7-10
FLOATING-POINT UNIT
increment TOP by one. (For the FPU, a load operation is equivalent to a push and a store oper-
ation is equivalent to a pop.)
If a load operation is performed when TOP is at 0, register wraparound occurs and the new value
of TOP is set to 7. The floating-point stack-overflow exception indicates when wraparound
might cause an unsaved value to be overwritten (refer to Section 7.8.1.1., Stack Overflow or
Underflow Exception (#IS)).
Figure 7-5. FPU Execution Environment
Figure 7-6. FPU Data Register Stack
0
79
R7
R6
R5
R4
R3
R2
R1
R0
FPU Data Registers
Exponent
Significand
786463
15
Control
Register
0
Status
Register
Tag
Register
0
47
FPU Instruction Pointer
FPU Operand (Data) Pointer
10
Opcode
0
Sign
7
6
5
4
3
2
1
0
FPU Data Register Stack
ST(2)
ST(1)
ST(0)
Top
011B
Growth
Stack
