Motorola M68000 User Manual download pdf (Page 174)

Supervisor (Privileged) Instructions

MOTOROLA M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL 6-11

FRESTORE Restore Internal FRESTORE

Floating-Point State

(MC68881, MC68882, MC68040 only)

Operation: If in Supervisor State

Then FPU State Frame → Internal State

ELSE TRAP

Assembler

Syntax: FRESTORE < ea >

Attributes: Unsized

Description: Aborts the execution of any ﬂoating-point operation in progress and loads a

new ﬂoating-point unit internal state from the state frame located at the effective

address. The ﬁrst word at the speciﬁed address is the format word of the state frame.

It speciﬁes the size of the frame and the revision number of the ﬂoating-point unit that

created it. A format word is invalid if it does not recognize the size of the frame or the

revision number does not match the revision of the ﬂoating-point unit. If the format word

is invalid, FRESTORE aborts, and a format exception is generated. If the format word

is valid, the appropriate state frame is loaded, starting at the speciﬁed location and

proceeding through higher addresses.

The FRESTORE instruction does not normally affect the programmer’s model registers

of the floating-point coprocessor, except for the NULL state size, as described below.

It is only for restoring the user invisible portion of the machine. The FRESTORE

instruction is used with the FMOVEM instruction to perform a full context restoration of

the floating-point unit, including the floating- point data registers and system control

registers. To accomplish a complete restoration, the FMOVEM instructions are first

executed to load the programmer’s model, followed by the FRESTORE instruction to

load the internal state and continue any previously suspended operation.

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Motorola M68000 User Manual Page 174