add slots demo

examples/src/main/scala/spinaldoc/examples/advanced/Slots.scala

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+package spinaldoc.examples.advanced
+
+import spinal.core._
+import spinal.lib._
+import scala.language.postfixOps
+
+case class SlotsDemo(slotsCount : Int) extends Component {
+  //...
+
+
+  //Create the hardware for each slot
+  //Note each slot is an Area, not a Bundle
+  val slots = for(i <- 0 until slotsCount) yield new Area{
+    //Because the slot is an Area, we can define mix signal, registers, logic definitions
+    //Here are the registers for each slots
+    val valid = RegInit(False)
+    val address = Reg(UInt(8 bits))
+    val age = Reg(UInt(16 bits)) //Will count since how many cycles the slot is valid
+
+    //Here is some hardware behaviour for each slots
+    //Implement the age logic
+    when(valid){
+      age := age + 1
+    }
+
+    //removeIt will be used as a slot interface later on
+    val removeIt = False
+    when(removeIt){
+      valid := False
+    }
+  }
+
+  //Logic to allocate a new slot
+  val insert = new Area{
+    val cmd = Stream(UInt(8 bits)) //interface to issue requests
+    val free = slots.map(!_.valid)
+    val freeOh = OHMasking.first(free) //Get the first free slot (on hot mask)
+    cmd.ready := free.orR //Only allow cmd when there is a free slot
+    when(cmd.fire){
+      //slots.onMask(freeOh)(code) will execute the code for each slot where the corresponding freeOh bit is set
+      slots.onMask(freeOh){slot =>
+        slot.valid := True
+        slot.address := cmd.payload
+        slot.age := 0
+      }
+    }
+  }
+
+  //Logic to remove the slots which match a given address (assuming there is not more than one match)
+  val remove = new Area{
+    val cmd = Flow(UInt(8 bits))//interface to issue requests
+    val oh = slots.map(s => s.valid && s.address === cmd.payload) //oh meaning "one hot"
+    when(cmd.fire){
+      slots.onMask(oh){ slot =>
+        slot.removeIt := True
+      }
+    }
+
+    val reader = slots.reader(oh) //Create a facility to read the slots using "oh" as index
+    val age = reader(_.age) //Age of the slot which is selected by "oh"
+  }
+
+  //...
+}
+
+object SlotsDemo extends App {
+  SpinalVerilog(SlotsDemo(4))
+}

source/SpinalHDL/Examples/Advanced ones/slots.rst

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+.. _Slots:
+
+Slots
+=====
+
+Introduction
+------------
+
+Let's say you have some hardware which has to keep track of multiple similar ongoing activities, you may want to implement an array of "slots" to do so. This example show how to do it using Area, OHMasking.first, onMask and reader.
+
+
+Implementation
+^^^^^^^^^^^^^^
+
+This implementation avoid the use of Vec. Instead, it use Area which allow to mix signal, registers and logic definitions in each slot.
+
+.. literalinclude:: /../examples/src/main/scala/spinaldoc/examples/advanced/Timer.scala
+   :language: scala
+
+