User's Manual

PROGRAMMING NUMERIC APPLICATIONS
FRSTOR
source
FRSTOR (restore state) reloads the 80287 from the 94-byte memory area defined by the source operand.
This information should have been written by a previous
FSA VEjFNSA VE instruction and not altered
by any other instruction. An FW AIT
is not required after FRSTOR. FRSTOR will automatically wait
and check for interrupts until all data transfers are completed before continuing to the next instruction.
Note that the
80287 "reacts" to its new state at the conclusion of the FRSTOR; it will, for example,
generate an exception request if the exception and mask bits
in the memory image so indicate when
the next WAIT or error-checking-ESC instruction
is executed.
FSTENV IFNSTENV destination
FSTENV jFNSTENV (store environment) writes the 80287's basic status-control, status, and tag
words, and exception
pointers-to the memory location defined by the destination operand. Typically,
the environment
is saved on the CPU stack. FSTENV jFNSTENV is often used by exception handlers
because it provides access
to the exception pointers that identify the offending instruction and operand.
After saving the environment,
FSTENV /FNSTENV sets all exception masks in the processor. FSTENV
checks for pending errors before executing, FNSTENV does not.
Figure
2-2 shows the format of the environment data in memory. FNSTENV does not store the
environment until all
NPX activity has completed. Thus, the data saved by the instruction reflects the
80287 after any previously decoded instruction has been executed. After writing the environment image
to memory, FNSTENV
jFSTENV initializes the 80287 state as if FNINIT jFINIT had been executed.
15
CONTROL WORD
STATUS WORD
TAG WORD
INSTRUCTION POINTER (15-0)
INSTRUCTION
1)1 I
INSTRUCTION
POINTER
(19-16) 0
OPCODE (10-0)
DATA POINTER (15-0)
DATA POINTER I
(19-16)
0
15 1211
REAL MODE
MEMORY
OFFSET
+0
+2
+4
+6
+6
+10
+12
15
CONTROL WORD
STATUS WORD
TAG WORD
IPOFFSET
CSSELECTOR
DATA OPERAND OFFSET
DATA OPERAND SELECTOR
PROTECTED MODE
Figure 2-2. FSTENV IFLDENV Memory Layout
2-19
MEMORY OFFSET
+0
+2
+4
+6
+8
+10
+12
G30108