mftbu

Move From Timebase Upper

mftbu RT

Reads the upper 32 bits of the Timebase (32-bit implementations).

Encoding

Binary Layout

31

0:5

RT

6:10

269

11:20

371

21:30

/

31

 

Format XFX-form

Opcode 0x7C0002E7

Extension Base

Operands

• RT
  Target

Example

mftbu r3

Registers Altered

TBU

Related

More in Base

Reference

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

Description

Reads the upper 32 bits of the Timebase register and places the value into the target GPR. This instruction is primarily used in 32-bit implementations to obtain the high word of the 64-bit Timebase. It does not modify condition registers or status fields.

Operation

RT ← TBU
// TBU is the upper 32 bits of the 64-bit Timebase counter

Programming Note

Use mftbu to capture the high-order bits of the timebase for timestamping or performance measurement. Ensure that your application accounts for potential discrepancies between the upper and lower 32-bit reads due to timebase overflow.