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> Main > detect if cpu can enter pmiode |
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revolution 22 Jun 2010, 10:00
Read:
Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3A: System Programming Guide, Part 1 CHAPTER 18 ARCHITECTURE COMPATIBILITY |
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22 Jun 2010, 10:00 |
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ouadji 22 Jun 2010, 10:34
_________________ I am not young enough to know everything (Oscar Wilde)-  |
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22 Jun 2010, 10:34 |
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b1528932 22 Jun 2010, 11:24
no information about 0x66 prefix.
how do i know if i can use it? |
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22 Jun 2010, 11:24 |
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ouadji 22 Jun 2010, 11:38
Intel® 64 and IA-32 Architectures Optimization Reference Manual
3.4.2.3 Length-Changing Prefixes (LCP) The length of an instruction can be up to 15 bytes in length. Some prefixes can dynamically change the length of an instruction that the decoder must recognize. Typically, the pre-decode unit will estimate the length of an instruction in the byte stream assuming the absence of LCP. When the predecoder encounters an LCP in the fetch line, it must use a slower length decoding algorithm. With the slower length decoding algorithm, the predecoder decodes the fetch in 6 cycles, instead of the usual 1 cycle. Normal queuing throughout of the machine pipeline generally cannot hide LCP penalties. The prefixes that can dynamically change the length of a instruction include: • operand size prefix (0x66) • address size prefix (0x67) http://www.intel.com/Assets/PDF/manual/248966.pdf also : 2.1.2.2 Instruction Fetch Unit / Instruction PreDecode all processors based on x86 architecture are be able to do that. all cpu based on x86 architecture are be able to enter protected mode too ... (all cpu since 80286) _________________ I am not young enough to know everything (Oscar Wilde)- |
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22 Jun 2010, 11:38 |
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b1528932 22 Jun 2010, 21:22
Quote: all processors based on x86 architecture are be able to do that. so when i start executing my bootloader the first thing i should do is testing for cpuid in eflags.id? can i assume that i have access to upper 16 bits of eflags, and consequently being 32bit address aware? |
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22 Jun 2010, 21:22 |
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baldr 22 Jun 2010, 21:52
b1528932,
Probably you can safely assume 386+ CPU, or check and say "Upgrade your box, or press any key if you're brave enough." cpuid is Pentium+/later 486 feature. |
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22 Jun 2010, 21:52 |
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bitshifter 23 Jun 2010, 04:01
This was in the old Wofenstein3D sources
Code:
PROC _CheckIs386
PUBLIC _CheckIs386
pushf ; Save flag registers, we use them here
xor ax,ax ; Clear AX and...
push ax ; ...push it onto the stack
popf ; Pop 0 into flag registers (all bits to 0),
pushf ; attempting to set bits 12-15 of flags to 0's
pop ax ; Recover the save flags
and ax,08000h ; If bits 12-15 of flags are set to
cmp ax,08000h ; zero then it's 8088/86 or 80188/186
jz not386
mov ax,07000h ; Try to set flag bits 12-14 to 1's
push ax ; Push the test value onto the stack
popf ; Pop it into the flag register
pushf ; Push it back onto the stack
pop ax ; Pop it into AX for check
and ax,07000h ; if bits 12-14 are cleared then
jz not386 ; the chip is an 80286
mov ax,1 ; We now assume it's a 80386 or better
popf
retf
not386:
xor ax,ax
popf
retf
ENDP
Its in TASM IDEAL syntax! |
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23 Jun 2010, 04:01 |
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Tyler 11 Jul 2010, 01:06
HelpPC, Misc -> CPU topic wrote:
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11 Jul 2010, 01:06 |
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