4.2.5.1 General-Purpose Register Operands

PIC32M Registers

Register operands can be specified using the appropriate register number preceded by a dollar sign ($).The following example shows assembly source code using register number operands.

.text
# Add Word
  li     $2, 123
  li     $3, 456
  add    $4, $2, $3

If you use the compilation driver (xc32-gcc) to preprocess the source code with the CPP-style preprocessor before assembling, you can take advantage of macros that are provided in the <xc.h> header file. These macros map conventional register names to the corresponding register number. The following example shows assembly source code using conventional register names for operands. See the MPLAB® XC32 C/C++ Compiler User’s Guide for PIC32/SAM MCUs for additional information on PIC32M register conventions and the compiler's runtime environment.

#include <xc.h>
.text
/* Add Word */
  li    v0, 123      /* v0 is a return-value register */
  li    v1, 456      /* v1 is a return-value register */
  add   a0, v0, v1   /* a0 is an argument register */

Note that these macro names cannot ordinarily be used within assembly code placed inline with C code using the __asm() statement.

PIC32C/SAM Registers

  ldr    r2, [r7, #4]
  ldr    r3, [r7]
  add    r3, r3, r2