diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..caae82a
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,22 @@
+name: ci
+on: [pull_request, push]
+jobs:
+  codespell_and_ruff:
+    runs-on: ubuntu-24.04-arm
+    steps:
+      - uses: actions/checkout@v4
+      - uses: codespell-project/actions-codespell@v2
+        with:
+          ignore_words_list: nd
+      # - uses: astral-sh/ruff-action@v3
+
+  test_cmn_diagram:
+        runs-on: ubuntu-24.04-arm
+        steps:
+          - uses: actions/checkout@v4
+          - run: |
+              sudo src/cmn_discover.py
+              python -m json.tool ~/.cache/arm/cmn-system.json
+              echo "====="
+              src/cmn_detect_cpu.py
+              src/cmn_diagram_py
diff --git a/README.md b/README.md
index eacb8e2..f3a52c5 100644
--- a/README.md
+++ b/README.md
@@ -124,7 +124,7 @@ available through the ``perf_event_open`` interface and the ``perf``
 userspace tools. These should be sufficient for many purposes.
 
 In some cases it may be useful to construct CMN watchpoints to
-match and count certan types of interconnect traffic. This generally
+match and count certain types of interconnect traffic. This generally
 requires some level of knowledge of the CHI architecture.
 The ``cmnwatch.py`` script can be used to generate strings that
 match CHI flits. The strings can be passed to the ``perf`` command.
diff --git a/src/cmn_base.py b/src/cmn_base.py
index 1c9030d..3791ab8 100755
--- a/src/cmn_base.py
+++ b/src/cmn_base.py
@@ -9,7 +9,7 @@
 This module provides classes to model the structure of one or
 more CMN mesh interconnects. Each mesh consists of a rectangular
 grid of crosspoints (XPs), to which are attached devices such
-as requestors and home nodes.
+as requesters and home nodes.
 
 The classes (System, CMN, CMNNode and CPU) can be used directly,
 or subclassed to provide more detailed functionality.
diff --git a/src/cmn_detect_cpu.py b/src/cmn_detect_cpu.py
index 046f55e..8d40b7c 100755
--- a/src/cmn_detect_cpu.py
+++ b/src/cmn_detect_cpu.py
@@ -285,7 +285,7 @@ def prepare_system(S):
     if o_verbose:
         print("%u CPUs, %u RN-F ports" % (S.n_cpu, len(S.rnf_ports)))
     # We usually see a consistent number of CPUs per RN-F port, but not always
-    if (S.n_cpu % len(S.rnf_ports)) != 0:
+    if S.rnf_ports and (S.n_cpu % len(S.rnf_ports)) != 0:
         """
         A homogeneous system would have perhaps 1 or 2 CPUs per RN-F.
         If the number does not divide equally, it could indicate that:
diff --git a/src/cmn_devmem.py b/src/cmn_devmem.py
index 529acbe..762c584 100755
--- a/src/cmn_devmem.py
+++ b/src/cmn_devmem.py
@@ -469,7 +469,7 @@ def port_base_id(self, rP):
     def dtc_domain(self):
         """
         Return the DTC domain number of this XP, if known.
-        TBD: Recent CMN allows an XP to have multiple DTMs, with a corrresponding
+        TBD: Recent CMN allows an XP to have multiple DTMs, with a corresponding
         dtm_unit_info register for each one - implying an XP's DTMs could be in
         different domains. We have not observed this.
         """
@@ -511,7 +511,7 @@ def dtm_is_enabled(self):
         """
         e = self.test64(CMN_DTM_CONTROL, CMN_DTM_CONTROL_DTM_ENABLE)
         if self._dtm_is_enabled is not None:
-            assert e == self._dtm_is_enabled, "%s: cached DTM emable state out of sync" % self
+            assert e == self._dtm_is_enabled, "%s: cached DTM enable state out of sync" % self
         return e
 
     def dtm_clear_fifo(self):
diff --git a/src/cmn_flits.py b/src/cmn_flits.py
index d758c69..8f5b172 100644
--- a/src/cmn_flits.py
+++ b/src/cmn_flits.py
@@ -305,7 +305,7 @@ def long_str(self):
                     else:
                         # SnpDVMOp part 1: often address[:6], but sometimes low
                         # bits are used for other purposes e.g. IS, TTL, TG
-                        # Wthout seeing part 0, our heuristic is that if any bits
+                        # Without seeing part 0, our heuristic is that if any bits
                         # from bit 7 on are set, it's an address.
                         if (addr >> 7) != 0:
                             address = (addr >> 1) << 6
diff --git a/src/cmnwatch.py b/src/cmnwatch.py
index 95cbbc6..0c3e23e 100755
--- a/src/cmnwatch.py
+++ b/src/cmnwatch.py
@@ -325,7 +325,7 @@ def _object_to_dict(obj, fields):
    CMN-650: 7.1, tables 7-1 on
    CMN-700: 6.1, tables 6-1 on
 
-Some fields may exist in multple match groups, while others only exist
+Some fields may exist in multiple match groups, while others only exist
 in one. This gives us some flexibility in how we allocate fields.
 
 CMN-650, CMN-700 and CI-700 appear to be the same.
@@ -341,7 +341,7 @@ def _object_to_dict(obj, fields):
     "srcid":      (None,   [(0, 0, 11)],  [(0, 0, 11), (2, 0, 11)]),
     "tgtid":      (None,   [(0, 0, 11)],  [(0, 0, 11), (2, 0, 11)]),
     "returnnid":  (None,   [(0, 11, 11)], [(0, 11, 11)]),
-    "endian":     (None,   [(0, 22, 1)],  [(0, 22, 1)]),     # overlays wth stashnidvalid/deep
+    "endian":     (None,   [(0, 22, 1)],  [(0, 22, 1)]),     # overlays with stashnidvalid/deep
     "opcode":     (chi_spec.opcodes_REQ, [(0, 31, 6)],  [(0, 29, 7), (2, 11, 7)]),
     "size":       (None,   [(0, 37, 3)],  [(0, 36, 3)]),
     "ns":         (chi_spec.NS,   [(0, 40, 1)],  [(0, 39, 1)]),