7
"++++++]+++++++'It F+L,
MC88881/MC68882
¢,. __,.,e =----3
(A SIMILAR SEQUENCE tS FOLL0~0 OURING THE PcFTIAL PHASE 0F AP~ FSAVE I~STFIUCT10N.
AS IND]CA]ED IN THE FSAVE PROTQCOL DIAGRAM)
Figure 7-36. Mid-Instruction Interrupt Dialog
response CIR encoding to the null primitive, the interrupt handler (or any other routine)
must not casually read the response CIR to determine the status of the FPCP, or the
suspended protocol is disrupted. Rather, the only valid method for checking the status of
the FPCP is to execute the FSAVE instruction and examine the state frame that is generated;
followed by an FRESTORE instruction to reinstate the previous context of the FPCP.
7.5.4.4 TAKE BSUN EXCEPTION. This dialog is utilized by the FPCP when a conditional
instruction is initiated by writing one of the IEEE nonaware conditional predicates to the
condition CIR with the SNAN enable bit and the NAN condition code bit set. The dialog is
shown in Figure 7-37.
MC68020,MC°,030 I t --I I J
w
Figure 7-37. Take BSUN Exception Dialog
FREESCALE
7-38
MC68881/MC68882 USER'S MANUAL
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