1
0
rocket-chip/rocket/src/main/scala/ecc.scala
2013-08-12 10:39:11 -07:00

147 lines
3.5 KiB
Scala

package rocket
import Chisel._
import uncore._
import Util._
abstract class Decoding
{
def uncorrected: Bits
def corrected: Bits
def correctable: Bool
def uncorrectable: Bool
def error = correctable || uncorrectable
}
abstract class Code
{
def width(w0: Int): Int
def encode(x: Bits): Bits
def decode(x: Bits): Decoding
}
class IdentityCode extends Code
{
def width(w0: Int) = w0
def encode(x: Bits) = x
def decode(y: Bits) = new Decoding {
def uncorrected = y
def corrected = y
def correctable = Bool(false)
def uncorrectable = Bool(false)
}
}
class ParityCode extends Code
{
def width(w0: Int) = w0+1
def encode(x: Bits) = Cat(x.xorR, x)
def decode(y: Bits) = new Decoding {
def uncorrected = y(y.getWidth-2,0)
def corrected = uncorrected
def correctable = Bool(false)
def uncorrectable = y.xorR
}
}
class SECCode extends Code
{
def width(k: Int) = {
val m = log2Up(k) + 1 - !isPow2(k)
k + m + ((1 << m) < m+k+1)
}
def encode(x: Bits) = {
val k = x.getWidth
require(k > 0)
val n = width(k)
val y = for (i <- 1 to n) yield {
if (isPow2(i)) {
val r = for (j <- 1 to n; if j != i && (j & i))
yield x(mapping(j))
r reduce (_^_)
} else
x(mapping(i))
}
Vec(y).toBits
}
def decode(y: Bits) = new Decoding {
val n = y.getWidth
require(n > 0 && !isPow2(n))
val p2 = for (i <- 0 until log2Up(n)) yield 1 << i
val syndrome = p2 map { i =>
val r = for (j <- 1 to n; if j & i)
yield y(j-1)
r reduce (_^_)
}
val s = Vec(syndrome).toBits
private def swizzle(z: Bits) = Vec((1 to n).filter(i => !isPow2(i)).map(i => z(i-1))).toBits
def uncorrected = swizzle(y)
def corrected = swizzle(((y.toUInt << 1) ^ UIntToOH(s)) >> 1)
def correctable = s.orR
def uncorrectable = Bool(false)
}
private def mapping(i: Int) = i-1-log2Up(i)
}
class SECDEDCode extends Code
{
private val sec = new SECCode
private val par = new ParityCode
def width(k: Int) = sec.width(k)+1
def encode(x: Bits) = par.encode(sec.encode(x))
def decode(x: Bits) = new Decoding {
val secdec = sec.decode(x(x.getWidth-2,0))
val pardec = par.decode(x)
def uncorrected = secdec.uncorrected
def corrected = secdec.corrected
def correctable = pardec.uncorrectable
def uncorrectable = !pardec.uncorrectable && secdec.correctable
}
}
object ErrGen
{
// generate a 1-bit error with approximate probability 2^-f
def apply(width: Int, f: Int): Bits = {
require(width > 0 && f >= 0 && log2Up(width) + f <= 16)
UIntToOH(LFSR16()(log2Up(width)+f-1,0))(width-1,0)
}
def apply(x: Bits, f: Int): Bits = x ^ apply(x.getWidth, f)
}
class SECDEDTest extends Module
{
val code = new SECDEDCode
val k = 4
val n = code.width(k)
val io = new Bundle {
val original = Bits(OUTPUT, k)
val encoded = Bits(OUTPUT, n)
val injected = Bits(OUTPUT, n)
val uncorrected = Bits(OUTPUT, k)
val corrected = Bits(OUTPUT, k)
val correctable = Bool(OUTPUT)
val uncorrectable = Bool(OUTPUT)
}
val c = Counter(Bool(true), 1 << k)
val numErrors = Counter(c._2, 3)._1
val e = code.encode(c._1)
val i = e ^ Mux(numErrors < 1, 0, ErrGen(n, 1)) ^ Mux(numErrors < 2, 0, ErrGen(n, 1))
val d = code.decode(i)
io.original := c._1
io.encoded := e
io.injected := i
io.uncorrected := d.uncorrected
io.corrected := d.corrected
io.correctable := d.correctable
io.uncorrectable := d.uncorrectable
}