RGB to gray
===========

Let's imagine a component that converts an RGB color into a gray one, and then writes it into external memory.

.. list-table::
   :header-rows: 1
   :widths: 1 1 2

   * - io name
     - Direction
     - Description
   * - clear
     - in
     - Clear all internal registers
   * - r,g,b
     - in
     - Color inputs
   * - wr
     - out
     - Memory write
   * - address
     - out
     - Memory address, incrementing each cycle
   * - data
     - out
     - Memory data, gray level


.. code-block:: scala

     class RgbToGray extends Component{
       val io = new Bundle{
         val clear = in Bool()
         val r,g,b = in UInt(8 bits)

         val wr = out Bool()
         val address = out UInt(16 bits)
         val data = out UInt(8 bits)
       }

       def coef(value : UInt,by : Float) : UInt = (value * U((255*by).toInt,8 bits) >> 8)
       val gray = RegNext(
         coef(io.r,0.3f) +
         coef(io.g,0.4f) +
         coef(io.b,0.3f)
       )

       val address = CounterFreeRun(stateCount = 1 << 16)
       io.address := address
       io.wr := True
       io.data := gray

       when(io.clear){
         gray := 0
         address.clear()
         io.wr := False
       }
     }