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SpinalEnum

Description

The Enumeration type corresponds to a list of named values.

Declaration

The declaration of an enumerated data type is as follows:

object Enumeration extends SpinalEnum {
  val element0, element1, ..., elementN = newElement()
}

For the example above, the default encoding is used. The native enumeration type is used for VHDL and a binary encoding is used for Verilog.

The enumeration encoding can be forced by defining the enumeration as follows:

object Enumeration extends SpinalEnum(defaultEncoding=encodingOfYourChoice) {
  val element0, element1, ..., elementN = newElement()
}

Note

If you want to define an enumeration as in/out for a given component, you have to do as following: in(MyEnum()) or out(MyEnum())

Encoding

The following enumeration encodings are supported:

Encoding	Bit width	Description
native		Use the VHDL enumeration system, this is the default encoding
binarySequential	log2Up(stateCount)	Use Bits to store states in declaration order (value from 0 to n-1)
binaryOneHot	stateCount	Use Bits to store state. Each bit corresponds to one state

Custom encodings can be performed in two different ways: static or dynamic.

/*
 * Static encoding
 */
object MyEnumStatic extends SpinalEnum {
  val e0, e1, e2, e3 = newElement()
  defaultEncoding = SpinalEnumEncoding("staticEncoding")(
    e0 -> 0,
    e1 -> 2,
    e2 -> 3,
    e3 -> 7)
}

/*
 * Dynamic encoding with the function :  _ * 2 + 1
 *   e.g. : e0 => 0 * 2 + 1 = 1
 *          e1 => 1 * 2 + 1 = 3
 *          e2 => 2 * 2 + 1 = 5
 *          e3 => 3 * 2 + 1 = 7
 */
val encoding = SpinalEnumEncoding("dynamicEncoding", _ * 2 + 1)

object MyEnumDynamic extends SpinalEnum(encoding) {
  val e0, e1, e2, e3 = newElement()
}

Example

Instantiate an enumerated signal and assign a value to it:

object UartCtrlTxState extends SpinalEnum {
  val sIdle, sStart, sData, sParity, sStop = newElement()
}

val stateNext = UartCtrlTxState()
stateNext := UartCtrlTxState.sIdle

// You can also import the enumeration to have visibility of its elements
import UartCtrlTxState._
stateNext := sIdle

Operators

The following operators are available for the Enumeration type:

Comparison

Operator	Description	Return type
x === y	Equality	Bool
x =/= y	Inequality	Bool

import UartCtrlTxState._

val stateNext = UartCtrlTxState()
stateNext := sIdle

when(stateNext === sStart) {
  ...
}

switch(stateNext) {
  is(sIdle) {
    ...
  }
  is(sStart) {
    ...
  }
  ...
}

Type cast

Operator	Description	Return
x.asBits	Binary cast to Bits	Bits(w(x) bits)
x.asUInt	Binary cast to UInt	UInt(w(x) bits)
x.asSInt	Binary cast to SInt	SInt(w(x) bits)

import UartCtrlTxState._

val stateNext = UartCtrlTxState()
myBits := sIdle.asBits