SN260 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'SN260' PDF : 88 Pages View PDF
Functional description
SN260
5.6.1
5.6.2
Simulated EEPROM
The protocol stack reserves a section of Flash memory to provide simulated EEPROM
storage area for stack and customer tokens. The Flash cell has been qualified for a data
retention time of >100 years at room temperature and is rated to have a guaranteed 1,000
write/erase cycles. Because the Flash cells are qualified for up to 1,000 write cycles, the
simulated EEPROM implements an effective wear-leveling algorithm which effectively
extends the number of write cycles for individual tokens.
The number of set-token operations is finite due to the write cycle limitation of the Flash. It is
not possible to guarantee an exact number of set-token operations because the life of the
simulated EEPROM depends on which tokens are written and how often.
The SN260 stores non-volatile information necessary for network operation as well as 8
tokens available to the Host (see section Section 7.2.6: Tokens on page 37). The majority of
internal tokens are only written when the SN260 performs a network join or leave operation.
As a simple estimate of possible set-token operations, consider an SN260 in a stable
network (no joins or leaves) not sending any messages where the Host uses only one of the
8-byte tokens available to it. Under this scenario, a very rough estimate results in
approximately 330,000 possible set-token operations. The number of possible set-token
calls, though, depends on which tokens are being set, so the ratios of set-token calls for
each token plays a large factor. A very rough estimate for the total number of times an App
token can be set is approximately 320,000.
These estimates would typically increase if the SN260 is kept closer to room temperature,
since the 1,000 guaranteed write cycles of the Flash is for across temperature.
Flash information area (FIA)
The SN260 also includes a separate 1024-byte FIA that can be used for storage of data
during manufacturing, including serial numbers and calibration values. Programming of this
special Flash page can only be enabled using the SIF interface to prevent accidental
corruption or erasure. The EmberZNet stack reserves a small portion of this space for its
own use and in addition makes eight manufacturing tokens available to the application. See
Section 7.2.6: Tokens on page 37, for more information.
5.7
Encryption accelerator
The SN260 contains a hardware AES encryption engine that is attached to the CPU using a
memory-mapped interface. NIST-based CCM, CCM*, CBC-MAC, and CTR modes are
implemented in hardware. These modes are described in the IEEE 802.15.4-2003
specification, with the exception of CCM*, which is described in the ZigBee Security
Services Specification 1.0. The EmberZNet stack implements a security API for applications
that require security at the application level.
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