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title "Processor type and stepping detection"
;++
;
; Copyright (c) 1989 Microsoft Corporation
;
; Module Name:
;
; cpu.asm
;
; Abstract:
;
; This module implements the assembley code necessary to determine
; cpu type and stepping information.
;
; Author:
;
; Shie-Lin Tzong (shielint) 28-Oct-1991.
; Some of the code is extracted from Cruiser (mainly,
; the code to determine 386 stepping.)
;
; Environment:
;
; 80x86 Real Mode.
;
; Revision History:
;
;
;--
.xlist
include cpu.inc
.list
;
; constant for i386 32-bit multiplication test
;
MULTIPLIER equ 00000081h
MULTIPLICAND equ 0417a000h
RESULT_HIGH equ 00000002h
RESULT_LOW equ 0fe7a000h
;
; Constants for Floating Point test
;
REALLONG_LOW equ 00000000
REALLONG_HIGH equ 3FE00000h
PSEUDO_DENORMAL_LOW equ 00000000h
PSEUDO_DENORMAL_MID equ 80000000h
PSEUDO_DENORMAL_HIGH equ 0000h
.386p
_TEXT SEGMENT PARA USE16 PUBLIC 'CODE'
ASSUME CS: _TEXT, DS:NOTHING, SS:NOTHING
;++
;
; USHORT
; HwGetProcessorType (
; VOID
; )
;
; Routine Description:
;
; This function determines type of processor (80486, 80386, 80286,
; and even 8086/8088). it relies on Intel-approved code that takes
; advantage of the documented behavior of the high nibble of the flag
; word in the REAL MODE of the various processors.
;
; For completeness, the code also checks for 8088/8086. But, it won't
; work.
;
; Arguments:
;
; None.
;
; Return Value:
;
; (ax) = x86h or 0 if unrecongnized processor.
;
;--
.8086
public _HwGetProcessorType
_HwGetProcessorType proc near
pushf ; save entry flags
;
; The MSB (bit 15) is always a one on the 8086 and 8088 and a zero on
; the 286, 386 and 486.
;
pushf
pop ax
and ax, NOT 08000h ; clear bit 15 of flags
push ax
popf ; try to put that in the flags
pushf
pop ax ; look at what really went into flags
test ax,08000h ; Was high bit set ?
jnz short x_86 ; if nz, still set, goto x_86
;
; Bit 14 (NT flag) and bits 13/12 (IOPL bit field) are always zero on
; the 286, but can be set on the 386 and 486.
;
or ax,07000h ; Try to set the NT/IOPL bits
push ax
popf ; Put in to the flags
sti ; (for VDMM/IOPL0)
pushf
pop ax ; look at actual flags
test ax,07000h ; Any high bits set ?
jz short x_286 ; if z, no, goto x_286
.386p
;
; The Alignment Check bit in flag can be set on 486 and is always zero
; on 386.
;
mov eax,cr0 ; test for 486 processor
push eax ; save CR0 value
and eax,not CR0_AM ; disable alignment check
mov cr0,eax
db ADDRESS_OVERRIDE
pushfd ; save original EFLAGS
db ADDRESS_OVERRIDE
pushfd ; try to set alignment check
or dword ptr [esp],EFLAGS_AC ; bit in EFLAGS
db ADDRESS_OVERRIDE
popfd
db ADDRESS_OVERRIDE
pushfd ; copy new flags into ECX
pop ecx ; [ecx] = new flags word
db ADDRESS_OVERRIDE
popfd ; restore original EFLAGS
pop eax ; restore original CR0 value
mov cr0,eax
and ecx, EFLAGS_AC ; did AC bit get set?
jz short x_386 ; if z, no, goto x_386
mov eax, 4h ; if nz, we have a 486 processor
.286p
jmp short hpt99
x_286:
mov ax, 2h ; Return 286 processor type.
jmp short hpt99
x_86:
mov ax, 0h ; Return 86h for 8088/8086 CPU type.
jmp short hpt99
x_386:
mov ax, 3h ; Return 386 processor type.
hpt99:
popf ; restore flags
ret
_HwGetProcessorType endp
.386p
;++
;
; USHORT
; HwGetCpuStepping (
; UHSORT CpuType
; )
;
; Routine Description:
;
; This function determines cpu stepping for the specified CPU type.
;
; Currently, this routine only determine stepping for 386 and 486.
;
; Arguments:
;
; CpuType - The Cpu type which its stepping information will be returned.
; The input value MUST be either 386 or 486.
;
; Return Value:
;
; [ax] - Cpu stepping. For example, [ax] = D0h for D0 stepping.
;
;--
HgcsCpuType equ [esp + 2]
public _HwGetCpuStepping
_HwGetCpuStepping proc
mov ax, HgcsCpuType ; [ax] = CpuType
cmp ax, 3h ; Is cpu = 386?
jz short Hgcs00 ; if z, yes, go Hgcs00
call Get486Stepping ; else, check for 486 stepping
jmp short Hgcs90 ; [ax] = Stepping information
Hgcs00:
call Get386Stepping ; [ax] = Stepping information
Hgcs90:
ret
_HwGetCpuStepping endp
;++
;
; USHORT
; Get386Stepping (
; VOID
; )
;
; Routine Description:
;
; This function determines cpu stepping for i386 CPU stepping.
;
; Arguments:
;
; None.
;
; Return Value:
;
; [ax] - Cpu stepping. For example, [ax] = D0h for D0 stepping.
; [ax] = 0 means bad CPU and stepping is not important.
;
;--
public Get386Stepping
Get386Stepping proc
call MultiplyTest ; Perform mutiplication test
jnc short G3s00 ; if nc, muttest is ok
mov ax, 0
ret
G3s00:
call Check386B0 ; Check for B0 stepping
jnc short G3s05 ; if nc, it's B1/later
mov ax, 0B0h ; It is B0/earlier stepping
ret
G3s05:
call Check386D1 ; Check for D1 stepping
jc short G3s10 ; if c, it is NOT D1
mov ax, 0D1h ; It is D1/later stepping
ret
G3s10:
mov ax, 0B1h ; assume it is B1 stepping
ret
Get386Stepping endp
;++
;
; USHORT
; Get486Stepping (
; VOID
; )
;
; Routine Description:
;
; This function determines cpu stepping for i486 CPU type.
;
; Arguments:
;
; None.
;
; Return Value:
;
; [ax] - Cpu stepping. For example, [ax] = D0h for D0 stepping.
;
;--
public Get486Stepping
Get486Stepping proc
call Check486AStepping ; Check for A stepping
jnc short G4s00 ; if nc, it is NOT A stepping
mov ax, 0A0h ; set to A stepping
ret
G4s00: call Check486BStepping ; Check for B stepping
jnc short G4s10 ; if nc, it is NOT a B stepping
mov ax, 0B0h ; set to B stepping
ret
;
; Before we test for 486 C/D step, we need to make sure NPX is present.
; Because the test uses FP instruction to do the detection.
;
G4s10: call _IsNpxPresent ; Check if cpu has coprocessor support?
cmp ax, 0
jz short G4s15 ; it is actually 486sx
call Check486CStepping ; Check for C stepping
jnc short G4s20 ; if nc, it is NOT a C stepping
G4s15:
mov ax, 0C0h ; set to C stepping
ret
G4s20: mov ax, 0D0h ; Set to D stepping
ret
Get486Stepping endp
;++
;
; BOOLEAN
; Check486AStepping (
; VOID
; )
;
; Routine Description:
;
; This routine checks for 486 A Stepping.
;
; It takes advantage of the fact that on the A-step of the i486
; processor, the ET bit in CR0 could be set or cleared by software,
; but was not used by the hardware. On B or C -step, ET bit in CR0
; is now hardwired to a "1" to force usage of the 386 math coprocessor
; protocol.
;
; Arguments:
;
; None.
;
; Return Value:
;
; Carry Flag clear if B or later stepping.
; Carry Flag set if A or earlier stepping.
;
;--
public Check486AStepping
Check486AStepping proc near
.386p
mov eax, cr0 ; reset ET bit in cr0
and eax, NOT CR0_ET
mov cr0, eax
mov eax, cr0 ; get cr0 back
test eax, CR0_ET ; if ET bit still set?
jnz short cas10 ; if nz, yes, still set, it's NOT A step
stc
ret
cas10: clc
ret
ret
Check486AStepping endp
;++
;
; BOOLEAN
; Check486BStepping (
; VOID
; )
;
; Routine Description:
;
; This routine checks for 486 B Stepping.
;
; On the i486 processor, the "mov to/from DR4/5" instructions were
; aliased to "mov to/from DR6/7" instructions. However, the i486
; B or earlier steps generate an Invalid opcode exception when DR4/5
; are used with "mov to/from special register" instruction.
;
; Arguments:
;
; None.
;
; Return Value:
;
; Carry Flag clear if C or later stepping.
; Carry Flag set if B stepping.
;
;--
public Check486BStepping
Check486BStepping proc
push ds
push bx
xor ax,ax
mov ds,ax ; (DS) = 0 (real mode IDT)
mov bx,6*4
push dword ptr [bx] ; save old int 6 vector
mov word ptr [bx].VectorOffset,offset Temporary486Int6
mov [bx].VectorSegment,cs ; set vector to new int 6 handler
c4bs50: db 0fh, 21h, 0e0h ; mov eax, DR4
nop
nop
nop
nop
nop
clc ; it is C step
jmp short c4bs70
c4bs60: stc ; it's B step
c4bs70: pop dword ptr [bx] ; restore old int 6 vector
pop bx
pop ds
ret
ret
Check486BStepping endp
;++
;
; BOOLEAN
; Temporary486Int6 (
; VOID
; )
;
; Routine Description:
;
; Temporary int 6 handler - assumes the cause of the exception was the
; attempted execution of an mov to/from DR4/5 instruction.
;
; Arguments:
;
; None.
;
; Return Value:
;
; none.
;
;--
Temporary486Int6 proc
mov word ptr [esp].IretIp,offset c4bs60 ; set IP to stc instruction
iret
Temporary486Int6 endp
;++
;
; BOOLEAN
; Check486CStepping (
; VOID
; )
;
; Routine Description:
;
; This routine checks for 486 C Stepping.
;
; This routine takes advantage of the fact that FSCALE produces
; wrong result with Denormal or Pseudo-denormal operand on 486
; C and earlier steps.
;
; If the value contained in ST(1), second location in the floating
; point stack, is between 1 and 11, and the value in ST, top of the
; floating point stack, is either a pseudo-denormal number or a
; denormal number with the underflow exception unmasked, the FSCALE
; instruction produces an incorrect result.
;
; Arguments:
;
; None.
;
; Return Value:
;
; Carry Flag clear if D or later stepping.
; Carry Flag set if C stepping.
;
;--
FpControl equ [ebp - 2]
RealLongSt1 equ [ebp - 10]
PseudoDenormal equ [ebp - 20]
FscaleResult equ [ebp - 30]
public Check486CStepping
Check486CStepping proc
push ebp
mov ebp, esp
sub esp, 30 ; Allocate space for temp real variables
;
; Initialize the local FP variables to predefined values.
; RealLongSt1 = 1.0 * (2 ** -1) = 0.5 in normalized double precision FP form
; PseudoDenormal = a unsupported format by IEEE.
; Sign bit = 0
; Exponent = 000000000000000B
; Significand = 100000...0B
; FscaleResult = The result of FSCALE instruction. Depending on 486 step,
; the value will be different:
; Under C and earlier steps, 486 returns the original value
; in ST as the result. The correct returned value should be
; original significand and an exponent of 0...01.
;
mov dword ptr RealLongSt1, REALLONG_LOW
mov dword ptr RealLongSt1 + 4, REALLONG_HIGH
mov dword ptr PseudoDenormal, PSEUDO_DENORMAL_LOW
mov dword ptr PseudoDenormal + 4, PSEUDO_DENORMAL_MID
mov word ptr PseudoDenormal + 8, PSEUDO_DENORMAL_HIGH
.387
fnstcw FpControl ; Get FP control word
fwait
or word ptr FpControl, 0FFh ; Mask all the FP exceptions
fldcw FpControl ; Set FP control
fld qword ptr RealLongSt1 ; 0 < ST(1) = RealLongSt1 < 1
fld tbyte ptr PseudoDenormal; Denormalized operand. Note, i486
; won't report denormal exception
; on 'FLD' instruction.
; ST(0) = Extended Denormalized operand
fscale ; try to trigger 486Cx errata
fstp tbyte ptr FscaleResult ; Store ST(0) in FscaleResult
cmp word ptr FscaleResult + 8, PSEUDO_DENORMAL_HIGH
; Is Exponent changed?
jz short c4ds00 ; if z, no, it is C step
clc
jmp short c4ds10
c4ds00: stc
c4ds10: mov esp, ebp
pop ebp
ret
Check486CStepping endp
;++
;
; BOOLEAN
; Check386B0 (
; VOID
; )
;
; Routine Description:
;
; This routine checks for 386 B0 or earlier stepping.
;
; It takes advantage of the fact that the bit INSERT and
; EXTRACT instructions that existed in B0 and earlier versions of the
; 386 were removed in the B1 stepping. When executed on the B1, INSERT
; and EXTRACT cause an int 6 (invalid opcode) exception. This routine
; can therefore discriminate between B1/later 386s and B0/earlier 386s.
; It is intended to be used in sequence with other checks to determine
; processor stepping by exercising specific bugs found in specific
; steppings of the 386.
;
; Arguments:
;
; None.
;
; Return Value:
;
; Carry Flag clear if B1 or later stepping
; Carry Flag set if B0 or prior
;
;--
ASSUME ds:nothing, es:nothing, fs:nothing, gs:nothing, ss:nothing
Check386B0 proc
push ds
push bx
xor ax,ax
mov ds,ax ; (DS) = 0 (real mode IDT)
mov bx,6*4
push dword ptr [bx] ; save old int 6 vector
mov word ptr [bx].VectorOffset,offset TemporaryInt6
mov [bx].VectorSegment,cs ; set vector to new int 6 handler
;
; Attempt execution of Extract Bit String instruction. Execution on
; B0 or earlier with length (CL) = 0 will return 0 into the destination
; (CX in this case). Execution on B1 or later will fail either due to
; taking the invalid opcode trap, or if the opcode is valid, we don't
; expect CX will be zeroed by any new instruction supported by newer
; steppings. The dummy int 6 handler will clears the Carry Flag and
; returns execution to the appropriate label. If the instruction
; actually executes, CX will *probably* remain unchanged in any new
; stepping that uses the opcode for something else. The nops are meant
; to handle newer steppings with an unknown instruction length.
;
xor ax,ax
mov dx,ax
mov cx,0ff00h ; Extract length (CL) == 0, (CX) != 0
b1c50: db 0fh, 0a6h, 0cah ; xbts cx,dx,ax,cl
nop
nop
nop
nop
nop
stc ; assume B0
jcxz short b1c70 ; jmp if B0
b1c60: clc
b1c70: pop dword ptr [bx] ; restore old int 6 vector
pop bx
pop ds
ret
Check386B0 endp
;++
;
; BOOLEAN
; TemporaryInt6 (
; VOID
; )
;
; Routine Description:
;
; Temporary int 6 handler - assumes the cause of the exception was the
; attempted execution of an XTBS instruction.
;
; Arguments:
;
; None.
;
; Return Value:
;
; none.
;
;--
TemporaryInt6 proc
mov word ptr [esp].IretIp,offset b1c60 ; set IP to clc instruction
iret
TemporaryInt6 endp
;++
;
; BOOLEAN
; Check386D1 (
; VOID
; )
;
; Routine Description:
;
; This routine checks for 386 D1 Stepping.
;
; It takes advantage of the fact that on pre-D1 386, if a REPeated
; MOVS instruction is executed when single-stepping is enabled,
; a single step trap is taken every TWO moves steps, but should
; occuu each move step.
;
; NOTE: This routine cannot distinguish between a D0 stepping and a D1
; stepping. If a need arises to make this distinction, this routine
; will need modification. D0 steppings will be recognized as D1.
;
; Arguments:
;
; None.
;
; Return Value:
;
; Carry Flag clear if D1 or later stepping
; Carry Flag set if B1 or prior
;
;--
assume ds:nothing, es:nothing, fs:nothing, gs:nothing, ss:nothing
Check386D1 proc
push ds
push bx
xor ax,ax
mov ds,ax ; (DS) = 0 (real mode IDT)
mov bx,1*4
push dword ptr [bx] ; save old int 1 vector
mov word ptr [bx].VectorOffset,offset TemporaryInt1
mov word ptr [bx].VectorSegment,cs ; set vector to new int 1 handler
;
; Attempt execution of rep movsb instruction with the Trace Flag set.
; Execution on B1 or earlier with length (CX) > 1 will trace over two
; iterations before accepting the trace trap. Execution on D1 or later
; will accept the trace trap after a single iteration. The dummy int 1
; handler will return execution to the instruction following the movsb
; instruction. Examination of (CX) will reveal the stepping.
;
sub sp,4 ; make room for target of movsb
xor si,si ; (ds:si) = 0:0
push ss ; (es:di) = ss:sp-4
pop es
mov di,sp
mov cx,2 ; 2 iterations
pushf
or word ptr [esp], EFLAGS_TF
popf ; cause a single step trap
rep movsb
d1c60: add sp,4 ; clean off stack
pop dword ptr [bx] ; restore old int 1 vector
stc ; assume B1
jcxz short d1cx ; jmp if <= B1
clc ; else clear carry to indicate >= D1
d1cx:
pop bx
pop ds
ret
Check386D1 endp
;++
;
; BOOLEAN
; TemporaryInt1 (
; VOID
; )
;
; Routine Description:
;
; Temporary int 1 handler - assumes the cause of the exception was
; trace trap at the above rep movs instruction.
;
; Arguments:
;
; (esp)->eip of trapped instruction
; cs of trapped instruction
; eflags of trapped instruction
;
;--
TemporaryInt1 proc
and word ptr [esp].IretFlags,not EFLAGS_TF ; clear caller's Trace Flag
mov word ptr [esp].IretIp,offset d1c60 ; set IP to next instruction
iret
TemporaryInt1 endp
;++
;
; BOOLEAN
; MultiplyTest (
; VOID
; )
;
; Routine Description:
;
; This routine checks the 386 32-bit multiply instruction.
; The reason for this check is because some of the i386 fail to
; perform this instruction.
;
; Arguments:
;
; None.
;
; Return Value:
;
; Carry Flag clear on success
; Carry Flag set on failure
;
;--
;
assume ds:nothing, es:nothing, fs:nothing, gs:nothing, ss:nothing
MultiplyTest proc
xor cx,cx ; 64K times is a nice round number
mlt00: push cx
call Multiply ; does this chip's multiply work?
pop cx
jc short mltx ; if c, No, exit
loop mlt00 ; if nc, YEs, loop to try again
clc
mltx:
ret
MultiplyTest endp
;++
;
; BOOLEAN
; Multiply (
; VOID
; )
;
; Routine Description:
;
; This routine performs 32-bit multiplication test which is known to
; fail on bad 386s.
;
; Note, the supplied pattern values must be used for consistent results.
;
; Arguments:
;
; None.
;
; Return Value:
;
; Carry Flag clear on success.
; Carry Flag set on failure.
;
;--
Multiply proc
mov ecx, MULTIPLIER
mov eax, MULTIPLICAND
mul ecx
cmp edx, RESULT_HIGH ; Q: high order answer OK ?
stc ; assume failure
jnz short mlpx ; N: exit with error
cmp eax, RESULT_LOW ; Q: low order answer OK ?
stc ; assume failure
jnz short mlpx ; N: exit with error
clc ; indicate success
mlpx:
ret
Multiply endp
;++
;
; BOOLEAN
; IsNpxPresent(
; VOID
; );
;
; Routine Description:
;
; This routine determines if there is any Numeric coprocessor
; present. If yes, the ET bit in CR0 will be set; otherwise
; it will be reset.
;
; Note that we do NOT determine its type (287, 387).
; This code is extracted from Intel book.
;
; Arguments:
;
; None.
;
; Return:
;
; TRUE - If NPX is present. Else a value of FALSE is returned.
;
;--
public _IsNpxPresent
_IsNpxPresent proc near
push bp ; Save caller's bp
.386p
mov eax, cr0
and eax, NOT CR0_ET ; Assume no NPX
mov edx, 0
.287
fninit ; Initialize NPX
mov cx, 5A5Ah ; Put non-zero value
push cx ; into the memory we are going to use
mov bp, sp
fnstsw word ptr [bp] ; Retrieve status - must use non-wait
cmp byte ptr [bp], 0 ; All bits cleared by fninit?
jne Inp10
or eax, CR0_ET
mov edx, 1
Inp10:
mov cr0, eax
pop ax ; clear scratch value
pop bp ; Restore caller's bp
mov eax, edx
ret
_IsNpxPresent endp
_TEXT ENDS
END
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