Power ISA™ Version 2.03 - Power.org

Version 2.03
3.3.10 Fixed-Point Trap Instructions
The Trap instructions are provided to test for a specified
set of conditions. If any of the conditions tested by
a Trap instruction are met, the system trap handler is
invoked. If none of the tested conditions are met,
instruction execution continues normally.
The contents of register RA are compared with either
the sign-extended value of the SI field or the contents
of register RB, depending on the Trap instruction. For
tdi and td, the entire contents of RA (and RB) participate
in the comparison; for twi and tw, only the contents
of the low-order 32 bits of RA (and RB) participate
in the comparison.
This comparison results in five conditions which are
ANDed with TO. If the result is not 0 the system trap
handler is invoked. These conditions are as follows.
TO Bit ANDed with Condition
0 Less Than, using signed comparison
1 Greater Than, using signed comparison
2 Equal
3 Less Than, using unsigned comparison
4 Greater Than, using unsigned comparison
Extended mnemonics for traps
A set of extended mnemonics is provided so that traps
can be coded with the condition as part of the mnemonic
rather than as a numeric operand. Some of
these are shown as examples with the Trap instructions.
See Appendix D for additional extended mnemonics.
Trap Word Immediate
D-form
Trap Word
X-form
twi
TO,RA,SI
tw
TO,RA,RB
3 TO RA SI
0 6 11 16 31
a EXTS((RA) 32:63 )
if (a < EXTS(SI)) & TO 0 then TRAP
if (a > EXTS(SI)) & TO 1 then TRAP
if (a = EXTS(SI)) & TO 2 then TRAP
if (a < u EXTS(SI)) & TO 3 then TRAP
if (a > u EXTS(SI)) & TO 4 then TRAP
The contents of RA 32:63 are compared with the
sign-extended value of the SI field. If any bit in the TO
field is set to 1 and its corresponding condition is met
by the result of the comparison, the system trap handler
is invoked.
If the trap conditions are met, this instruction is context
synchronizing (see Book III).
Special Registers Altered:
None
Extended Mnemonics:
Examples of extended mnemonics for Trap Word
Immediate:
Extended:
Equivalent to:
twgti Rx,value twi 8,Rx,value
twllei Rx,value twi 6,Rx,value
31 TO RA RB 4 /
0 6 11 16 21 31
a EXTS((RA) 32:63 )
b EXTS((RB) 32:63 )
if (a < b) & TO 0 then TRAP
if (a > b) & TO 1 then TRAP
if (a = b) & TO 2 then TRAP
if (a < u b) & TO 3 then TRAP
if (a > u b) & TO 4 then TRAP
The contents of RA 32:63 are compared with the contents
of RB 32:63 . If any bit in the TO field is set to 1 and
its corresponding condition is met by the result of the
comparison, the system trap handler is invoked.
If the trap conditions are met, this instruction is context
synchronizing (see Book III).
Special Registers Altered:
None
Extended Mnemonics:
Examples of extended mnemonics for Trap Word:
Extended:
Equivalent to:
tweq Rx,Ry tw 4,Rx,Ry
twlge Rx,Ry tw 5,Rx,Ry
trap tw 31,0,0
66
Power ISA -- Book I