VHDL and Verilog generation | SpinalHDL documentation

Generate VHDL and Verilog from an SpinalHDL Component

To generate the VHDL from an SpinalHDL component you just need to call SpinalVhdl(new YourComponent) in a Scala main.

To generate the Verilog, it’s exactly the same, but with SpinalVerilog in place of SpinalVHDL

import spinal.core._

//A simple component definition
class MyTopLevel extends Component {
  //Define some input/output. Bundle like a VHDL record or a verilog struct.
  val io = new Bundle {
    val a = in Bool
    val b = in Bool
    val c = out Bool
  }

  //Define some asynchronous logic
  io.c := io.a & io.b
}

//This is the main that generate the VHDL and the Verilog corresponding to MyTopLevel
object MyMain {
  def main(args: Array[String]) {
    SpinalVhdl(new MyTopLevel)
    SpinalVerilog(new MyTopLevel)
  }
}

Important: SpinalVhdl and SpinalVerilog could need to create multiple instance of your component class. It’s why its first argument is not a Component reference but a function that return a new component.

Important: SpinalVerilog implementation has start the 5 June 2016. This backend pass successfully the same regression tests than the VHDL one (RISCV CPU, Multicore and pipelined mandelbrot,UART RX/TX, Single clock fifo, Dual clock fifo, Gray counter, ..). But still, if you have any issue with this young backend, please, make a git issue.

Parametrization from Scala

Argument name	Type	Default	Description
mode	SpinalMode	null	Set the SpinalHDL mode. Could be set to `VHDL` or `Verilog`
defaultConfigForClockDomains	ClockDomainConfig	RisingEdgeClock AsynchronousReset ResetActiveHigh ClockEnableActiveHigh	Set the clock configuration that will be use as default for all new `ClockDomain`.
onlyStdLogicVectorAtTopLevelIo	Boolean	false	Change all unsigned/signed toplevel io into std_logic_vector.
defaultClockDomainFrequency	IClockDomainFrequency	UnknownFrequency	Default clock frequency
targetDirectory	String	Current directory	Directory where files are generated

And there is the syntax to specify them :

SpinalConfig(mode = VHDL, targetDirectory="temp/myDesign").generate(new UartCtrl)

// Or for Verilog in a more scalable formatting :
SpinalConfig(
  mode = Verilog,
  targetDirectory="temp/myDesign"
).generate(new UartCtrl)

Parametrization from shell

You can also specify generation parameters by using command line arguments.

def main(args: Array[String]): Unit = {
  SpinalConfig.shell(args)(new UartCtrl)
}

Arguments syntax is :

Usage: SpinalCore [options]

  --vhdl
        Select the VHDL mode
  --verilog
        Select the Verilog mode
  -d | --debug
        Enter in debug mode directly
  -o <value> | --targetDirectory <value>
        Set the target directory

Generated VHDL and Verilog

The way how a SpinalHDL RTL description is translated into VHDL and Verilog is important :

Names in Scala are preserved in VHDL and Verilog.
Component hierarchy in Scala is preserved in VHDL and Verilog.
when statements in Scala are emitted as if statements in VHDL and Verilog
switch statements in Scala are emitted as case statements in VHDL and Verilog in all standard cases

Organization

When you use the VHDL generation, stuff are generated into a single file which contain tree section :

A package that contain enumeration’s definitions
A package that contain function used by architectures
All components needed by your design

When you use the Verilog generation, stuff are generated into a single file which contain two section :

All enumeration defines
All modules needed by your design

Combinatorial logic

Scala :

class TopLevel extends Component {
  val io = new Bundle {
    val cond           = in  Bool
    val value          = in  UInt (4 bits)
    val withoutProcess = out UInt(4 bits)
    val withProcess    = out UInt(4 bits)
  }
  io.withoutProcess := io.value
  io.withProcess := 0
  when(io.cond){
    switch(io.value){
      is(U"0000"){
        io.withProcess := 8
      }
      is(U"0001"){
        io.withProcess := 9
      }
      default{
        io.withProcess := io.value+1
      }
    }
  }
}

VHDL :

entity TopLevel is
  port(
    io_cond : in std_logic;
    io_value : in unsigned(3 downto 0);
    io_withoutProcess : out unsigned(3 downto 0);
    io_withProcess : out unsigned(3 downto 0)
  );
end TopLevel;

architecture arch of TopLevel is
begin
  io_withoutProcess <= io_value;
  process(io_cond,io_value)
  begin
    io_withProcess <= pkg_unsigned("0000");
    if io_cond = '1' then
      case io_value is
        when pkg_unsigned("0000") =>
          io_withProcess <= pkg_unsigned("1000");
        when pkg_unsigned("0001") =>
          io_withProcess <= pkg_unsigned("1001");
        when others =>
          io_withProcess <= (io_value + pkg_unsigned("0001"));
      end case;
    end if;
  end process;
end arch;

Flipflop

Scala :

class TopLevel extends Component {
  val io = new Bundle {
    val cond   = in Bool
    val value  = in UInt (4 bit)
    val resultA = out UInt(4 bit)
    val resultB = out UInt(4 bit)
  }

  val regWithReset = Reg(UInt(4 bits)) init(0)
  val regWithoutReset = Reg(UInt(4 bits))

  regWithReset := io.value
  regWithoutReset := 0
  when(io.cond){
    regWithoutReset := io.value
  }

  io.resultA := regWithReset
  io.resultB := regWithoutReset
}

VHDL :

entity TopLevel is
  port(
    io_cond : in std_logic;
    io_value : in unsigned(3 downto 0);
    io_resultA : out unsigned(3 downto 0);
    io_resultB : out unsigned(3 downto 0);
    clk : in std_logic;
    reset : in std_logic
  );
end TopLevel;

architecture arch of TopLevel is

  signal regWithReset : unsigned(3 downto 0);
  signal regWithoutReset : unsigned(3 downto 0);
begin
  io_resultA <= regWithReset;
  io_resultB <= regWithoutReset;
  process(clk,reset)
  begin
    if reset = '1' then
      regWithReset <= pkg_unsigned("0000");
    elsif rising_edge(clk) then
      regWithReset <= io_value;
    end if;
  end process;

  process(clk)
  begin
    if rising_edge(clk) then
      regWithoutReset <= pkg_unsigned("0000");
      if io_cond = '1' then
        regWithoutReset <= io_value;
      end if;
    end if;
  end process;
end arch;

VHDL and Verilog attributes

In some situation, it’s useful to give some attributes to some signals of a given design to obtain a specific synthesis result.
To do that, on any signals or memory of your design you can call the following functions :

Syntax	Description
addAttribute(name)	Add a boolean attribute with the given `name` set to true
addAttribute(name,value)	Add a string attribute with the given `name` set to `value`

Example :

val pcPlus4 = pc + 4
pcPlus4.addAttribute("keep")

Produced declaration in VHDL :

attribute keep : boolean;
signal pcPlus4 : unsigned(31 downto 0);
attribute keep of pcPlus4: signal is true;

Produced declaration in Verilog :

(* keep *) wire [31:0] pcPlus4;

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