@c alus.botex
@c
@c 21-May-88, James Rauen

@chapter ALUs
@label[OREG]

The processor's main ALU is Advanced Micro Devices' Am29332 Arithmetic
Logic Unit.  For a complete specification of its behavior, consult the
29332's documentation.  A summary of the ALU's opcodes appears in the
ALU Opcodes chapter.

An ALU operation is determined by the ALU Opcode and Byte Width fields
of an instruction.  Bit operations might also require the Shift and Mask
fields.

The board set is also designed to use Weitek floating point hardware.
However, this design had to be abandoned because the state of the Weitek
hardware cannot be saved and restored during trap entry/exit.

The left and right inputs to the ALUs are determined by the Left Source and
Right Source fields of an instruction.  The ALU output is registered in OREG,
the ALU output register.