M_CPU/SRAM placement via pos_mm in topology.yaml (nearest router)

Component placement uses mm coordinates in topology.yaml, mesh_gen
finds the nearest router automatically. M_CPU moved to pos_mm=[7.5,2.0]
(→ r0c2), SRAM at pos_mm=[1.5,9.0] (→ r3c0).

No hardcoded router references in topology config.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/diagrams/cube_view.svg

@@ -141,8 +141,11 @@
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   <text x="435" y="138" text-anchor="middle" font-family="monospace" font-size="6" fill="white">r0c2</text>
+  <rect x="419" y="81" width="32" height="16" rx="3" fill="#451a03" stroke="#f59e0b" stroke-width="1"/>
+  <text x="435" y="92" text-anchor="middle" font-family="monospace" font-size="7" font-weight="bold" fill="#f59e0b">M_CPU</text>
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@@ -167,11 +170,8 @@
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src/kernbench/topology/mesh_gen.py

@@ -53,6 +53,7 @@ def _compute_source_hash(cube_spec: dict) -> str:
         "hbm_mapping_mode": cube_spec.get("memory_map", {}).get(
             "hbm_mapping_mode", "n_to_one"
         ),
+        "placement": cube_spec.get("placement", {}),
     }
     raw = yaml.dump(relevant, sort_keys=True)
     return hashlib.sha256(raw.encode()).hexdigest()[:16]
@@ -221,13 +222,29 @@ def _generate_mesh(cube_spec: dict, source_hash: str) -> dict:
 
             pe_idx += 1
 
-    # M_CPU and SRAM attachments (HBM row, leftmost available)
+    # M_CPU and SRAM attachments: find nearest router to configured position
-    mcpu_key = f"r{hbm_row_start}c0"
+    placement = cube_spec.get("placement", {})
-    if routers.get(mcpu_key) is not None:
+
+    def _nearest_router(target_mm: list[float]) -> str | None:
+        best_key, best_dist = None, float("inf")
+        for rk, rv in routers.items():
+            if rv is None:
+                continue
+            rx, ry = rv["pos_mm"]
+            dist = math.sqrt((rx - target_mm[0]) ** 2 + (ry - target_mm[1]) ** 2)
+            if dist < best_dist:
+                best_dist = dist
+                best_key = rk
+        return best_key
+
+    mcpu_pos = placement.get("m_cpu", {}).get("pos_mm", [1.5, 5.5])
+    mcpu_key = _nearest_router(mcpu_pos)
+    if mcpu_key and routers.get(mcpu_key) is not None:
         routers[mcpu_key]["attach"].append("m_cpu")
 
-    sram_key = f"r{hbm_row_end}c0"
+    sram_pos = placement.get("sram", {}).get("pos_mm", [1.5, 8.5])
-    if routers.get(sram_key) is not None:
+    sram_key = _nearest_router(sram_pos)
+    if sram_key and routers.get(sram_key) is not None:
         routers[sram_key]["attach"].append("sram")
 
     # UCIe PE rows: top-half rows + bottom-half rows (1 per PE row)

tests/test_topology_compile.py

@@ -158,9 +158,9 @@ def test_pe_dma_to_router():
 def test_command_path_m_cpu_router_pe_cpu():
     es = _edge_set(_graph())
     cp = "sip0.cube0"
-    # m_cpu <-> r2c0 (bidirectional command)
+    # m_cpu <-> r0c2 (bidirectional command)
-    assert (f"{cp}.m_cpu", f"{cp}.r2c0") in es
+    assert (f"{cp}.m_cpu", f"{cp}.r0c2") in es
-    assert (f"{cp}.r2c0", f"{cp}.m_cpu") in es
+    assert (f"{cp}.r0c2", f"{cp}.m_cpu") in es
     # router -> pe_cpu for each PE (command kind)
     assert (f"{cp}.r0c0", f"{cp}.pe0.pe_cpu") in es
     assert (f"{cp}.r5c5", f"{cp}.pe7.pe_cpu") in es
@@ -416,8 +416,8 @@ def test_cube_view_hbm_router():
 
 
 def test_cube_view_m_cpu_router():
-    """Cube view: m_cpu connects to its router r2c0."""
+    """Cube view: m_cpu connects to its router r0c2."""
     v = _graph().cube_view
     ves = {(e.src, e.dst) for e in v.edges}
-    assert ("m_cpu", "r2c0") in ves
+    assert ("m_cpu", "r0c2") in ves
-    assert ("r2c0", "m_cpu") in ves
+    assert ("r0c2", "m_cpu") in ves

topology.yaml

@@ -95,6 +95,11 @@ cube:
     hbm_ctrl:   { kind: hbm_ctrl, impl: hbm_ctrl_v1, attrs: { capacity: 1, efficiency: 1.0 } }
     sram:       { kind: sram,     impl: sram_v1,     attrs: { size_mb: 32, overhead_ns: 2.0 } }
 
+  # Physical placement of non-PE components (mm coordinates)
+  placement:
+    m_cpu:  { pos_mm: [7.5, 2.0] }   # top center area, near UCIe-N
+    sram:   { pos_mm: [1.5, 9.0] }   # left side, below HBM zone
+
   ucie:
     decompose: true
     ports: [N, S, E, W]