User`s manual

User’s Manual 31
5.2 Dynamic C Function Calls
5.2.1 Digital I/O
The RCM3200 was designed to interface with other systems, and so there are no drivers
written specifically for the I/O. The general Dynamic C read and write functions allow
you to customize the parallel I/O to meet your specific needs. For example, use
WrPortI(PEDDR, &PEDDRShadow, 0x00);
to set all the Port E bits as inputs, or use
WrPortI(PEDDR, &PEDDRShadow, 0xFF);
to set all the Port E bits as outputs.
When using the auxiliary I/O bus on the Rabbit 3000 chip, add the line
#define PORTA_AUX_IO // required to enable auxiliary I/O bus
to the beginning of any programs using the auxiliary I/O bus.
The sample programs in the Dynamic C SAMPLES/RCM3200 directory provide further
examples.
5.2.2 SRAM Use
The RCM3200 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.