Re: [rtl] MMX in RT-tasks

[smithk@biotronik.com (Kirk Smith)]

> Date:          Sun, 04 Jul 1999 11:04:07 +0200
> From:          Erwin Rol <erwin@muffin.org>
> To:            RT-Linux <rtl@rtlinux.cs.nmt.edu>
> Subject:       [rtl] MMX in RT-tasks

> Is it possible to just mark a RT-task and than use MMX instructions in 
> it. I will not be using floating point, just MMX (i need to make a
> large number of addtions). Are there any special things to take care of

I beleive (in Pentium MMXes atleast), the MMX instruction set uses the same 
registers as the floating point operations.  So using MMX instructions would 
overwrite stuff stored in floating point registers for other processes.  Thus, 
you would need to save MMX state inside the process like any other CPU 
register.  I assume this is done by the OS however for Kernal / User switching, 
it probably isn't done between RTL apps and the kernal.
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