Intel® Quartus® Prime Standard Edition User Guide: Design Recommendations

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ID 683323
Date 9/24/2018
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Document Table of Contents
Document Table of Contents x
1. Recommended Design Practices 2. Recommended HDL Coding Styles 3. Managing Metastability with the Intel® Quartus® Prime Software A. Intel® Quartus® Prime Standard Edition User Guides
1. Recommended Design Practices x
1.1. Following Synchronous FPGA Design Practices 1.2. HDL Design Guidelines 1.3. Checking Design Violations 1.4. Use Clock and Register-Control Architectural Features 1.5. Implementing Embedded RAM 1.6. Recommended Design Practices Revision History
1.1. Following Synchronous FPGA Design Practices x
1.1.1. Implementing Synchronous Designs 1.1.2. Asynchronous Design Hazards
1.2. HDL Design Guidelines x
1.2.1. Optimizing Combinational Logic 1.2.2. Optimizing Clocking Schemes 1.2.3. Optimizing Physical Implementation and Timing Closure 1.2.4. Optimizing Power Consumption 1.2.5. Managing Design Metastability
1.2.1. Optimizing Combinational Logic x
1.2.1.1. Avoid Combinational Loops 1.2.1.2. Avoid Unintended Latch Inference 1.2.1.3. Avoid Delay Chains in Clock Paths 1.2.1.4. Use Synchronous Pulse Generators
1.2.2. Optimizing Clocking Schemes x
1.2.2.1. Register Combinational Logic Outputs 1.2.2.2. Avoid Asynchronous Clock Division 1.2.2.3. Avoid Ripple Counters 1.2.2.4. Use Multiplexed Clocks 1.2.2.5. Use Gated Clocks 1.2.2.6. Use Synchronous Clock Enables
1.2.2.5. Use Gated Clocks x
1.2.2.5.1. Recommended Clock-Gating Methods
1.2.3. Optimizing Physical Implementation and Timing Closure x
1.2.3.1. Planning Physical Implementation 1.2.3.2. Planning FPGA Resources 1.2.3.3. Optimizing for Timing Closure 1.2.3.4. Optimizing Critical Timing Paths
1.3. Checking Design Violations x
1.3.1. Validating Against Design Rules 1.3.2. Creating Custom Design Rules
1.3.2. Creating Custom Design Rules x
1.3.2.1. Custom Design Rule Examples
1.4. Use Clock and Register-Control Architectural Features x
1.4.1. Use Global Reset Resources 1.4.2. Use Global Clock Network Resources 1.4.3. Use Clock Region Assignments to Optimize Clock Constraints 1.4.4. Avoid Asynchronous Register Control Signals
1.4.1. Use Global Reset Resources x
1.4.1.1. Use Synchronous Resets 1.4.1.2. Using Asynchronous Resets 1.4.1.3. Use Synchronized Asynchronous Reset
1.4.3. Use Clock Region Assignments to Optimize Clock Constraints x
1.4.3.1. Clock Region Assignments in Intel® Arria® 10 and Older Device Families
2. Recommended HDL Coding Styles x
2.1. Using Provided HDL Templates 2.2. Instantiating IP Cores in HDL 2.3. Inferring Multipliers and DSP Functions 2.4. Inferring Memory Functions from HDL Code 2.5. Register and Latch Coding Guidelines 2.6. General Coding Guidelines 2.7. Designing with Low-Level Primitives 2.8. Recommended HDL Coding Styles Revision History
2.1. Using Provided HDL Templates x
2.1.1. Inserting HDL Code from a Provided Template
2.3. Inferring Multipliers and DSP Functions x
2.3.1. Inferring Multipliers 2.3.2. Inferring Multiply-Accumulator and Multiply-Adder Functions
2.4. Inferring Memory Functions from HDL Code x
2.4.1. Inferring RAM functions from HDL Code 2.4.2. Inferring ROM Functions from HDL Code Verilog HDL Synchronous ROM VHDL Synchronous ROM Verilog HDL Dual-Port Synchronous ROM Using readmemb VHDL Dual-Port Synchronous ROM Using Initialization Function 2.4.3. Inferring Shift Registers in HDL Code
2.4.1. Inferring RAM functions from HDL Code x
2.4.1.1. Use Synchronous Memory Blocks 2.4.1.2. Avoid Unsupported Reset and Control Conditions 2.4.1.3. Check Read-During-Write Behavior 2.4.1.4. Controlling RAM Inference and Implementation 2.4.1.5. Single-Clock Synchronous RAM with Old Data Read-During-Write Behavior 2.4.1.6. Single-Clock Synchronous RAM with New Data Read-During-Write Behavior 2.4.1.7. Simple Dual-Port, Dual-Clock Synchronous RAM 2.4.1.8. True Dual-Port Synchronous RAM 2.4.1.9. Mixed-Width Dual-Port RAM 2.4.1.10. RAM with Byte-Enable Signals 2.4.1.11. Specifying Initial Memory Contents at Power-Up
2.4.3. Inferring Shift Registers in HDL Code x
2.4.3.1. Simple Shift Register 2.4.3.2. Shift Register with Evenly Spaced Taps
2.5. Register and Latch Coding Guidelines x
2.5.1. Register Power-Up Values 2.5.2. Secondary Register Control Signals Such as Clear and Clock Enable 2.5.3. Latches
2.5.1. Register Power-Up Values x
2.5.1.1. Specifying a Power-Up Value
2.5.3. Latches x
2.5.3.1. Avoid Unintentional Latch Generation 2.5.3.2. Inferring Latches Correctly
2.6. General Coding Guidelines x
2.6.1. Tri-State Signals 2.6.2. Clock Multiplexing 2.6.3. Adder Trees 2.6.4. State Machine HDL Guidelines 2.6.5. Multiplexer HDL Guidelines 2.6.6. Cyclic Redundancy Check Functions 2.6.7. Comparator HDL Guidelines 2.6.8. Counter HDL Guidelines
2.6.3. Adder Trees x
2.6.3.1. Architectures with 4-Input LUTs in Logic Elements 2.6.3.2. Architectures with 6-Input LUTs in Adaptive Logic Modules
2.6.4. State Machine HDL Guidelines x
2.6.4.1. Verilog HDL State Machines 2.6.4.2. VHDL State Machines
2.6.4.1. Verilog HDL State Machines x
2.6.4.1.1. Verilog-2001 State Machine Coding Example 2.6.4.1.2. SystemVerilog State Machine Coding Example
2.6.4.2. VHDL State Machines x
2.6.4.2.1. VHDL State Machine Coding Example
2.6.5. Multiplexer HDL Guidelines x
2.6.5.1. Intel® Quartus® Prime Software Option for Multiplexer Restructuring 2.6.5.2. Multiplexer Types 2.6.5.3. Implicit Defaults in IF Statements 2.6.5.4. default or OTHERS CASE Assignment
2.6.5.2. Multiplexer Types x
2.6.5.2.1. Binary Multiplexers 2.6.5.2.2. Selector Multiplexers 2.6.5.2.3. Priority Multiplexers
2.6.6. Cyclic Redundancy Check Functions x
2.6.6.1. If Performance is Important, Optimize for Speed 2.6.6.2. Use Separate CRC Blocks Instead of Cascaded Stages 2.6.6.3. Use Separate CRC Blocks Instead of Allowing Blocks to Merge 2.6.6.4. Take Advantage of Latency if Available 2.6.6.5. Save Power by Disabling CRC Blocks When Not in Use 2.6.6.6. Initialize the Device with the Synchronous Load (sload) Signal
3. Managing Metastability with the Intel® Quartus® Prime Software x
3.1. Metastability Analysis in the Intel® Quartus® Prime Software 3.2. Metastability and MTBF Reporting 3.3. MTBF Optimization 3.4. Reducing Metastability Effects 3.5. Scripting Support 3.6. Managing Metastability 3.7. Managing Metastability with the Intel® Quartus® Prime Software Revision History
3.1. Metastability Analysis in the Intel® Quartus® Prime Software x
3.1.1. Synchronization Register Chains 3.1.2. Identify Synchronizers for Metastability Analysis 3.1.3. How Timing Constraints Affect Synchronizer Identification and Metastability Analysis
3.2. Metastability and MTBF Reporting x
3.2.1. Metastability Reports 3.2.2. Synchronizer Data Toggle Rate in MTBF Calculation
3.2.1. Metastability Reports x
3.2.1.1. MTBF Summary Report 3.2.1.2. Synchronizer Summary Report 3.2.1.3. Synchronizer Chain Statistics Report in the Timing Analyzer
3.2.1.1. MTBF Summary Report x
3.2.1.1.1. Typical and Worst-Case MTBF of Design 3.2.1.1.2. Synchronizer Chains 3.2.1.1.3. Increasing Available Settling Time
3.3. MTBF Optimization x
3.3.1. Synchronization Register Chain Length
3.4. Reducing Metastability Effects x
3.4.1. Apply Complete System-Centric Timing Constraints for the Timing Analyzer 3.4.2. Force the Identification of Synchronization Registers 3.4.3. Set the Synchronizer Data Toggle Rate 3.4.4. Optimize Metastability During Fitting 3.4.5. Increase the Length of Synchronizers to Protect and Optimize 3.4.6. Set Fitter Effort to Standard Fit instead of Auto Fit 3.4.7. Increase the Number of Stages Used in Synchronizers 3.4.8. Select a Faster Speed Grade Device
3.5. Scripting Support x
3.5.1. Identifying Synchronizers for Metastability Analysis 3.5.2. Synchronizer Data Toggle Rate in MTBF Calculation 3.5.3. report_metastability and Tcl Command 3.5.4. MTBF Optimization 3.5.5. Synchronization Register Chain Length
1. Recommended Design Practices
2. Recommended HDL Coding Styles
3. Managing Metastability with the Intel® Quartus® Prime Software
A. Intel® Quartus® Prime Standard Edition User Guides

2.4.2. Inferring ROM Functions from HDL Code

Synthesis tools infer ROMs when a CASE statement exists in which a value is set to a constant for every choice in the CASE statement.

Because small ROMs typically achieve the best performance when they are implemented using the registers in regular logic, each ROM function must meet a minimum size requirement for inference and placement in memory.

Note: If you use Intel® Quartus® Prime Standard Edition integrated synthesis , you can direct the Intel® Quartus® Prime software to infer ROM blocks for all sizes with the Allow Any ROM Size for Recognition option in the Advanced Analysis & Synthesis Settings dialog box.

Some synthesis tools provide options to control the implementation of inferred ROM blocks for Intel FPGA devices with synchronous memory blocks. For example, Intel® Quartus® Prime Standard Edition integrated synthesis provides the romstyle synthesis attribute to specify the type of memory block or to specify the use of regular logic instead of a dedicated memory block.

For device architectures with synchronous RAM blocks, such as the Arria®  series, Cyclone®  series, or Stratix®  series devices, to infer a ROM block, synthesis must use registers for either the address or the output. When your design uses output registers, synthesis implements registers from the input registers of the RAM block without affecting the functionality of the ROM. If you register the address, the power-up state of the inferred ROM can be different from the HDL design. In this scenario, Intel® Quartus® Prime synthesis issues a warning.

The following ROM examples map directly to the Intel FPGA memory architecture.

Verilog HDL Synchronous ROM

module sync_rom (clock, address, data_out);
	input clock;
	input [7:0] address;
	output reg [5:0] data_out;
	reg [5:0] data_out;

	always @ (posedge clock)
	begin
		case (address)
			8'b00000000: data_out = 6'b101111;
			8'b00000001: data_out = 6'b110110;
			...
			8'b11111110: data_out = 6'b000001;
			8'b11111111: data_out = 6'b101010;
		endcase
	end
endmodule

VHDL Synchronous ROM

LIBRARY ieee;
USE ieee.std_logic_1164.all;

ENTITY sync_rom IS
	PORT (
		clock: IN STD_LOGIC;
		address: IN STD_LOGIC_VECTOR(7 downto 0);
		data_out: OUT STD_LOGIC_VECTOR(5 downto 0)
	);
END sync_rom;

ARCHITECTURE rtl OF sync_rom IS
BEGIN
PROCESS (clock)
	BEGIN
	IF rising_edge (clock) THEN
		CASE address IS
			WHEN "00000000" => data_out <= "101111";
			WHEN "00000001" => data_out <= "110110";
			...
			WHEN "11111110" => data_out <= "000001";
			WHEN "11111111" => data_out <= "101010";
			WHEN OTHERS     => data_out <= "101111";
		END CASE;
	END IF;
	END PROCESS;
END rtl;

Verilog HDL Dual-Port Synchronous ROM Using readmemb

module dual_port_rom
#(parameter data_width=8, parameter addr_width=8)
(
	input [(addr_width-1):0] addr_a, addr_b,
	input clk, 
	output reg [(data_width-1):0] q_a, q_b
);
	reg [data_width-1:0] rom[2**addr_width-1:0];

	initial // Read the memory contents in the file
			 //dual_port_rom_init.txt. 
	begin
		$readmemb("dual_port_rom_init.txt", rom);
	end

	always @ (posedge clk)
	begin
		q_a <= rom[addr_a];
		q_b <= rom[addr_b];
	end
endmodule

VHDL Dual-Port Synchronous ROM Using Initialization Function 

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity dual_port_rom is
	generic (
		DATA_WIDTH : natural := 8;
		ADDR_WIDTH : natural := 8
	);
	port (
		clk     : in std_logic;
		addr_a  : in natural range 0 to 2**ADDR_WIDTH - 1;
		addr_b  : in natural range 0 to 2**ADDR_WIDTH - 1;
		q_a     : out std_logic_vector((DATA_WIDTH -1) downto 0);
		q_b     : out std_logic_vector((DATA_WIDTH -1) downto 0)
	);
end entity;

architecture rtl of dual_port_rom is
	-- Build a 2-D array type for the ROM
	subtype word_t is std_logic_vector((DATA_WIDTH-1) downto 0);
	type memory_t is array(2**ADDR_WIDTH - 1 downto 0) of word_t;

	function init_rom
		return memory_t is 
		variable tmp : memory_t := (others => (others => '0'));
	begin 
		for addr_pos in 0 to 2**ADDR_WIDTH - 1 loop 
			-- Initialize each address with the address itself
			tmp(addr_pos) := std_logic_vector(to_unsigned(addr_pos, DATA_WIDTH));
		end loop;
		return tmp;
	end init_rom;	 

	-- Declare the ROM signal and specify a default initialization value.
	signal rom : memory_t := init_rom;
begin
	process(clk)
	begin
	if (rising_edge(clk)) then
		q_a <= rom(addr_a);
		q_b <= rom(addr_b);
	end if;
	end process;
end rtl;
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