words of data,
which are captured in the data latch. This speeds up sequential data operations, but has
little or no effect on random accesses.
8.2.3 Flash programming issues
Since the flash memory does not allow access during programming and erase operations,
the MAM must force the CPU to wait if a memory access to a flash address is requested
while the flash module is busy. Under some conditions, this delay can result in a watchdog
time-out. You must ensure that an unwanted watchdog reset does not cause a system
failure while programming or erasing the flash memory.
To preclude the possibility of stale data being read from the flash memory, the MPT612
MAM holding latches are automatically invalidated at the beginning of any flash
programming or erase operation. Any subsequent read from a flash address initiates a
new fetch after the flash operation has completed.
8.3 MAM
operating
modes
There are three MAM modes of operation defined, trading off performance for ease of
predictability:
Mode 0:
MAM off. All memory requests result in a flash read operation (see
,
note 2). No instruction prefetches are performed.
Fig 6.
Simplified block diagram of the Memory Accelerator Module (MAM)
aaa-000572
BUS
INTERFACE
BUFFERS
MEMORY ADDRESS
ARM LOCAL BUS
FLASH MEMORY
BANK