
EM358x
12
Rev. 0.4
2 ARM
®
Cortex™-M3 and Memory Modules
This chapter discusses the ARM
®
Cortex
TM
-M3 Microprocessor, and reviews the EM358x’s flash and RAM
memory modules as well as the Memory Protection Unit (MPU).
2.1 ARM
®
Cortex™-M3 Microprocessor
The EM358x integrates the ARM
®
Cortex
TM
-M3 microprocessor, revision r1p1, developed by ARM Ltd., making
the EM358x a true System-on-Chip solution. The ARM
®
Cortex
TM
-M3 is an advanced 32-bit modified Harvard
architecture processor that has separate internal program and data buses, but presents a unified program and
data address space to software. The word width is 32 bits for both the program and data sides. The ARM
®
Cortex
TM
-M3 allows unaligned word and half-word data accesses to support efficiently-packed data structures.
The ARM
®
Cortex
TM
-M3 clock speed is configurable to 6 MHz, 12 MHz, or 24 MHz. For normal operation 24 MHz
is preferred over 12 MHz due to improved performance for all applications and improved duty cycling for
applications using sleep modes. The 6 MHz operation can only be used when radio operations are not required
since the radio requires an accurate 12 MHz clock.
The ARM
®
Cortex
TM
-M3 in the EM358x has also been enhanced to support two separate memory protection
levels. Basic protection is available without using the MPU, but normal operation uses the MPU. The MPU allows
for protecting unimplemented areas of the memory map to prevent common software bugs from interfering with
software operation. The architecture could also allow for separation of the networking stack from the application
code using a fine granularity RAM protection module. Errant writes are captured and details are reported to the
developer to assist in tracking down and fixing issues.
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