lv1_set_vmx_graphics_mode (97)

Set the Single Precision mode of the vmx graphics units in the PPU

result = lv1_set_vmx_graphics_mode( mode );

Notes:

This is a call to set the single precision rounding mode of the VMX units in the Cell PPUs. The AltiVec/VMX SIMD/Vector processing unit has 2 rounding modes for dealing with Single-precision floating-point. IEEE 754-1985 and SPE-compatible SIMD graphics-rounding mode.

The Cell Broadband Engine Programming Handbook has this to say on the subject: The first implementation of the Cell Broadband Engine Architecture (CBEA) (the CBE processor) supports instructions with a graphics rounding mode. This mode allows programs written with vector/SIMD multimedia extension instructions to produce floating-point results that are equivalent in precision to those written in the SPU instruction set. In this mode, as in the SPU environment, the default rounding mode is round to zero, denormals are treated as zero, and there are no infinities or NaNs.

To change this mode, bit 12 in the HID1 register (known as grap_md or grap_mode in various documents). HID1 is a HV privileged resource, hence to change the mode from Supervisor mode requires a HV call.

Reference Documents: Cell Broadband Engine Programming Handbook V1.1 Cell Broadband Engine Registers V1.5

Tests:

Info taken from kboot-10\dl\linux-2.6.16\include\asm-powerpc\lv1calltab.h (kboot-20061208)

When recompiled into Kernel module init function, accepts values of 0 and 1 for p1. All other values return -17 (LV1_ILLEGAL_PARAMETER_VALUE)