
Sun Microelectronics
246
UltraSPARC User’s Manual
RD:
IEEE Std 754-1985 Rounding Direction.
TEM:
5-bit trap enable mask for the IEEE-754 floating-point exceptions. If a
floating-point operate instruction produces one or more exceptions, the
corresponding cexc/aexc bits are set and an
fp_exception_ieee_754
(with
FSR.ftt=1,
IEEE_754_exception
) exception is generated.
NS:
When this field = 0, UltraSPARC produces IEEE-754 compatible results.
In particular, subnormal operands or results may cause a trap. When this
field=1, UltraSPARC may deliver a non-IEEE-754 compatible result. In
particular, subnormal operands and results may be flushed to zero. See
Table 14-4, “Subnormal Operand Trapping Cases (NS=0),” on page 243
and Table 14-5, “Subnormal Result Trapping Cases (NS=0),” on page 243.
ver:
This field identifies a particular implementation of the UltraSPARC FPU
architecture.
ftt:
The 3-bit floating point trap type field is set whenever an floating-point
instruction causes the
fp_exception_ieee_754
or
fp_exception_other
traps.
Note:
UltraSPARC neither detects nor generates the following trap types
directly in hardware:
hardware_error
,
invalid_fp_register
.
Table 14-8
Floating-Point Rounding Modes
RD
Round Toward
0
Nearest (even if tie)
1
0
2
+
∞
3
–
∞
Table 14-9
Floating-Point Trap Type Values
ftt
Floating-Point Trap Type
Trap Signalled
0
None
—
1
IEEE_754_exception
fp_exception_ieee_754
2
unfinished_FPop
fp_exception_other
3
unimplemented_FPop
fp_exception_other
4
sequence_error
fp_exception_other
5
hardware_error
—
6
invalid_fp_register
—
7
reserved
—
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