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Verilog Design Methodology for Pinball Machine

Learn the Verilog design methodology for a Pinball Machine with state transition diagrams, coding, states, and examples. Understand how to map combinational and sequential blocks in Verilog. Discover the evolution of Verilog code and module declaration.

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Verilog Design Methodology for Pinball Machine

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  1. 332:437 Lecture 9 Verilog Example • Verilog Design Methodology • Pinball Machine • Verilog Coding • States • State transition diagram • Final Verilog Code • Summary Bushnell: Digital Systems Design Lecture 9

  2. Verilog Design Methodology • Draw a System Block Diagram • As if you were designing the hardware by hand • Label all signals • For each block: • Determine whether it is controlled by clocks or reset signals • If so, it is sequential • If not, it is combinational Bushnell: Digital Systems Design Lecture 9

  3. Verilog Design Methodology • Combinational blocks • Map into combinational always block or into assign statement • Sequential blocks • Map into always block controlled by: • {posedge, negedge} clk • {posedge, negedge} reset, set Bushnell: Digital Systems Design Lecture 9

  4. Verilog Design Methodology • Add an initial block for the testbench • Add additional always block to generate the clock • Add additional sequential always blocks for every counter Bushnell: Digital Systems Design Lecture 9

  5. Example -- Design a Pinball Machine • After left-flipper or right-flipper pressed • If ball in 100 point slot, + 100 pt (green) • If ball in 200 point slot, + 200 pt (yellow) • If 3 200 point hits in a row, enable big_bopper slot (red) • If big_bopper slot enabled and hit (gold), • Get 600 points • Increment free_game count • If ball_lost, go back to start state Bushnell: Digital Systems Design Lecture 9

  6. green yellow red Gold bop_en 100 200 bop_hit Next State Decoder Output Decoder pgames Game Counter 100 200 bop_hit Testbench Clock Generator ppoints Point Counter State Register Hardware Visualization Bushnell: Digital Systems Design Lecture 9

  7. State Transition Diagram • Need these states: • init – initialize the machine • start – waiting for input • h200one – hit 200 point hole once • h200two – hit 200 point hole twice • h200three – hit 200 point hole 3 X Bushnell: Digital Systems Design Lecture 9

  8. Verilog Coding • Write an always block for each box on the prior slide • One exception – combine next state and output decoders into 1 always block • Why? • For clarity • Less code to write • Guaranteed that both decoders activate under same conditions Bushnell: Digital Systems Design Lecture 9

  9. h200one init h200two start h200three State Transition Diagram ball_lost neither ball_lost neither h200 h100 h100 h100 ball_lost h200 h100 ball_lost h200 neither bop_hit h200 neither Bushnell: Digital Systems Design Lecture 9

  10. Evolution of Verilog Code • Combined next state and output decoders into one always block for clarity • design_analyzer objected to clock generator process – moved it to the testbench • Forgot to code hardware for bop_enable – fixed that • vcs objected to the @(*) sensitivity list of clock generator – combined it with rest of testbench • Corrected testbench and it worked! Bushnell: Digital Systems Design Lecture 9

  11. Module Declaration module pinballmachine (input clk, reset_bar, output reg [0:2] pstate, output reg [0:2] nstate, output reg [0:4] games, output reg [0:15] points, output reg [0:4] pgames, output reg [0:15] ppoints, input h100, h200, bop_hit, ball_lost, output reg bop_en, green, yellow, red, gold); Bushnell: Digital Systems Design Lecture 9

  12. Declaration of states parameter init = 0, start = 1, h200one = 2, h200two = 3, h200three = 4; Bushnell: Digital Systems Design Lecture 9

  13. State Flip-flops // State flipflopsalways @(posedge clk, negedge reset_bar) begin if (reset_bar == 0) pstate <= init; else pstate <= nstate; end Bushnell: Digital Systems Design Lecture 9

  14. Next State/Output Decoder // Next state and output decoderalways @(*) begin case (pstate) init: begin nstate <= start; points <= 0; games <= 0; green <= 0; yellow <= 0; red <= 0; gold <= 0; bop_en <= 0; end Bushnell: Digital Systems Design Lecture 9

  15. Next State/Output Decoder start:begin bop_en <= 0; if (! ball_lost) begin if (h100 == 1) begin nstate <= start; points <= ppoints + 100; games <= 0; green <= 1; yellow <= 0; red <= 0; gold <= 0; end Bushnell: Digital Systems Design Lecture 9

  16. Next State/Output Decoder else if (h200 == 1) begin nstate <= h200one; points <= ppoints + 200; games <= 0; green <= 0; yellow <= 1; red <= 0; gold <= 0; end else begin nstate <= start; points <= 0; games <= 0; end end Bushnell: Digital Systems Design Lecture 9

  17. Next State/Output Decoder else begin nstate <= start; points <= 0; games <= 0; green <= 0; yellow <= 0; red <= 0; gold <= 0; end end Bushnell: Digital Systems Design Lecture 9

  18. Next State/Output Decoder h200one: begin bop_en <= 0; if (! ball_lost) begin if (h100 == 1) begin nstate <= start; points <= ppoints + 100; games <= 0; green <= 1; yellow <= 0; red <= 0; gold <= 0; end Bushnell: Digital Systems Design Lecture 9

  19. Next State/Output Decoder else if (h200 == 1) begin nstate <= h200two; points <= ppoints + 200; games <= 0; green <= 0; yellow <= 1; red <= 0; gold <= 0; end else begin nstate <= h200one; points <= 0; games <= 0; end end Bushnell: Digital Systems Design Lecture 9

  20. Next State/Output Decoder else begin nstate <= start; points <= 0; games <= 0; green <= 0; yellow <= 0; red <= 0; gold <= 0; end end Bushnell: Digital Systems Design Lecture 9

  21. Next State/Output Decoder h200two: begin if (! ball_lost) begin if (h100 == 1) begin nstate <= start; points <= ppoints + 100; games <= 0; green <= 1; yellow <= 0; red <= 0; gold <= 0; bop_en <= 0; end Bushnell: Digital Systems Design Lecture 9

  22. Next State/Output Decoder else if (h200 == 1) begin nstate <= h200three; points <= ppoints + 200; games <= 0; green <= 0; yellow <= 0; red <= 1; gold <= 0; bop_en <= 1; end else begin nstate <= h200two; points <= 0; games <= 0; end end Bushnell: Digital Systems Design Lecture 9

  23. Next State/Output Decoder else begin nstate <= start; points <= 0; games <= 0; green <= 0; yellow <= 0; red <= 0; gold <= 0; bop_en <= 0; end end Bushnell: Digital Systems Design Lecture 9

  24. Next State/Output Decoder h200three: begin if (! ball_lost) begin if (h100 == 1) begin nstate <= start; points <= ppoints + 100; games <= 0; green <= 1; yellow <= 0; red <= 0; gold <= 0; bop_en <= 0; end Bushnell: Digital Systems Design Lecture 9

  25. Next State/Output Decoder else if (h200 == 1) begin nstate <= start; points <= ppoints + 200; games <= 0; green <= 0; yellow <= 1; red <= 0; gold <= 0; bop_en <= 0; end Bushnell: Digital Systems Design Lecture 9

  26. Next State/Output Decoder else if (bop_hit == 1) begin nstate <= start; points <= ppoints + 600; games <= pgames + 1; green <= 0; yellow <= 0; red <= 0; gold <= 1; bop_en <= 0; end Bushnell: Digital Systems Design Lecture 9

  27. Next State/Output Decoder else begin nstate <= h200three; points <= 0; games <= 0; end end else begin nstate <= start; points <= 0; games <= 0; green <= 0; yellow <= 0; red <= 0; gold <= 0; bop_en <= 0; end end endcase end Bushnell: Digital Systems Design Lecture 9

  28. Point Counter // Point counteralways @(posedge clk, negedge reset_bar) begin if (reset_bar == 0) ppoints <= 0; else if (points) ppoints <= points; end Bushnell: Digital Systems Design Lecture 9

  29. Game Counter // Game counteralways @(posedge clk, negedge reset_bar) begin if (reset_bar == 0) pgames <= 0; else if (games) pgames <= games; endendmodule Bushnell: Digital Systems Design Lecture 9

  30. system Module module system (); wire clk; wire reset_bar; wire [0:2] pstate; wire [0:2] nstate; wire [0:4] games; wire [0:15] points; wire [0:4] pgames; wire [0:15] ppoints; wire h100, h200, bop_hit, ball_lost; wire bop_en; wire green, yellow, red, gold; pinballmachine (clk, reset_bar, pstate, nstate, games, points, pgames, ppoints, h100, h200, bop_hit, ball_lost, bop_en, green, yellow, red, gold); testbench (clk, reset_bar, pstate, nstate, games, points, pgames, ppoints, h100, h200, bop_hit, ball_lost, bop_en, green, yellow, red, gold);endmodule Bushnell: Digital Systems Design Lecture 9

  31. Summary • Still need to visualize the hardware as combinational and sequential blocks in block diagram when using Verilog • Still need to design tight state transition diagram • Blocks in diagram translate into always/assign statements Bushnell: Digital Systems Design Lecture 9

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