AMD-K6 Datasheet, PDF (45/346 Pages) Advanced Micro Devices – AMD-K6 Processor

20695H/0—March 1998
Preliminary Information
AMD-K6^® Processor Data Sheet
The FPU control word register allows a programmer to manage
the FPU processing options. Figure 12 shows the format of this
register.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
YR
P
CC
PUOZ D I
MMMM MM
Reserved
Symbol
Y
RC
PC
PM
UM
OM
ZM
DM
IM
Description
Bits
Infinity Bit (80287 compatibility) 12
Rounding Control
11–10
Precision Control
9–8
Exception Masks
Precision
5
Underflow
4
Overflow
3
Zero Divide
2
Denormalized Operation
1
Invalid Operation
0
Rounding Control Information
00b = Round to the nearest or even number
01b = Round down toward negative infinity
10b = Round up toward positive infinity
11b = Truncate toward zero
Precision Control Information
00b = 24 bits Single Precision Real
01b = Reserved
10b = 53 bits Double Precision Real
11b = 64 bits Extended Precision Real
Figure 12. FPU Control Word Register
The FPU tag word register contains information about the
registers in the register stack. Figure 13 shows the format of this
register.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
TAG TAG TAG TAG TAG TAG TAG TAG
(FPR7 (FPR6 (FPR5 (FPR4 (FPR3 (FPR2 (FPR1 (FPR0
Figure 13. FPU Tag Word Register
Tag Values
00 = Valid
01 = Zero
10 = Special
11 = Empty
Chapter 3
Software Environment
27