Is MOP.R.24 a NOP by default?
Not a pure no-op. It writes zero to rd by default.
MOP.R.24
RISC-V MOP.R.24 Instruction Details
Instruction ManualI-typeZimop MOP.R.24; by default writes zero to rd and may be redefined to read rs1 and write rd.
Instruction Syntax
mop.r.24 rd, rs1
Operand Breakdown
Destination rd: general-purpose register receiving the result.
Source rs1: register holding the first operand.
Immediate imm: 12-bit signed value, sign-extended before operation with rs1.
ZimopSystem & Privileged
Instruction Behavior
MOP.R.24 is a Zimop may-be-operation with recommended syntax mop.r.24 rd, rs1. If no other extension redefines the encoding, the official default behavior writes 0 to x[rd]. The encoding space allows future extensions to define it as reading x[rs1] and writing x[rd]. Standard software should not execute a MOP unless deliberately targeting an extension that redefines it.
Quick Understanding & Search Notes
MOP.R.24 is a Zimop compatible encoding reserved for future extensions; when not redefined, its visible result is rd receiving zero.
The official rule places MOP.R.n encodings in the SYSTEM major opcode.
MOP.R.n allows a future extension to read rs1 and write rd, but by default it does not read rs1.
Common Usage Scenarios
System & Privileged
Understand this scenario with real code like «mop.r.24 t0, t1».
Extension Compatibility
Understand this scenario with real code like «mop.r.24 t0, t1».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is I-type.
- Confirm the operand order matches the example.
Semantic Check
- Ensure the destination register usage is compatible with the calling convention.
- Confirm this is not the lower-level form of a pseudo-instruction expansion.
Pitfalls / Common Confusions
The default is not a true no-register-write NOP; MOP.R.n writes zero to rd by default.
Default Zimop MOPs carry no syntactic dependency from rs1 to rd; a redefining extension may specify otherwise.
Do not confuse Zimop MOP.R.n with Zcmop C.MOP.n, which writes no register by default.
FAQ
Should ordinary software execute MOP.R.24?
No, unless the software deliberately targets an extension that redefines that MOP.