Add doc about SVIF (system verilog interface)

source/SpinalHDL/Data types/SVIF.rst

@@ -0,0 +1,171 @@
+.. _SVIF:
+
+SVIF
+======
+
+Description
+^^^^^^^^^^^
+
+The ``SVIF`` type specifically targets system Verilog designs.This type extends from ``Bundle``.When generating Verilog or VHDL, the behavior of this type is exactly the same as that of ``Bundle``.However, when generating System Verilog and enabling the ``svInterface`` option in SpinalConfig, this type will be generated as an Interface.
+
+This type is still an experimental feature
+
+Declaration
+^^^^^^^^^^^
+
+The syntax to declare a SVIF is as follows:
+
+.. code-block:: scala
+
+   case class myBundle extends SVIF {
+     val bundleItem0 = AnyType
+     val bundleItem1 = AnyType
+     val bundleItemN = AnyType
+   }
+
+For example, a SVIF holding a color could be defined as:
+
+.. code-block:: scala
+
+   case class Color(channelWidth: Int) extends SVIF {
+     val r, g, b = UInt(channelWidth bits)
+   }
+
+modport
+~~~~~~~
+
+``modport`` can be implemented through add annotations above functions, with the function name serving as the modport name.
+
+.. code-block:: scala
+
+   case class Color(channelWidth: Int) extends SVIF {
+     val r, g, b = UInt(channelWidth bits)
+
+     @modport
+     def mst = {
+        out(r, g, b)
+     }
+
+     @modport
+     def slv = {
+        in(r, g, b)
+     }
+   }
+
+with ``IMasterSlave``：
+
+.. code-block:: scala
+
+   case class Color(channelWidth: Int) extends SVIF with IMasterSlave {
+     val r, g, b = UInt(channelWidth bits)
+
+     override def asMaster = {
+        out(r, g, b)
+     }
+
+     @modport
+     def mst = asMaster
+
+     @modport
+     def slv = asSlave
+   }
+
+Parameter
+~~~~~~~~~
+
+.. code-block:: scala
+
+   case class Color(channelWidth: Int) extends SVIF {
+     val width = addGeneric("WIDTH", channelWidth)// or addParameter
+     val r, g, b = UInt(channelWidth bits)
+     tieGeneric(r, width)// or tieParameter
+     tieGeneric(g, width)
+     tieGeneric(b, width)
+
+     @modport
+     def mst = out(r, g, b)
+
+     @modport
+     def slv = in(r, g, b)
+   }
+
+.. code-block:: scala
+
+   case class ColorHandShake(Width: Int) extends SVIF with IMasterSlave {
+     val w = addGeneric("W", Width, default = "8")
+     val valid = Bool()
+     val payload = Color(Width)
+     val ready = Bool()
+     tieIFParameter(payload, "WIDTH", "W") // for generate "  .WIDTH (W)"
+
+     override def asMaster = {
+       out(valid, payload)
+       in(ready)
+     }
+
+     @modport
+     def mst = asMaster
+
+     @modport
+     def slv = asSlave
+   }
+
+this will generate system verilog code as below:
+
+.. code-block:: scala
+
+   interface ColorHandShake #(
+      parameter W = 8
+   ) () ;
+
+      logic           valid ;
+      Color #(
+         .WIDTH (W)
+      ) payload();
+      logic           ready ;
+
+      modport mst (
+         output          valid,
+         Color.slv       payload,
+         input           ready
+      );
+
+      modport slv (
+         input           valid,
+         Color.mst       payload,
+         output          ready
+      );
+
+   endinterface
+
+   interface Color #(
+      parameter WIDTH
+   ) () ;
+
+      logic  [WIDTH-1:0] r ;
+      logic  [WIDTH-1:0] g ;
+      logic  [WIDTH-1:0] b ;
+
+      modport mst (
+         input           r,
+         input           g,
+         input           b
+      );
+
+      modport slv (
+         output          r,
+         output          g,
+         output          b
+      );
+
+   endinterface
+
+Definition Name
+~~~~~~~~~~~~~~~
+
+you can use ``setDefinitionName`` to set the definition name. But remember to use it before any clone of this interface
+
+Not Interface
+~~~~~~~~~~~~~
+
+If you have used a certain interface in multiple places, and at one of those locations ``sigA``, you wish to flatten it instead of generating an interface, you can achieve this by calling ``sigA.notSVIF()`` to fully flatten the signal. If the signal has nested interfaces and you only want to expand the outermost layer, you can use ``sigA.notSVIFthisLevel()``.