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Fix Decodetable #3563

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merged 3 commits into from
Oct 16, 2023
Merged

Fix Decodetable #3563

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8ac468a
bug fix for decoderbundle not being able to be lhs op
sequencer Oct 2, 2023
a4be6d5
add default field for DecodeField for DecodeTable non X case
sequencer Oct 2, 2023
334172d
add test to show DecodeField default use case
sequencer Oct 16, 2023
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20 changes: 12 additions & 8 deletions src/main/scala/chisel3/util/experimental/decode/DecoderBundle.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -23,11 +23,15 @@ trait DecodeField[T <: DecodePattern, D <: Data] {

def chiselType: D

def default: BitPat = dc

final def width: Int = chiselType.getWidth

def dc: BitPat = BitPat.dontCare(width)

def genTable(op: T): BitPat

require(width == default.width)
}

/**
Expand All @@ -47,9 +51,9 @@ trait BoolDecodeField[T <: DecodePattern] extends DecodeField[T, Bool] {
* Output of DecoderTable
* @param fields all fields to be decoded
*/
class DecodeBundle(fields: Seq[DecodeField[_, _]]) extends Record {
class DecodeBundle(fields: Seq[DecodeField[_, _ <: Data]]) extends Record {
require(fields.map(_.name).distinct.size == fields.size, "Field names must be unique")
val elements: SeqMap[String, Data] = SeqMap(fields.map(k => k.name -> UInt(k.width.W)): _*)
val elements: SeqMap[String, Data] = SeqMap(fields.map(k => k.name -> k.chiselType): _*)

/**
* Get result of each field in decoding result
Expand All @@ -58,7 +62,7 @@ class DecodeBundle(fields: Seq[DecodeField[_, _]]) extends Record {
* @tparam D type of field
* @return hardware value of decoded output
*/
def apply[D <: Data](field: DecodeField[_, D]): D = elements(field.name).asTypeOf(field.chiselType)
def apply[D <: Data](field: DecodeField[_, D]): D = elements(field.name).asInstanceOf[D]
}

/**
Expand All @@ -71,15 +75,15 @@ class DecodeBundle(fields: Seq[DecodeField[_, _]]) extends Record {
* @param fields all fields as decoded output
* @tparam I concrete type of input patterns trait
*/
class DecodeTable[I <: DecodePattern](patterns: Seq[I], fields: Seq[DecodeField[I, _]]) {
class DecodeTable[I <: DecodePattern](patterns: Seq[I], fields: Seq[DecodeField[I, _ <: Data]]) {
require(patterns.map(_.bitPat.getWidth).distinct.size == 1, "All instructions must have the same width")

def bundle: DecodeBundle = new DecodeBundle(fields)

private val _table = patterns.map { op =>
op.bitPat -> fields.reverse.map(field => field.genTable(op)).reduce(_ ## _)
}
val table: TruthTable = TruthTable(_table, BitPat.dontCare(_table.head._2.getWidth))
val table: TruthTable = TruthTable(
patterns.map { op => op.bitPat -> fields.reverse.map(field => field.genTable(op)).reduce(_ ## _) },
fields.reverse.map(_.default).reduce(_ ## _)
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I don't understand this part of the change, this feels very different than the previous use of BitPat.dontCare.

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because some time we don't use don't care as our default selection(e.g. illinstr will default be false), thus I added a default field to let user choose their own default.

)

def decode(input: UInt): DecodeBundle = chisel3.util.experimental.decode.decoder(input, table).asTypeOf(bundle)
}
13 changes: 12 additions & 1 deletion src/test/scala/chiselTests/util/experimental/DecoderTableSpec.scala
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Expand Up @@ -42,10 +42,20 @@ class DecoderTableSpec extends ChiselFlatSpec {
}
}

object legal extends BoolDecodeField[Insn] {
override def name = "legal"

// default decode to n rather than don't care, for some special elements
override def default: BitPat = n

override def genTable(i: Insn): BitPat = y
}

class ExampleALUDecoder extends Module {
val inst = IO(Input(UInt(4.W)))
val isWideOp = IO(Output(Bool()))
val isAddOp = IO(Output(Bool()))
val isLegal = IO(Output(Bool()))

val allInstructions = Seq(
Insn(Op.add, true),
Expand All @@ -54,10 +64,11 @@ class DecoderTableSpec extends ChiselFlatSpec {
Insn(Op.sub, false)
)

val decodeTable = new DecodeTable(allInstructions, Seq(IsWideOp, IsAddOp))
val decodeTable = new DecodeTable(allInstructions, Seq(IsWideOp, IsAddOp, legal))
val decodedBundle = decodeTable.decode(inst)
isWideOp := decodedBundle(IsWideOp)
isAddOp := decodedBundle(IsAddOp)
isLegal := decodedBundle(legal)
}

"DecoderTable" should "elaborate a decoder" in {
Expand Down