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// See LICENSE for license details.
package chisel3.util
import chisel3._
import chisel3.internal.naming.chiselName // can't use chisel3_ version because of compile order
/** Used to generate an inline (logic directly in the containing Module, no internal Module is created)
* hardware counter.
*
* Typically instantiated with apply methods in [[Counter$ object Counter]]
*
* Does not create a new Chisel Module
*
* @example {{{
* val countOn = true.B // increment counter every clock cycle
* val (counterValue, counterWrap) = Counter(countOn, 4)
* when (counterValue === 3.U) {
* ...
* }
* }}}
*
* @param n number of counts before the counter resets (or one more than the
* maximum output value of the counter), need not be a power of two
*/
@chiselName
class Counter(val n: Int) {
require(n >= 0)
val value = if (n > 1) RegInit(0.U(log2Ceil(n).W)) else 0.U
/** Increment the counter, returning whether the counter currently is at the
* maximum and will wrap. The incremented value is registered and will be
* visible on the next cycle.
*/
def inc(): Bool = {
if (n > 1) {
val wrap = value === (n-1).asUInt
value := value + 1.U
if (!isPow2(n)) {
when (wrap) { value := 0.U }
}
wrap
} else {
true.B
}
}
}
object Counter
{
/** Instantiate a [[Counter! counter]] with the specified number of counts.
*/
def apply(n: Int): Counter = new Counter(n)
/** Instantiate a [[Counter! counter]] with the specified number of counts and a gate.
*
* @param cond condition that controls whether the counter increments this cycle
* @param n number of counts before the counter resets
* @return tuple of the counter value and whether the counter will wrap (the value is at
* maximum and the condition is true).
*/
@chiselName
def apply(cond: Bool, n: Int): (UInt, Bool) = {
val c = new Counter(n)
// Note this use of var is generally frowned upon! Don't use this as an example.
// This is done because we wanted the hardware generated by c.inc() to be wrapped
// in a when statement, but still needed to refer to the final value returned by
// c.inc() so we could return cond && wrap. Unless you really, really know what
// you are doing, IGNORE THIS CODE!!!!!
var wrap: Bool = null
when (cond) { wrap = c.inc() }
(c.value, cond && wrap)
}
}
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