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// See LICENSE for license details.
package Chisel
import internal._
import internal.Builder.pushCommand
import internal.firrtl._
object Reg {
private[Chisel] def makeType[T <: Data](t: T = null, next: T = null, init: T = null): T = {
if (t ne null) {
t.cloneType
} else if (next ne null) {
next.cloneTypeWidth(Width())
} else if (init ne null) {
init.litArg match {
// For e.g. Reg(init=UInt(0, k)), fix the Reg's width to k
case Some(lit) if lit.forcedWidth => init.cloneType
case _ => init.cloneTypeWidth(Width())
}
} else {
throwException("cannot infer type")
}
}
/** Creates a register with optional next and initialization values.
*
* @param t: data type for the register
* @param next: new value register is to be updated with every cycle (or
* empty to not update unless assigned to using the := operator)
* @param init: initialization value on reset (or empty for uninitialized,
* where the register value persists across a reset)
*
* @note this may result in a type error if called from a type parameterized
* function, since the Scala compiler isn't smart enough to know that null
* is a valid value. In those cases, you can either use the outType only Reg
* constructor or pass in `null.asInstanceOf[T]`.
*/
def apply[T <: Data](t: T = null, next: T = null, init: T = null): T = {
// TODO: write this in a way that doesn't need nulls (bad Scala style),
// null.asInstanceOf[T], and two constructors. Using Option types are an
// option, but introduces cumbersome syntax (wrap everything in a Some()).
// Implicit conversions to Option (or similar) types were also considered,
// but Scala's type inferencer and implicit insertion isn't smart enough
// to resolve all use cases. If the type inferencer / implicit resolution
// system improves, this may be changed.
val x = makeType(t, next, init)
val clock = Node(x._parent.get.clock) // TODO multi-clock
if (init == null) {
pushCommand(DefReg(x, clock))
} else {
pushCommand(DefRegInit(x, clock, Node(x._parent.get.reset), init.ref))
}
if (next != null) {
x := next
}
x
}
/** Creates a register without initialization (reset is ignored). Value does
* not change unless assigned to (using the := operator).
*
* @param outType: data type for the register
*/
def apply[T <: Data](outType: T): T = Reg[T](outType, null.asInstanceOf[T], null.asInstanceOf[T])
}
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