Instruction-level parallelism (ILP) is a measure of how
many of the operations in a computer program can be performed simultaneously.
Superscalar techniques based on extracting instruction-level parallelism have
been a major contribution to high performance microprocessor design throughout
the last decade. The number of instructions executed per cycle (IPC) is
increased substantially through superscalar techniques like speculative
execution and dynamic scheduling. While speculative execution deals with control
dependencies, dynamic scheduling processes data dependencies and leverages the
stalls due to dependencies through out-of-order execution. The out-of-order
issue logic identifies if instruction operands are ready and selects the highest
priority ready instructions for execution. Despite these advantages however,
there is still demand for more efficient and less complex methods to resolve
issue logic complexity.
Researchers at Arizona State University have developed a new
method to reduce issue logic complexity. They have developed a novel issue logic
implementation that divides the instruction ready signals into groups and
selects the four highest priority instructions. By splitting the ready signals
into groups and processing them in parallel, the complexity of issuing multiple
instructions is reduced. The oldest first priority selection is used and the
wakeup, update and select operations are completed in a single cycle ensuring
high instructions per cycle (IPC). The select and update logic are implemented
using static combinational logic that aids in borrowing time from wakeup logic.
The design is implemented entirely in static CMOS circuits to reduce the power
dissipation and provide ease of implementation as well as process portability.
The method also reduces low fan out and improves circuit speed.
Microprocessor manufacturers such as:
- Advanced Micro Devices (AMD)
- Broadcom Corporation
- Less power consumption
- Faster circuit speed
- Simple architecture
- Ease of implementation
- Process portability