Intel 80287, 80286 manual Advanced Topics, Example of NPX Context Switching

intel" ADVANCED TOPICS

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154, SEGIHHT CDHTAIHS PRIVILEGED INSTRUCTIOHS

55ud

Set new tuk ld ud glt old Go to TSS 11111

"Address TSS of previoul HPI tllk Sive old NPI S\I\I

I Get current NPX state

I Retllrn to Interrupted program

Figure 11-3. Example of NPX Context Switching

When a program changes a descriptor that is shared with other processors, it should broadcast this fact to the other processors. This broadcasting can be done with .an inter-processor inierrupl. Tht; hiii,;11;;, for this interrupt must ensure that the segment registers, the LDTR and the TR, are re-Ioaded. This happens automatically if the interrupt is serviced by a.task switch.

Modification of descriptors of shared segments in multi-processor systems may require that the on-chip descriptors also be updated. For example, one processor may attempt to mark the descriptor of a shared segment as not-present while another is using it. Software has to ensure that the descriptors in the segment register caches are updated with the new information. The segment register caches can be

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