readback!

peakrdl/regblock/readback/__init__.py

@@ -1,4 +1,5 @@
 from typing import TYPE_CHECKING
+import math
 
 from .generators import ReadbackAssignmentGenerator
 from ..utils import get_always_ff_event
@@ -8,8 +9,9 @@ if TYPE_CHECKING:
     from systemrdl.node import AddrmapNode
 
 class Readback:
-    def __init__(self, exp:'RegblockExporter'):
+    def __init__(self, exp:'RegblockExporter', do_fanin_stage: bool):
         self.exp = exp
+        self.do_fanin_stage = do_fanin_stage
 
     @property
     def top_node(self) -> 'AddrmapNode':
@@ -18,13 +20,49 @@ class Readback:
     def get_implementation(self) -> str:
         gen = ReadbackAssignmentGenerator(self.exp)
         array_assignments = gen.get_content(self.top_node)
+        array_size = gen.current_offset
+
+        # Enabling the fanin stage doesnt make sense if readback fanin is
+        # small. This also avoids pesky corner cases
+        if array_size < 4:
+            self.do_fanin_stage = False
 
         context = {
             "array_assignments" : array_assignments,
-            "array_size" : gen.current_offset,
+            "array_size" : array_size,
             "get_always_ff_event": get_always_ff_event,
-            "cpuif_reset": self.exp.cpuif_reset,
+            "cpuif": self.exp.cpuif,
+            "do_fanin_stage": self.do_fanin_stage,
         }
+
+        if self.do_fanin_stage:
+            # If adding a fanin pipeline stage, goal is to try to
+            # split the fanin path in the middle so that fanin into the stage
+            # and the following are roughly balanced.
+            fanin_target = math.sqrt(array_size)
+
+            # Size of fanin group to consume per fanin element
+            fanin_stride = math.floor(fanin_target)
+
+            # Number of array elements to reduce to.
+            # Round up to an extra element in case there is some residual
+            fanin_array_size = math.ceil(array_size / fanin_stride)
+
+            # leftovers are handled in an extra array element
+            fanin_residual_stride = array_size % fanin_stride
+
+            if fanin_residual_stride != 0:
+                # If there is a partial fanin element, reduce the number of
+                # loops performed in the bulk fanin stage
+                fanin_loop_iter = fanin_array_size - 1
+            else:
+                fanin_loop_iter = fanin_array_size
+
+            context['fanin_stride'] = fanin_stride
+            context['fanin_array_size'] = fanin_array_size
+            context['fanin_residual_stride'] = fanin_residual_stride
+            context['fanin_loop_iter'] = fanin_loop_iter
+
         template = self.exp.jj_env.get_template(
             "readback/templates/readback.sv"
         )