add example pipeline.py

diff --git a/pipestage.py b/pipestage.py
new file mode 100644 (file)
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+++ b/pipestage.py
@@ -0,0 +1,88 @@
+""" Example 5: Making use of PyRTL and Introspection. """
+
+from copy import deepcopy
+from migen import *
+from migen.fhdl import verilog
+
+
+# The following example shows how pyrtl can be used to make some interesting
+# hardware structures using python introspection.  In particular, this example
+# makes a N-stage pipeline structure.  Any specific pipeline is then a derived
+# class of SimplePipeline where methods with names starting with "stage" are
+# stages, and new members with names not starting with "_" are to be registered
+# for the next stage.
+
+class SimplePipeline(object):
+    """ Pipeline builder with auto generation of pipeline registers. """
+
+    def __init__(self, pipe):
+        self._pipe = pipe
+        self._pipeline_register_map = {}
+        self._current_stage_num = 0
+
+    def _setup(self):
+        stage_list = [method for method in dir(self) if method.startswith('stage')]
+        for stage in sorted(stage_list):
+            stage_method = getattr(self, stage)
+            stage_method()
+            self._current_stage_num += 1
+
+    def __getattr__(self, name):
+        try:
+            return self._pipeline_register_map[self._current_stage_num][name]
+        except KeyError:
+            raise AttributeError(
+                'error, no pipeline register "%s" defined for stage %d'
+                % (name, self._current_stage_num))
+
+    def __setattr__(self, name, value):
+        if name.startswith('_'):
+            # do not do anything tricky with variables starting with '_'
+            object.__setattr__(self, name, value)
+        else:
+            next_stage = self._current_stage_num + 1
+            pipereg_id = str(self._current_stage_num) + 'to' + str(next_stage)
+            rname = 'pipereg_' + pipereg_id + '_' + name
+            #new_pipereg = pyrtl.Register(bitwidth=len(value), name=rname)
+            new_pipereg = Signal(len(value), name_override=rname)
+            if next_stage not in self._pipeline_register_map:
+                self._pipeline_register_map[next_stage] = {}
+            self._pipeline_register_map[next_stage][name] = new_pipereg
+            self._pipe.sync += new_pipereg.eq(value)
+
+
+class SimplePipelineExample(SimplePipeline):
+    """ A very simple pipeline to show how registers are inferred. """
+
+    def __init__(self, pipe):
+        super(SimplePipelineExample, self).__init__(pipe)
+        self._loopback = Signal()
+        self._setup()
+
+    def stage0(self):
+        n = Signal()
+        self.n = ~self._loopback
+
+    def stage1(self):
+        self.n = self.n
+
+    def stage2(self):
+        self.n = self.n
+
+    def stage3(self):
+        self.n = self.n
+
+    def stage4(self):
+        self._pipe.sync += self._loopback.eq(self.n)
+
+class PipeModule(Module):
+    def __init__(self):
+        Module.__init__(self)
+
+if __name__ == "__main__":
+    example = PipeModule()
+    pipe = SimplePipelineExample(example)
+    print(verilog.convert(example,
+         { 
+           pipe._loopback,
+         }))