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

MPLAB C Compiler for PIC18 MCUs vs. 16-Bit Devices
D.14 MEMORY MODELS
EXAMPLE D-7: LOCATE THE FUNCTION PRINTSTRING AT ADDRESS
0X8000 IN PROGRAM MEMORY
PIC18 #pragma code myTextSection=0x8000;
int PrintString(const char *s){...};
16-Bit int __attribute__((address(0x8000))) PrintString
(const char *s) {...};
EXAMPLE D-8: COMPILER AUTOMATICALLY SAVES AND RESTORES THE
VARIABLES VAR1 AND VAR2
The PIC18 MCU Compiler uses non-ANSI small and large memory models. Small uses
the 16-bit pointers and restricts program memory to be less than 64 KB (32 KB words).
The 16-Bit Device Compiler uses non-ANSI small code and large code models. Small
code restricts program memory to be less than 96 KB (32 KB words). In large code,
pointers may go through a jump table.
D.15 CALLING CONVENTIONS
D.16 STARTUP CODE
PIC18 #pragma interrupt isr0 save=var1, var2
void isr0(void)
{
/* perform interrupt function here */
}
16-Bit void __attribute__((__interrupt__(__save__(var1,var2))))
isr0(void)
{
/* perform interrupt function here */
}
There are many differences in the calling conventions of the MPLAB C Compiler for
PIC18 MCUs and the MPLAB C Compiler for PIC24 MCUs and dsPIC ® DSCs. Please
refer to Section 4.11 “Function Call Conventions” for a discussion of 16-Bit Device
Compiler calling conventions.
The PIC18 MCU Compiler provides three startup routines – one that performs no user
data initialization, one that initializes only variables that have initializers, and one that
initializes all variables (variables without initializers are set to zero as required by the
ANSI standard).
The 16-Bit Device Compiler provides two startup routines – one that performs no user
data initialization and one that initializes all variables (variables without initializers are
set to zero as required by the ANSI standard) except for variables in the persistent data
section.
D.17 COMPILER-MANAGED RESOURCES
The PIC18 MCU Compiler has the following managed resources: PC, WREG, STA-
TUS, PROD, section .tmpdata, section MATH_DATA, FSR0, FSR1, FSR2, TBLPTR,
TABLAT.
The 16-Bit Device Compiler has the following managed resources: W0-W15, RCOUNT,
SR.
© 2008 Microchip Technology Inc. DS51284H-page 207