NEC uPD98502 User Manual page 499

JALR
31 26 25
SPECIAL
0 0 0 0 0 0
6
Format:
JALR rs
JALR rd, rs
Description:
The program unconditionally jumps to the address contained in general register rs , with a delay of one instruction.
When a MIPS16 instruction can be executed, the program unconditionally jumps with a delay of one instruction to
the address indicated by the value of clearing the least significant bit of the general-purpose register rs to 0. Then,
the content of the least significant bit of the general-purpose register rs is set to the ISA mode bit (internal). The
address of the instruction after the delay slot is placed in general register rd . The default value of rd , if omitted in
the assembly language instruction, is 31. When a MIPS16 instruction can be executed, the value of bit 0 of rd
indicates the ISA mode bit before jump. Register specifiers rs and rd may not be equal, because such an
instruction does not have the same effect when re-executed. Because storing a link address destroys the contents
of rs if they are equal. However, an attempt to execute this instruction is not trapped, and the result of executing
such an instruction is undefined.
Since 32-bit length instructions must be word-aligned, a JALR instruction must specify a target register ( rs ) that
contains an address whose two low-order bits are zero when a MIPS16 instruction can be executed. If these low-
order bits are not zero, an address error exception will occur when the jump target instruction is subsequently
fetched.
Operation:
temp ← GPR [rs]
32, 64 T:
If MIPS16EN = 1 then
GPR [rd] ← (PC + 8)
else
GPR [rd] ← PC + 8
endif
T+1: If MIPS16EN = 1 then
PC ← temp
ISA MODE ← temp
else
PC ← temp
endif
Exceptions:
None
APPENDIX A MIPS III INSTRUCTION SET DETAILS
Jump And Link Register
21 20 16 15
0
rs
0 0 0 0 0
5 5
|| ISA MODE
63..1
|| 0
63..1
0
Preliminary User's Manual S15543EJ1V0UM
11 10 6 5
0
rd
0 0 0 0 0
5 5
JALR
0
JALR
0 0 1 0 0 1
6
499