BL4S100 User’s Manual
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4.4.6 SRAM Use
The BL4S100 has a battery-backed data SRAM and a program-execution SRAM.
Dynamic C provides the
protected
keyword to identify variables that are to be placed
into the battery-backed SRAM. The compiler generates code that maintains two copies of
each protected variable in the battery-backed SRAM. The compiler also generates a flag to
indicate which copy of the protected variable is valid at the current time. This flag is also
stored in the battery-backed SRAM. When a protected variable is updated, the “inactive”
copy is modified, and is made “active” only when the update is 100% complete. This
assures the integrity of the data in case a reset or a power failure occurs during the update
process. At power-on the application program uses the active copy of the variable pointed
to by its associated flag.
The sample code below shows how a protected variable is defined and how its value can
be restored.
protected nf_device nandFlash;
int main() {
...
_sysIsSoftReset(); // restore any protected variables
The
bbram
keyword may also be used instead if there is a need to store a variable in bat-
tery-backed SRAM without affecting the performance of the application program. Data
integrity is
not
assured when a reset or power failure occurs during the update process.
Additional information on
bbram
and
protected
variables is available in the
Dynamic C
User’s Manual
.
