add generic error correcting codes
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128
rocket/src/main/scala/ecc.scala
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128
rocket/src/main/scala/ecc.scala
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package rocket
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import Chisel._
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import Constants._
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import uncore._
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import Util._
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abstract class Decoding
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{
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def uncorrected: Bits
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def corrected: Bits
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def correctable: Bool
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def uncorrectable: Bool
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def error = correctable || uncorrectable
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}
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abstract class Encoding
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{
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def width(w0: Int): Int
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def encode(x: Bits): Bits
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def decode(x: Bits): Decoding
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}
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class Parity extends Encoding
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{
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def width(w0: Int) = w0+1
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def encode(x: Bits) = Cat(x.xorR, x)
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def decode(y: Bits) = new Decoding {
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def uncorrected = y(y.getWidth-2,0)
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def corrected = uncorrected
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def correctable = y.xorR
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def uncorrectable = Bool(false)
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}
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}
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class SEC extends Encoding
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{
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def width(k: Int) = {
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val m = log2Up(k) + 1 - !isPow2(k)
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k + m + ((1 << m) < m+k+1)
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}
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def encode(x: Bits) = {
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val k = x.getWidth
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require(k > 0)
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val n = width(k)
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val y = for (i <- 1 to n) yield {
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if (isPow2(i)) {
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val r = for (j <- 1 to n; if j != i && (j & i))
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yield x(mapping(j))
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r reduce (_^_)
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} else
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x(mapping(i))
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}
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Vec(y){Bool()}.toBits
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}
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def decode(y: Bits) = new Decoding {
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val n = y.getWidth
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require(n > 0 && !isPow2(n))
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val p2 = for (i <- 0 until log2Up(n)) yield 1 << i
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val syndrome = p2 map { i =>
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val r = for (j <- 1 to n; if j & i)
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yield y(j-1)
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r reduce (_^_)
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}
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val s = Vec(syndrome){Bool()}.toBits
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private def swizzle(z: Bits) = Vec((1 to n).filter(i => !isPow2(i)).map(i => z(i-1))){Bool()}.toBits
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def uncorrected = swizzle(y)
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def corrected = swizzle(((y << 1) ^ UFixToOH(s)) >> 1)
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def correctable = s.orR
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def uncorrectable = Bool(false)
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}
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private def mapping(i: Int) = i-1-log2Up(i)
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}
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class SECDED extends Encoding
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{
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def width(k: Int) = new SEC().width(k)+1
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def encode(x: Bits) = new Parity().encode(new SEC().encode(x))
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def decode(x: Bits) = new Decoding {
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val sec = new SEC().decode(x(x.getWidth-2,0))
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val par = new Parity().decode(x)
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def uncorrected = sec.uncorrected
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def corrected = sec.corrected
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def correctable = par.correctable
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def uncorrectable = !par.correctable && sec.correctable
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}
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}
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class SECDEDTest extends Component
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{
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def inject(x: Bits, n: UFix) = {
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val r = LFSR16()
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val r1 = UFixToOH(r(log2Up(x.getWidth)-1,0))(x.getWidth-1,0)
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val r2 = UFixToOH(r(log2Up(x.getWidth)*2-1,log2Up(x.getWidth)))(x.getWidth-1,0)
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x ^ Mux(n < UFix(1), UFix(0), r1) ^ Mux(n < UFix(2), UFix(0), r2)
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}
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val code = new SECDED
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val k = 4
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val n = code.width(k)
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val io = new Bundle {
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val original = Bits(OUTPUT, k)
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val encoded = Bits(OUTPUT, n)
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val injected = Bits(OUTPUT, n)
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val uncorrected = Bits(OUTPUT, k)
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val corrected = Bits(OUTPUT, k)
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val correctable = Bool(OUTPUT)
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val uncorrectable = Bool(OUTPUT)
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}
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val c = Counter(Bool(true), 1 << k)
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val numErrors = Counter(c._2, 3)._1
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val e = code.encode(c._1)
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val i = inject(e, numErrors)
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val d = code.decode(i)
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io.original := c._1
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io.encoded := e
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io.injected := i
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io.uncorrected := d.uncorrected
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io.corrected := d.corrected
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io.correctable := d.correctable
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io.uncorrectable := d.uncorrectable
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}
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