Identifying CPU - Revision history

Kindman: Added CPU reset

2012-08-15T11:58:05Z

Added CPU reset

← Older revision		Revision as of 13:58, 15 August 2012
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	* Check the presence of the [[#CPUID instruction\|CPUID instruction]].		* Check the presence of the [[#CPUID instruction\|CPUID instruction]].
	** If CPUID is supported, use the instruction to get CPU information and supported instructions.		** If CPUID is supported, use the instruction to get CPU information and supported instructions.
	** If CPUID is not supported, reset the CPU to get its signature.		** If CPUID is not supported, [[#Resetting the CPU to get its signature\|reset the CPU to get its signature]].
	* Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.		* Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.


	In AMC-OS, CPU identification is done during AMC-OS Loader execution. Code is found in <code>CORE\SRC\~~AMCOSLDR~~\CPUID16.ASM</code>.		In AMC-OS, CPU identification is done during AMC-OS Loader execution. Code is found in <code>CORE\SRC\CODE16\CPUID16.ASM</code>.

	Intel describes the complete process of CPU identification in [http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/processor-identification-cpuid-instruction-note.pdf Application Note 485].		Intel describes the complete process of CPU identification in [http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/processor-identification-cpuid-instruction-note.pdf Application Note 485].
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	* [http://support.amd.com/us/Embedded_TechDocs/25481.pdf AMD Specific CPUID specification].		* [http://support.amd.com/us/Embedded_TechDocs/25481.pdf AMD Specific CPUID specification].
	* [http://www.sandpile.org/ Sandpile website] provides a complete list of expectable CPUID results with other manufacturers (Cyrix, IDT, NexGen...).		* [http://www.sandpile.org/ Sandpile website] provides a complete list of expectable CPUID results with other manufacturers (Cyrix, IDT, NexGen...).

			===Resetting the CPU to get its signature===

			When CPU starts, the CPU signature is placed in the EDX register. Our goal is to intercept execution the soonest possible, hoping that EDX value has not been trashed.

			After a reset, the BIOS normally examines the ''shutdown byte'' in CMOS to know what happened and act accordingly. A shutdown value of 0A returns control to FAR location stored at the offset 0067 of BIOS data segment -- so basically JMP FAR [0040:0067]. In some cases, the control is not given back to the CMOS and an INT 06H (invalid instruction) is triggered. What we have to do is intercept control in both cases, storing EDX, and restore system normal condition :
			* Disable all interrupts, and mask all of them in PIC
			* Set return value in 0040:0067 and INT06 handler
			* Disable NMI, save all registers and shutdown byte
			* Set shutdown byte 0A and reset
			* Save EDX
			* Set shutdown byte 05 (same as before, but reinitializes hardware correctly) and reset
			* Enable NMI, restore all registers, PIC unmasking and interrupts

			In the EDX value saved, you can have the signature either :
			* in DX where it should be
			* in the upper part of EDX where BIOS saved it for us
			* nowhere if it was trashed by BIOS

Kindman at 11:34, 15 August 2012

2012-08-15T11:34:05Z

← Older revision		Revision as of 13:34, 15 August 2012
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	==Introduction==		==Introduction==

	All x86 CPUs starting with the 80386 have a signature indicating their type, family, model and stepping.		All x86 CPUs starting with the 80386 have a signature indicating their type, family, model and stepping. This signature is placed in EDX register when CPU starts. Starting with some late 486SX, a CPUID instruction has been added to retrieve easily this signature along with other CPU information. When the instruction is not supported, it is necessary to shutdown the CPU and get back control as soon as possible to store the value.

	This signature is placed in EDX register when CPU starts. Starting with some late 486SX, a CPUID instruction has been added to retrieve easily this signature along with other CPU information. When the instruction is not supported, it is necessary to shutdown the CPU and get back control as soon as possible to store the value.

	In AMC-OS, CPU identification is done during [[AMC-OS Loader]] execution.		In AMC-OS, CPU identification is done during [[AMC-OS Loader]] execution.
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	Identifying an Intel-compatible x86 CPU is done in several steps :		Identifying an Intel-compatible x86 CPU is done in several steps :
	* Check that we have a 32-bits 80386 minimum CPU.		* Check that we have a 32-bits 80386 minimum CPU.
	* Check the presence of the CPUID instruction.		* Check the presence of the [[#CPUID instruction\|CPUID instruction]].
	** If CPUID is supported, use the instruction to get CPU information and supported instructions.		** If CPUID is supported, use the instruction to get CPU information and supported instructions.
	** If CPUID is not supported, reset the CPU to get its signature.		** If CPUID is not supported, reset the CPU to get its signature.
	* Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.		* Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.


	In AMC-OS, CPU identification is done during AMC-OS Loader execution. Code is found in <code>CORE\SRC\AMCOSLDR\CPUID16.ASM</code>.		In AMC-OS, CPU identification is done during AMC-OS Loader execution. Code is found in <code>CORE\SRC\AMCOSLDR\CPUID16.ASM</code>.
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	Follow this procedure to determine if we have at least a 386 CPU :		Follow this procedure to determine if we have at least a 386 CPU :
	* On a 8086/8088, bits 12-15 are always set to 1.		* On a 8086/8088, bits 12-15 of FLAGS register are always set to 1. Test setting them to 0.
	** Put all bits of FLAGS register to 0 ~~using POPF.~~		* On a 80286, bits 12-14 of FLAGS register are always set to 0. Test setting them to 1.
	** If bits 12-15 are still set after, we have a 8086/8088.
	* On a 80286, bits 12-14 are always set to 0.
	** Set bits 12-14 of EFLAGS (0x7000) using POPF.
	** If bits 12-14 are unset after, we have a 80286, a 386+ else.

	You can also check the presence of a 486 by toggling bit 18 of EFLAGS register. It won't work on a 386.		You can also check the presence of a 486 by toggling bit 18 of EFLAGS register. It won't work on a 386.

Kindman at 11:30, 15 August 2012

2012-08-15T11:30:38Z

@@ Line 1: / Line 1: @@
 ==Introduction==
 Identifying an Intel-compatible x86 CPU is done in several steps :
@@ Line 8: / Line 16: @@
 * Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.
-==External documentation==
+In AMC-OS, CPU identification is done during AMC-OS Loader execution. Code is found in <code>CORE\SRC\AMCOSLDR\CPUID16.ASM</code>.
 Intel describes the complete process of CPU identification in [http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/processor-identification-cpuid-instruction-note.pdf Application Note 485].
-AMD describes their specific CPUID implementation [http://support.amd.com/us/Embedded_TechDocs/25481.pdf here]
+===Checking 80386 CPU===

Kindman at 22:02, 14 August 2012

2012-08-14T22:02:55Z

← Older revision		Revision as of 00:02, 15 August 2012
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	* Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.		* Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.

	==~~Additional information~~==		==External documentation==

	Intel describes the complete process of CPU identification in [http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/processor-identification-cpuid-instruction-note.pdf Application Note 485].		Intel describes the complete process of CPU identification in [http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/processor-identification-cpuid-instruction-note.pdf Application Note 485].

	AMD describes their specific CPUID implementation [http://support.amd.com/us/Embedded_TechDocs/25481.pdf here]		AMD describes their specific CPUID implementation [http://support.amd.com/us/Embedded_TechDocs/25481.pdf here]

Kindman at 22:02, 14 August 2012

2012-08-14T22:02:20Z

← Older revision		Revision as of 00:02, 15 August 2012
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	==Additional information==		==Additional information==

	Intel describes the complete process of CPU identification in [http://www.intel.com/content/www/us/en/~~processors~~/processor-identification-cpuid-instruction-note.~~html~~ Application Note 485].		Intel describes the complete process of CPU identification in [http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/processor-identification-cpuid-instruction-note.pdf Application Note 485].

	AMD describes their specific CPUID implementation [http://support.amd.com/us/Embedded_TechDocs/25481.pdf here]		AMD describes their specific CPUID implementation [http://support.amd.com/us/Embedded_TechDocs/25481.pdf here]

Kindman at 22:01, 14 August 2012

2012-08-14T22:01:49Z

← Older revision		Revision as of 00:01, 15 August 2012
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	Intel describes the complete process of CPU identification in [http://www.intel.com/content/www/us/en/processors/processor-identification-cpuid-instruction-note.html Application Note 485].		Intel describes the complete process of CPU identification in [http://www.intel.com/content/www/us/en/processors/processor-identification-cpuid-instruction-note.html Application Note 485].

			AMD describes their specific CPUID implementation [http://support.amd.com/us/Embedded_TechDocs/25481.pdf here]

Kindman: Created page with "==Introduction== Identifying an Intel-compatible x86 CPU is done in several steps : * Check that we have a 32-bits 80386 minimum CPU. * Check the presence of the CPUID instru..."

2012-08-14T21:57:44Z

Created page with "==Introduction== Identifying an Intel-compatible x86 CPU is done in several steps : * Check that we have a 32-bits 80386 minimum CPU. * Check the presence of the CPUID instru..."

New page

==Introduction==

Identifying an Intel-compatible x86 CPU is done in several steps :
* Check that we have a 32-bits 80386 minimum CPU.
* Check the presence of the CPUID instruction.
** If CPUID is supported, use the instruction to get CPU information and supported instructions.
** If CPUID is not supported, reset the CPU to get its signature.
* Calculate the operating frequency of the CPU by timing the execution of a sequence of instructions.

==Additional information==

Intel describes the complete process of CPU identification in [http://www.intel.com/content/www/us/en/processors/processor-identification-cpuid-instruction-note.html Application Note 485].