fsm-design

FSM Design Skill

Overview

Specialized skill for finite state machine (FSM) design and optimization, ensuring robust and efficient control logic implementation in FPGA designs.

Capabilities

• Design Moore and Mealy state machines
• Apply state encoding (one-hot, binary, Gray)
• Implement illegal state recovery
• Generate state diagrams and transition tables
• Optimize FSM for area or speed
• Apply safe FSM coding patterns
• Debug FSM behavior with assertions
• Handle FSM with multiple clock domains

Target Processes

• fsm-design.js
• rtl-module-architecture.js
• vhdl-module-development.js
• verilog-systemverilog-design.js

Usage Guidelines

FSM Types

• Moore Machine: Outputs depend only on current state
• Mealy Machine: Outputs depend on state and inputs
• Registered Outputs: Mealy with registered outputs for timing

State Encoding

• One-Hot: Fast, low combinational logic, more flip-flops
• Binary: Compact, minimal flip-flops, more logic
• Gray: Useful for CDC, single-bit transitions
• Custom: For specific optimization requirements

Safe FSM Patterns

• Explicit default state in case statements
• Illegal state detection and recovery
• Synchronous reset to known state
• Avoid latches (cover all cases)
• Use enumerated types for readability

VHDL Style

type state_type is (IDLE, RUN, DONE);
signal state, next_state : state_type;

Verilog Style

localparam [1:0] IDLE = 2'b00, RUN = 2'b01, DONE = 2'b10;
reg [1:0] state, next_state;

Optimization Strategies

• Minimize state bits for area
• One-hot for speed in FPGAs
• Pipeline deep combinational logic
• Consider state splitting for timing

Dependencies

• FSM analysis tools
• Synthesis attribute knowledge
• HDL coding standards