Using VFP instructions

You must use the following gcc and binutils versions to allow the compiler and assembler to use VFP instructions:

• gcc 4.2 or later
• binutils 2.18 or later

The following compiler flags are required:

-mfpu=vfp -mfloat-abi=softfp

This causes gcc to use VFP instructions for floating point, and to use the soft-float ABI (application binary interface) to pass floating-point arguments and results in ARM registers. The ABI defines the calling convention of register usage for arguments and results in procedure calls.

Application code must not change FPSCR bits that would change the mode to anything other than the RunFast operation:

• The default NaN mode (bit 25) must be set to 1.
• The bit (bit 24) that denotes Flush-to-zero mode must be set to 1.
• The rounding mode (bit 23:22) must be set to 00 to enable the Round-to-nearest mode.

If these bits are altered, it's possible for the VFP to generate exceptions that require software support. Since no software support is currently provided, this will result in a SIGFPE signal.