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

16-Bit C Compiler User’s Guide
__builtin_clr
Assembler Operator
/ Machine
Instruction:
clr
Error Messages An error message will be displayed if the result is not an accumulator
register.
__builtin_clr_prefetch
Description: Clear an accumulator and prefetch data ready for a future MAC
operation.
xptr may be null to signify no X prefetch to be performed, in which
case the values of xincr and xval are ignored, but required.
yptr may be null to signify no Y prefetch to be performed, in which
case the values of yincr and yval are ignored, but required.
xval and yval nominate the address of a C variable where the
prefetched value will be stored.
xincr and yincr may be the literal values: -6, -4, -2, 0, 2, 4, 6 or an
integer value.
If AWB is non null, the other accumulator will be written back into the
referenced variable.
For example:
register int result asm("A");
int x_memory_buffer[256]
__attribute__((space(xmemory)));
int y_memory_buffer[256]
__attribute__((space(ymemory)));
int *xmemory;
int *ymemory;
int awb;
int xVal, yVal;
xmemory = x_memory_buffer;
ymemory = y_memory_buffer;
result = __builtin_clr(&xmemory, &xVal, 2,
&ymemory, &yVal, 2, &awb);
might generate:
clr A, [w8]+=2, w4, [w10]+=2, w5, w13
The compiler may need to spill w13 to ensure that it is available for the
write-back. It may be recommended to users that the register be
claimed for this purpose.
After this instruction:
• result will be cleared
• xVal will contain x_memory_buffer[0]
• yVal will contain y_memory_buffer[0]
• xmemory and ymemory will be incremented by 2, ready for the
next mac operation
Prototype: int __builtin_clr_prefetch(
int **xptr, int *xval, int xincr,
int **yptr, int *yval, int yincr, int *AWB);
DS51284G-page 144 © 2008 Microchip Technology Inc.