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Guideline 3:- All the IO’s should be properly constrained during synthesis and layout to avoid setup or hold time violations.

Diagram to show routing of data across FPGA’s and requirements for doing Static Timing Analysis

Guideline 4:- Implementing clock domain crossing is the most complicated design scenario in digital circuits. Necessary steps to design involves detailed analysis of the clocks across the domain.

Following are some ideas to implement clock domain crossing: Use rate – change FIFO, Double clocking, Gray encoders for counters.

Guideline 5:- Wires and Registers should be correctly implemented in Verilog. Registers must be used within always blocks. Wires are used for connectivity outside always blocks and are generally used with assign statements or for connectivity not requiring any registered delay.   

Guideline 6: Blocking vs. non-blocking stms.

Blocking statements are always used within combinatory block to execute statements in a sequence. Non – blocking statements are always executed in a sequential logic block to execute all statements in at either clock edge.

Guideline 7: Never mix blocking and non-blocking stms in a single always block in Verilog. 

RTL Coding guidelines for ASIC/FPGA implementations

Guideline 1:- Declare every possible state in conditional statements. Missing a declaration can result in un-intentional latches in design.

Example

           if (condition True)

              d_ff <= ’b1; 

          else

              d_ff <= ‘b0;

Guideline 2:- All the signals coming to/from external world should be properly registered to avoid setup time violations.

Guideline 9:- After simulating the design, always synthesize it and check for latches, unbounded component,  tri-state logic etc.

Guideline 10: - Conditional IF statements should not be used in parallel states. Case statements best

Guideline 8:-  Suggested approach to write synthesizable RTL is to separate the synchronous and combinational logic into separate processes (always blocks in Verilog).