IntelFsp2Pkg/FspSecCore/Ia32/InitializeFpu.nasm

;------------------------------------------------------------------------------
;
; Copyright (c) 2015, Intel Corporation. All rights reserved.<BR>
; This program and the accompanying materials
; are licensed and made available under the terms and conditions of the BSD License
; which accompanies this distribution.  The full text of the license may be found at
; http://opensource.org/licenses/bsd-license.php.
;
; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
;
; Abstract:
;
;------------------------------------------------------------------------------


SECTION .data
;
; Float control word initial value:
; all exceptions masked, double-precision, round-to-nearest
;
ASM_PFX(mFpuControlWord):
    dw    0x027F
;
; Multimedia-extensions control word:
; all exceptions masked, round-to-nearest, flush to zero for masked underflow
;
ASM_PFX(mMmxControlWord):
     dd     0x01F80

SECTION .text

;
; Initializes floating point units for requirement of UEFI specification.
;
; This function initializes floating-point control word to 0x027F (all exceptions
; masked,double-precision, round-to-nearest) and multimedia-extensions control word
; (if supported) to 0x1F80 (all exceptions masked, round-to-nearest, flush to zero
; for masked underflow).
;

global ASM_PFX(InitializeFloatingPointUnits)
ASM_PFX(InitializeFloatingPointUnits):


    push    ebx

    ;
    ; Initialize floating point units
    ;
    finit
    fldcw    [ASM_PFX(mFpuControlWord)]

    ;
    ; Use CpuId instructuion (CPUID.01H:EDX.SSE[bit 25] = 1) to test
    ; whether the processor supports SSE instruction.
    ;
    mov     eax, 1
    cpuid
    bt      edx, 25
    jnc     Done

    ;
    ; Set OSFXSR bit 9 in CR4
    ;
    mov     eax, cr4
    or      eax, BIT9
    mov     cr4, eax

    ;
    ; The processor should support SSE instruction and we can use
    ; ldmxcsr instruction
    ;
    ldmxcsr [ASM_PFX(mMmxControlWord)]
Done:
    pop     ebx

    ret