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11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
19.4.2
Read Operations
An optimized controller manages embedded Flash reads, thus increasing performance when the
processor is running in Thumb2 mode by means of the 128- or 64- bit wide memory interface.
The Flash memory is accessible through 8-, 16- and 32-bit reads.
As the Flash block size is smaller than the address space reserved for the internal memory area,
the embedded Flash wraps around the address space and appears to be repeated within it.
The read operations can be performed with or without wait states. Wait states must be pro-
grammed in the field FWS (Flash Read Wait State) in the Flash Mode Register (EEFC_FMR).
Defining FWS to be 0 enables the single-cycle access of the embedded Flash. Refer to the Elec-
trical Characteristics for more details.
19.4.2.1
128-bit or 64-bit Access Mode
By default the read accesses of the Flash are performed through a 128-bit wide memory inter-
face. It enables better system performance especially when 2 or 3 wait state needed.
For systems requiring only 1 wait state, or to privilege current consumption rather than perfor-
mance, the user can select a 64-bit wide memory access via the FAM bit in the Flash Mode
Register (EEFC_FMR)
Please refer to the electrical characteristics section of the product datasheet for more details.
19.4.2.2
Code Read Optimization
This feature is enabled if the EEFC_FMR register bit SCOD is cleared.
A system of 2 x 128-bit or 2 x 64-bit buffers is added in order to optimize sequential Code Fetch.
Note:
Immediate consecutive code read accesses are not mandatory to benefit from this optimization.
The sequential code read optimization is enabled by default. If the bit SCODIS in Flash Mode
Register (EEFC_FMR) is set to 1, these buffers are disabled and the sequential code read is not
optimized anymore.
Another system of 2 x 128-bit or 2 x 64-bit buffers is added in order to optimize loop code fetch.
When a backward jump is inserted in the code, the pipeline of the sequential optimization is bro-
ken, and it becomes inefficient. In this case the loop code read optimization takes over from the
sequential code read optimization to avoid insertion of wait states. The loop code read optimiza-
tion is enabled by default. If in Flash Mode Register (EEFC_FMR), the bit CLOE is reset to 0 or
the bit SCODIS is set to 1, these buffers are disabled and the loop code read is not optimized
anymore.
Содержание SAM4S Series
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