tbegin.

Transaction Begin

tbegin. R

Initiates a hardware transaction. If the transaction fails, execution rolls back to this point. Sets CR0 based on success/failure.

Encoding

Binary Layout

31

0:5

/

6:10

R

11:15

/

16:20

654

21:30

1

31

 

Format X-form

Opcode 0x7C00051D

Extension Transactional Memory

Operands

• R
  Rollback Handler (0=External, 1=Internal)

Example

tbegin. 0

// Start atomic hardware transaction.

Registers Altered

CR0

Related

More in Transactional Memory

Reference

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

Description

Initiates a hardware transaction, setting the transaction active state and recording checkpoint information. If execution completes successfully within the transaction, tbegin. sets CR0[EQ] = 1; if the transaction is aborted, execution rolls back to this instruction and CR0[EQ] = 0, with CR0[SO] indicating the abort cause. The R field determines whether a transaction failure causes an external rollback (R=0) or an internal retry (R=1). Requires Transactional Memory (TM) facility support.

Operation

if transaction initiated successfully then CR0[EQ] ← 1 else CR0[EQ] ← 0; CR0[LT,GT,SO] set based on abort cause; transaction state is active

Programming Note

In synthetic TM mode, transactions initiated by tbegin will fail immediately, invoking the failure handler. Ensure that your application logic correctly handles transaction failures to maintain data integrity.