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plic: Add some assertions to check one-hot assumptions

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This commit is contained in:
Megan Wachs
2017-06-30 12:32:58 -07:00
parent 237689b799
commit 3da26b0aa8
1 changed files with 18 additions and 8 deletions
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26
src/main/scala/uncore/devices/Plic.scala
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@@ -176,12 +176,14 @@ class TLPLIC(params: PLICParams)(implicit p: Parameters) extends LazyModule
PLICConsts.enableBase(i) -> e.map(b => RegField(1, b))
}
// When a hart reads its claim/complete register, then the
// When a hart reads a claim/complete register, then the
// device which is currently its highest priority is no longer pending.
// This code expolits the fact that only one hart can claim a device at
// a time through the TL interface.
// This code expolits the fact that, practically, only one claim/complete
// register can be read at a time. We check for this because if the address map
// were to change, it may no longer be true.
// Note: PLIC doesn't care which hart reads the register.
val claimer = Wire(Vec(nHarts, Bool()))
assert((claimer.asUInt & (claimer.asUInt - UInt(1))) === UInt(0)) // One-Hot
val claiming = Vec.tabulate(nHarts){i => Mux(claimer(i), UIntToOH(maxDevs(i), nDevices+1), UInt(0))}
val claimedDevs = Vec(claiming.reduceLeft( _ | _ ).toBools)
@@ -193,12 +195,15 @@ class TLPLIC(params: PLICParams)(implicit p: Parameters) extends LazyModule
// When a hart writes a claim/complete register, then
// the written device (as long as it is actually enabled for that
// hart) is marked complete.
// This code expolits the fact that only one hart can complete a device at
// a time through the TL interface
// This code expolits the fact that, practically, only one claim/complete register
// can be written at a time. We check for this because if the address map
// were to change, it may no longer be true.
// (Note -- PLIC doesn't care which hart writes the register)
val completer = Wire(Vec(nHarts, Bool()))
val irq = data.extract(log2Ceil(nDevices+1)-1, 0)
val completedDevs = Mux(completer.reduce(_ || _), UIntToOH(irq, nDevices+1), UInt(0))
assert((completer.asUInt & (completer.asUInt - UInt(1))) === UInt(0)) // One-Hot
val completerDev = Wire(UInt(width = log2Up(nDevices + 1)))
val checkCompleterDev = Wire(Vec(nHarts, UInt(width = log2Up(nDevices + 1)))) // For assertion purposes only.
val completedDevs = Mux(completer.reduce(_ || _), UIntToOH(completerDev, nDevices+1), UInt(0))
(gateways zip completedDevs.toBools) foreach { case (g, c) =>
g.complete := c
}
@@ -212,7 +217,12 @@ class TLPLIC(params: PLICParams)(implicit p: Parameters) extends LazyModule
(Bool(true), maxDevs(i))
},
RegWriteFn { (valid, data) =>
completer(i) := valid && enables(i)(irq)
if (i > 0) {
assert(checkCompleterDev(i-1) === data.extract(log2Ceil(nDevices+1)-1, 0))
}
checkCompleterDev(i) := data.extract(log2Ceil(nDevices+1)-1, 0)
completer(i) := valid && enables(i)(completerDev)
completerDev := data.extract(log2Ceil(nDevices+1)-1, 0)
Bool(true)
}
)