twi
Trap Word Immediate - 0C 00 00 00
twi
Instruction Syntax
| Mnemonic | Format | Flags |
| twi | TO,rA,SIMM | None |
Instruction Encoding
0
0
1
1
0
0
T
T
T
T
T
A
A
A
A
A
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
| Field | Bits | Description |
| Primary Opcode | 0-5 | 001100 (0x0C) |
| TO | 6-10 | Trap condition |
| rA | 11-15 | Source register |
| SIMM | 16-31 | Signed immediate value |
Operation
If condition specified by TO is met, then trap
The twi instruction compares the value in register rA with the signed immediate value according to the condition specified by TO. If the condition is met, a program interrupt is generated.
Note: The twi instruction is used for conditional trapping based on register-to-immediate comparisons. Common trap conditions include equal, less than, greater than, etc.
Affected Registers
Program Counter (PC)
- May be redirected to trap handler if condition is met
Examples
Basic Trap
twi 4, r3, 0 # Trap if r3 == 0 (TO = 4 for equal)
Conditional Trapping
# Trap if value exceeds limit lwz r3, value # Load value twi 12, r3, 100 # Trap if r3 > 100 (TO = 12 for greater than)
Debugging
# Trap for debugging purposes twi 31, r0, 0 # Always trap (TO = 31)