Fujitsu CM71-00101-5E Manuale Utente

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CHAPTER 4  RESET AND "EIT" PROCESSING

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When a coprocessor is used in a multi-tasking environment, the internal resources of the coprocessor

become part of the system context. Thus whenever context switching occurs, it is necessary to save or

restore the contents of the coprocessor. Problems arise when there are hidden coprocessor errors remaining

from former tasks at the time of context switching.

In such cases, when the exception is detected in a coprocessor context save instruction by the dispatcher, it

becomes impossible to return the information to the former task. This problem is avoided by executing a

"COPSV" instruction, which does not send notification of coprocessor errors but acts to clear the internal

error. Note that the error information is retained in the status information that is saved. If the saved status

information is returned to the coprocessor at the time of re-dispatching to the former task, the hidden error

condition is cleared and the CPU is notified when the next coprocessor instruction is executed.

Figure 4.5-1 shows an example in which notification to the coprocessor does not succeed, and Figure 4.5-2

illustrates the use of the "COPSV" instruction to save and restore error information.  

Coprocessor

CPU(main)

CPU(dispatcher)

Hidden error condition

Notification

Interrupt

COPST

COPOP

Coprocessor

CPU
(main)

CPU(dispatcher)

Hidden error condition

Hidden error condition

No notification

Interrupt

COPSV

COPLD

COPOP

RETI

COPST