MPLAB C Compiler for PIC24 MCUs and dsPIC DSCs ... - Microchip

6.3 PMP POINTERS
Additional C Pointer Types
• auto_psv - the compiler will set the PSVPAG register to the correct value for
accessing the auto_psv space, ensuring that it is restored when exiting the ISR
• no_auto_psv - the compiler will not set the PSVPAG register
For example:
void __attribute__((interrupt, no_auto_psv)) _T1Interrupt(void) {
IFS0bits.T1IF = 0;
}
Current code (that does not assert the auto_psv attribute) may not execute properly
unless recompiled. When recompiled, if no indication is made, the compiler will generate
a warning message and select the auto_psv model.
The choice is provided so that, if you are especially conscious of interrupt latency, you
may select the best option. Saving and setting the PSVPAG will consume approximately
3 cycles at the entry to the function and one further cycle to restore the setting
upon exit from the function.
Note that boot or secure interrupt service routines will use a different setting of the
PSVPAG register for their constant data.
Some devices contain a Parallel Master Port (PMP) peripheral which allows the connection
of various memory and non-memory devices directly to the device. Access to
the peripheral is controlled via a selection of peripherals. More information about this
peripheral can be found in the Family Reference Manual or device-specific data sheets.
PMP pointers are similar to managed PSV pointers as described in the previous section.
These pointers make it easier to read or write data using the PMP.
The peripheral can require a substantial amount of configuration, depending upon the
type and brand of memory device that is connected. This configuration is not done
automatically by the compiler.
The extensions presented here allow the definition of a variable as PMP. This means
that the compiler will communicate with the PMP peripheral in order to access the variable.
To use this feature:
• Initialize PMP - define the initialization function: void __init_PMP(void)
• Declare a New Memory Space
• Define Variables within PMP Space
6.3.1 Initialize PMP
The PMP peripheral requires initialization before any access can be properly processed.
Consult the appropriate documentation for the device you are interfacing to
and the data sheet for 16-bit device you are using.
The toolsuite, if PMP is used, will call void __init_PMP(void) during normal C
run-time initialization. If a customized initialization is being used, please ensure that this
function is called.
This function should make the necessary settings in the PMMODE and PMCON SFRs.
In particular:
• The peripheral should not be configured to generate interrupts:
PMMODEbits.IRQM = 0
• The peripheral should not be configured to generate increments:
PMMODEbits.INCM = 0
The compiler will modify this setting during run-time as needed.
© 2008 Microchip Technology Inc. DS51284H-page 83