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正弦 ROM

让我们假设您想要生成一个正弦波，并且还有它的滤波版本（这在实际中完全没用，但让我们以此为例）。

参数名称	类型	描述
resolutionWidth	Int	用于表示数值的位宽
sampleCount	Int	一个正弦周期内的采样点数

IO名称	方向	类型	描述
sin	out	SInt(resolutionWidth bits)	作为正弦波的输出
sinFiltered	out	SInt(resolutionWidth bits)	作为滤波后正弦波的输出

那么让我们定义一个 Component ：

case class SineRom(resolutionWidth: Int, sampleCount: Int) extends Component {
  val io = new Bundle {
    val sin = out SInt(resolutionWidth bits)
    val sinFiltered = out SInt(resolutionWidth bits)
  }
...

为了在 sin 输出端口上输出正弦波，您可以定义一个 ROM，其包含正弦波一个周期内所有采样点（可能只是四分之一，但让我们以最简单的方式做事）。然后你可以用相位计数器读取该ROM，这将生成你的正弦波。

  // Calculate values for the lookup table
  def sinTable = for(sampleIndex <- 0 until sampleCount) yield {
    val sinValue = Math.sin(2 * Math.PI * sampleIndex / sampleCount)
    S((sinValue * ((1<<resolutionWidth)/2-1)).toInt,resolutionWidth bits)
  }

  val rom =  Mem(SInt(resolutionWidth bits),initialContent = sinTable)
  val phase = Reg(UInt(log2Up(sampleCount) bits)) init 0
  phase := phase + 1

  io.sin := rom.readSync(phase)

随后生成 sinFiltered ，例如您可以使用一个一阶低通滤波器：

  io.sinFiltered := RegNext(io.sinFiltered  - (io.sinFiltered  >> 5) + (io.sin >> 5)) init 0

这是完整的代码：

case class SineRom(resolutionWidth: Int, sampleCount: Int) extends Component {
  val io = new Bundle {
    val sin = out SInt(resolutionWidth bits)
    val sinFiltered = out SInt(resolutionWidth bits)
  }

  // Calculate values for the lookup table
  def sinTable = for(sampleIndex <- 0 until sampleCount) yield {
    val sinValue = Math.sin(2 * Math.PI * sampleIndex / sampleCount)
    S((sinValue * ((1<<resolutionWidth)/2-1)).toInt,resolutionWidth bits)
  }

  val rom =  Mem(SInt(resolutionWidth bits),initialContent = sinTable)
  val phase = Reg(UInt(log2Up(sampleCount) bits)) init 0
  phase := phase + 1

  io.sin := rom.readSync(phase)

  io.sinFiltered := RegNext(io.sinFiltered  - (io.sinFiltered  >> 5) + (io.sin >> 5)) init 0
}