Encoding:

Format:

BALC offset

Purpose:

Branch and Link, Compact

To do an unconditional PC-relative procedure call.

Description:

procedure_call (no delay slot)

Place the return address link in GPR 31. The return link is the address of the instruction immediately following the branch, where execution continues after a procedure call. (Because compact branches have no delay slots, see below.)

A 28-bit signed offset (the 26-bit offset field shifted left 2 bits) is added to the address of the instruction following the branch (not the branch itself), to form a PC-relative effective target address.

Compact branches do not have delay slots. The instruction after the branch is NOT executed when the branch is taken.

Restrictions:

This instruction is an unconditional, always taken, compact branch. It does not have a forbidden slot, that is, a

Reserved Instruction exception is not caused by a Control Transfer Instruction placed in the slot following the branch.

Availability and Compatibility:

This instruction is introduced by and required as of Release 6.

Release 6 instruction BALC occupies the same encoding as pre-Release 6 instruction SWC2. The SWC2 instruction has been moved to the COP2 major opcode in MIPS Release 6.

Exceptions:

None

Operation:

target_offset = sign_extend( offset || 02 )
GPR[31] = PC+4
PC = PC+4 + sign_extend(target_offset)