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Index > OS Construction > Am I forced to use 8086's instructions in real mode?

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emc



Joined: 20 Aug 2011
Posts: 90
Location: France
emc
Hello,

I would want know if I am forced to use only the 8086's instructions in real mode, because I am trying to write a little kernel (real mode) that checks if the CPU has the SSE4 set, using CPUID (that is not in the 8086 set) instruction.

Regards.

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Post 26 Aug 2011, 16:10
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DJ Mauretto



Joined: 14 Mar 2007
Posts: 464
Location: Rome,Italy
DJ Mauretto
Quote:
I would want know if I am forced to use only the 8086's instructions in real mode


NO Very Happy

Today 8086 cpu is rare, anyway you can write code that checks the processor type..

* FROM INTEL *

Check for 8086:
Bits 12-15 of the FLAGS register are always set on the 8086 processor

Check for 286:
Bits 12-15 of the FLAGS register are always clear on the
286 processor in real-address mode.

Check for 386 processor:
The AC bit, bit #18, is a new bit introduced in the EFLAGS
register on the Intel486 processor to generate alignment faults.
This bit cannot be set on the Intel386 processor.


Check for 486 processor:
Checking for ability to set/clear ID flag (Bit 21) in EFLAGS
which indicates the presence of a processor with the CPUID instruction.

Have Fun
Wink

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Post 26 Aug 2011, 17:16
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emc



Joined: 20 Aug 2011
Posts: 90
Location: France
emc
Ok, thanks for these informations DJ Mauretto Very Happy
Post 26 Aug 2011, 17:23
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