UefiCpuPkg/Library/BaseUefiCpuLib/X64/InitializeFpu.asm

   1 ;------------------------------------------------------------------------------
   2 ;*
   3 ;*   Copyright (c) 2009 - 2012, Intel Corporation. All rights reserved.<BR>
   4 ;*   This program and the accompanying materials
   5 ;*   are licensed and made available under the terms and conditions of the BSD License
   6 ;*   which accompanies this distribution.  The full text of the license may be found at
   7 ;*   http://opensource.org/licenses/bsd-license.php
   8 ;*
   9 ;*   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 ;*   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11 ;*
  12 ;*
  13 ;------------------------------------------------------------------------------
  14
  15
  16 .const
  17 ;
  18 ; Float control word initial value:
  19 ; all exceptions masked, double-extended-precision, round-to-nearest
  20 ;
  21 mFpuControlWord       DW      037Fh
  22 ;
  23 ; Multimedia-extensions control word:
  24 ; all exceptions masked, round-to-nearest, flush to zero for masked underflow
  25 ;
  26 mMmxControlWord       DD      01F80h
  27
  28 .code
  29
  30
  31 ;
  32 ; Initializes floating point units for requirement of UEFI specification.
  33 ;
  34 ; This function initializes floating-point control word to 0x027F (all exceptions
  35 ; masked,double-precision, round-to-nearest) and multimedia-extensions control word
  36 ; (if supported) to 0x1F80 (all exceptions masked, round-to-nearest, flush to zero
  37 ; for masked underflow).
  38 ;
  39 InitializeFloatingPointUnits PROC PUBLIC
  40
  41     ;
  42     ; Initialize floating point units
  43     ;
  44     ; The following opcodes stand for instruction 'finit'
  45     ; to be supported by some 64-bit assemblers
  46     ;
  47     DB      9Bh, 0DBh, 0E3h
  48     fldcw   mFpuControlWord
  49
  50     ;
  51     ; Set OSFXSR bit 9 in CR4
  52     ;
  53     mov     rax, cr4
  54     or      rax, BIT9
  55     mov     cr4, rax
  56
  57     ldmxcsr mMmxControlWord
  58
  59     ret
  60 InitializeFloatingPointUnits ENDP
  61
  62 END