1.4 Instruction Queues

Floating-Point Queue

The floating-point queue contains 16 instruction entries. Up to four instructions may be written during each cycle; newly-decoded floating-point instructions are written into empty entries in random order. Instructions remain in this queue only until they have been issued to a floating-point execution unit.

The floating-point queue controls six dedicated ports to the floating-point register file: two operand read ports and a destination port for each execution unit.

The floating-point queue uses the multiplier's issue port to issue instructions to the square-root and divide units. These instructions also share the multiplier's register ports.

The floating-point queue contains simple sequencing logic for multiple-pass instructions such as Multiply-Add. These instructions require one pass through the multiplier, then one pass through the adder.