Adding RESET button to ispMACH 4256ZE Breakout Board

It may sound strange (especially for IT crowd :-) - but this board/circuit has no RESET pin nor RESET button. It is expected to use one of Input pins for RESET if needed.

To use this tutorial you should have working hardware and software as described in Getting started with ispMACH 4256ZE Breakout Board

Creating RESET button/circuit

Adding RESET hardware

The RESET circuit is taken from Lattice Pico Development board. Schematic is as follows (I used 100 based index to avoid confusion with official Break Board schematic).:

NOTE: all signal names match PCB bottom silkscreen names.

There is nothing surprising. The capacitor C100 is used to create short RESET signal on Power-Up (and it may also help de-bouncing contacts - maybe).

Please note that this RESET signal is negative - meaning:

• logical 0 => RESET is active (button pushed, or short pulse on power-up)
• logical 1 => RESET is inactive (button released)

Finished Break Board with RESET button is on pictures bellow:

NOTE for wire colors:

• blue -> connected to GND (Ground)
• red -> connected to VCC0_EXT_0 (+3.3V supply - default on this board)
• orange -> connected to IN 72 pin (used for our RESET input)

Important information on Voltage:

There are two important distinct rules:

1. Output pin voltage levels are hardwired by VCCO pins for Banks. The default is 3.3V and can be measured on TP1 point (for Bank0) And TP2 point (for Bank1)
2. Input pint voltage is individually selectable in Constraint Editor

Summary:

1. For Output pins you don't need to worry - voltage is hardwired on board
2. For Input pins always verify selected voltages on Constraint Editor for each input pin

Creating test project

Now when we have RESET button we should test it - we shall create trivial project that would show:

• RESET state on LED D1
• inverted RESET state on LED D2

To create new project do the following:

• create initial Verilog HDL file c:\projects\res_test.v with this content:

// trivial RESET button test
module res_test (led,nrst);
  output [1:0] led;
  input nrst;

  assign led[0] = nrst;
  assign led[1] = !led[0];

endmodule

NOTE: nrst is shortcut for "Negative RESET" meaning that RESET is active when logical '0' and inactive in logical '1'.

NOTE2: If you are curious you should ask - how D1 works - when our RESET is negative (shouldn't also D1 invert this signal before output?).

It is very simple - attached LED D1 - D8 also use negative logic (they light when there is logic 0 on ispMach CPLD output. And so negation of negation cancel each other.

• run ispLEVER CLASSIC 2.0
• click on File -> New Project...
• Fill in:
  • Project Name: res_test
  • Location: c:\projects\res_test
  • Design Entry Type: Verilog HDL
  • Synthesis Tool: Synplify
  • Simulator Tools: Active-HDL
• click on Next
• select following:
  • Family: ispMACH 4000
  • Device: LC4256ZE
  • Speed Grade: -5.8
  • Package Type: 144TQFP
  • Operating Conditions: Commercial (the only option in my case)
  • Part Name (just check): LC4256ZE-5TN144C (should be same as name of Lattice chip on PCB)
• click on Next
• click on Add Source... button
  • select file c:\projects\res_test.v
  • keep "Type of Source": Verilog Module
  • click on OK
• check on Copy Source to Work Directory
• click on Next
• click on Finish to confirm project information

Defining Input & Output PINS:

• Ensure that of "Yellow chip icon" is elected
• In Process window double-click on "Constraint Editor"
• wait a while (it will compile our Verilog HDL file first) until Constraint Editor appears
• to connect Input PIN to our RESET circuit:
  • expand res_test -> Input Pins -> nrst - and double-click on nrst
    • type 72 in Pin cell
    • I/O type change to: LVCMOS33 - very important - unlike outputs (which voltage is hardwire to voltage on VCCO pin of corresponding bank) - input voltage is defined programmatically in in constraint editor!
    • on "Pull" select OFF (we have our own Pull-UP resistor in RESET Circuit)
• to connect output LED D1:
  • expand and double-click on res_tests -> Output Pins -> led(1:0) -> led_0_
  • fill in:
    • Pin: 71 (see ispMACH4256ZEBreakoutBoardEvaluationKitUsersGuide.PDF "Figure 6. J1 Header Landing and LED Array Callout" to verify.
    • Pull: OFF (maybe not needed?)
• to connect output LED D2:
  • expand and double-click on res_tests -> Output Pins -> led(1:0) -> led_1_
  • fill in:
    • Pin: 70 (see ispMACH4256ZEBreakoutBoardEvaluationKitUsersGuide.PDF "Figure 6. J1 Header Landing and LED Array Callout" to verify.
    • Pull: OFF (maybe not needed?)
• press Ctrl-S to save Constraints
• return back to ispLEVER
• ensure that "Yellow chip" icon text is selected
• double-click on Fit Design in Processes Window It should build project without errors.

Creating new project in ispVM

• run ispVM 17.9
• click on "Close" if you have opened existing project.
• click on File/New
• click on Options -> "Cable and I/O Port Setup"
• ensure that are set:
  • Cable Type: USB2
  • Port Setting: FTUSB-0

• click on OK
• press F2 to do ispTools -> Scan Chain
• our LC4256ZE should appear
• right-click on it and elect "Edit Device"
• click on "Browse..." and select existing c:\projects\res_test\res_test.jed
• click on "OK"
• click on Ctrl-S to save configuration
• fill pathanme like c:\projects\res_test\bboard.xcf

To programm connected Kit:

• press Ctrl-G to programm device = Project -> Download

If everything is OK than:

• LED D2 should be lighting
• LED D1 should be off

When button is pressed than both LEDs should Flip (D1 on, D2 off).

Simulate (Test) our Verilog HDL module

To simulate input (called stimulus) and output we need to create so called "test fixture". We need to:

• select source file [res_test (res_test.v)] in "Sources in Project:" Window
• double click on "Verilog Tet Fixture Template" in "Processes ..." Window
• now rename (for example in TotalCmd) generated file res_test.tft to res_test_tf.v
• now click on Source -> Import ...
• and import file res_test_tf.v
• change Type of Source: to Verilog Test Fixture
• click on OK
• in "Associate with" you can keep highlighted our Device Name (LC4256ZE-....)
• now right-click "res_test_tf.v" in "Sources in Project" Window
• click on "Open"
• add to last initial begin block:

    initial begin
            nrst = 0;
        #300 nrst = 1;
        #300 nrst = 0;
    end

• in 300 time-units we changed nrst from 0 to 1, and after another 300 time units we change it back. By default there is timeunit timescale 1 ns / 1 ns (= timeunit is 1ns with precision 1ns) so it does mean:
  • in 0ns nrst = 0
  • in 300ns nrst = 1
  • in 600ns nrst = 0
• Active-HDL simulate 1uS in total - so we tried to change our values evenly (only roughly :-)
• save that modified file (Ctrl-S)

Having source file "res_test_tf.v" still selected you can now try to double-click on one of available Process links:

• Aldec Verilog Functional Simulation
• Aldec Verilog Timing Simulation

There is very important differnce between these two:

• The Functional simulation does not simulate real gate delays (you can see that led output are changed immediately after nrst change)
• The Timing simulation simulate even gate delays (there is visible that led output follows nrst change).

See bellow screenshot from Timing simulation (with delays):

files/a-hdl-timing-simu.png

Running light with RESET

Now we will utilize our RESET circuit in running LED D5-D8. It uses cyclic shift register which will not work without proper initialization.

To program running light do:

• change res_test.v to:

//  RESET button with running light on LED D5-D8 (aled)
module res_test (led,aled,nrst);
  output [1:0] led;  // two FLIP LEDs D1, D2
  output [3:0] aled; // Animated LED  D5-D8
  input nrst;        // RESET button/power-up

  reg [3:0] d; // non-inverted data for aled

  // tmr_clk is ~ 5Hz
  defparam I1.TIMER_DIV = "1048576";
  OSCTIMER I1 (.DYNOSCDIS(1'b0), .TIMERRES(1'b0), .OSCOUT(osc_clk), .TIMEROUT(tmr_clk));

  // our FLIP LEDs untouched
  assign led[0] = nrst;
  assign led[1] = !led[0];

  // animated led use inverted signal - D
  assign aled = ~ d;

  // use positive RESET in equations
  assign rst = ~ nrst;

  always @(posedge tmr_clk or posedge rst)
     begin
	if (rst)
            d = 4'b0001; // Asynchronous processing of "rst"
         else
            d = {d[2:0],d[3]}; // Synchronous processing on posedge of "tmr_clk"
     end

endmodule

• do not forget to save it -> Ctrl-S
• in process Window double-click on Constraint Editor
• expand/double-click on res_test -> Output Pins -> aled(3:0) @ -> aled_0_
• assign 61 to aled_0_
• similarly assign:
  • Pin 60 to aled_1_
  • Pin 59 to aled_2_
  • Pin 58 to aled_3_
• press Ctrl-S to save changes
• in process window right-click on Fit Design and click on Start
• after successful compilation reprogram you Kit in ispVM

After reprogram you should see that:

• LED D5 through D8 have animated light from right to left
• LED D1, D2 have retained their original functions (D1 off, D2 on)

When RESET is pressed and hold:

• animation is stopped on initial value - only LED5 i on
• LED D1 is on, D2 is off

After RESET release (or after Power Up), only LED D2 is on and LED D5-D8 are animated.

NOTE:

Verilog HDL is quite often counterintuitive: If you think that "posedge rst" means that "rst" is processed on rising edge than you are wrong.

According to BhaskerVerilog page 78, it behaves as following:

1. all if (...) on posedge or negedge input parameters are processed asynchronously
2. implicit parameter (processed with else is processed synchronously.

So in our example: "rst" - processed asynchronously "tmr_clk" - processed synchronously on rising edge of "tmr_clk"

Hmm - now you know why "C" of "CPLD" really means "Complex" :-)

TODO

Fix simulation...

Resources