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

16-Bit C Compiler User’s Guide
write_external32
void __write_external32(unsigned int address,
unsigned int memory_space,
unsigned long data)
Write 32 bits of data to external memory space memory_space starting from address
address. The compiler would like to call this function if trying to write a 32-bit sized
object, such as a long or float type.
write_external64
void __write_external64(unsigned int address,
unsigned int memory_space,
unsigned long long data)
Write 64 bits of data to external memory space memory_space starting from address
address. The compiler would like to call this function if trying to write a 64-bit sized
object, such as a long long or long double type.
6.4.4 An External Example
The following snippets of example come from a working example (in the Examples
folder.)
This example implements, using external memory, addressable bit memory. In this
case each bit is stored in real data memory, not off chip. The code will define an
external memory of 512 units and map accesses using the appropriate read and
write function to one of 64 bytes in local data memory.
First the external memory is defined:
extern unsigned int bit_memory
__attribute__((space(external(size(512)))));
Next appropriate read and write functions are defined. These functions will make use
of an array of memory that is reserved in the normal way.
static unsigned char real_bit_memory[64];
unsigned char __read_external8(unsigned int address,
unsigned int memory_space) {
if (memory_space == bit_memory) {
/* an address within our bit memory */
unsigned int byte_offset, bit_offset;
byte_offset = address / 8;
bit_offset = address % 8;
return (real_bit_memory[byte_offset] >> bit_offset) & 0x1;
} else {
fprintf(stderr,"I don't know how to access memory space: %d\n",
memory_space);
}
return 0;
}
void __write_external8(unsigned int address,
unsigned int memory_space,
unsigned char data) {
if (memory_space == bit_memory) {
/* an address within our bit memory */
unsigned int byte_offset, bit_offset;
byte_offset = address / 8;
bit_offset = address % 8;
real_bit_memory[byte_offset] &= (~(1