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. 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=encodingOfYouChoice) {
val element0, element1, ..., elementN = newElement()
}
Encoding
The following enumeration encodings are supported :
| Encoding | Bit width | Description |
|---|---|---|
| native | - | Use the VHDL enumeration system, this is the default encoding |
| binarySequancial | 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 correspond to one state |
Custom encoding can be performed in two different ways: static or dynamic.
/*
* Static encoding
*/
object MyEnumStatic extends SpinalEnum{
val e0, e1, e2, e3 = new Element()
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 = new Element()
}
Example
Instantiate a 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 the visibility on 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 in Bits | Bits(w(x) bits) |
| x.asUInt | Binary cast in UInt | UInt(w(x) bits) |
| x.asSInt | Binary cast in SInt | SInt(w(x) bits) |
import UartCtrlTxState._
val stateNext = UartCtrlTxState()
myBits := sIdle.asBits