mftb

Move From Timebase

mftb RT,268

Moves the contents of the Time Base Register (TBR) into a general-purpose register.

Encoding

Binary Layout

31

0:5

RT

6:10

268

11:20

371

21:30

/

31

 

Format XFX-form

Opcode 0x7C0002E6

Extension Base

Operands

• RT
  Target

Example

mftb r3, 268

Registers Altered

TBR

Related

Across architectures

Read Cycle Counter : how x86, ARM, RISC-V, and PowerISA each do this.

More in Base

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

This instruction behaves as if it were an mfspr instruction. The TBR operand is omitted and assumed to be 268 (the value that corresponds to TB).

Operation

if 'mftb' then
    RT <- TBR[268]

Extended Mnemonics

Extended Mnemonic
mftb RT
mfspr RT,268

The source lists these forms without stating the instruction each one stands for.

Programming Note

This instruction behaves as if it were an mfspr instruction; see the mfspr instruction description in Section 3.3.19 of Book I. New programs should use mfspr instead of mftb to access the Time Base.