Periodically check if WaveDrom is loaded before calling

`WaveDrom.ProcessAll()`, rather than calling it `onload`. This fixes an issue
where traces may not render when first executing a `render_trace()` cell,
because it races with loading the JavaScript libraries.

Author: fdxmw

pyrtl/simulation.py

@@ -1763,23 +1763,31 @@ def render_trace(
         if _currently_in_jupyter_notebook():
             from IPython.display import (
                 HTML,
+                Javascript,
                 display,
             )
 
             from pyrtl.visualization import trace_to_html
 
-            htmlstring = trace_to_html(
-                self, trace_list=trace_list, sortkey=_trace_sort_key
+            display(
+                HTML(
+                    trace_to_html(self, trace_list=trace_list, sortkey=_trace_sort_key)
+                ),
+                HTML("""
+                <script src="https://cdnjs.cloudflare.com/ajax/libs/wavedrom/1.6.2/skins/default.js"></script>
+                <script src="https://cdnjs.cloudflare.com/ajax/libs/wavedrom/1.6.2/wavedrom.min.js"></script>
+                """),
+                # Wait for WaveDrom to load, polling every 100ms.
+                Javascript("""
+                var interval = setInterval(function() {
+                    if (typeof WaveDrom !== 'undefined' &&
+                        typeof WaveDrom.ProcessAll === 'function') {
+                        clearInterval(interval);
+                        WaveDrom.ProcessAll();
+                    }
+                }, 100);
+                """),
             )
-            html_elem = HTML(htmlstring)
-            display(html_elem)
-            # print(htmlstring)
-            html_stuff = """
-            <script src="https://cdnjs.cloudflare.com/ajax/libs/wavedrom/1.6.2/skins/default.js"></script>
-            <script src="https://cdnjs.cloudflare.com/ajax/libs/wavedrom/1.6.2/wavedrom.min.js"></script>
-            <style onload="WaveDrom.ProcessAll();"></style>
-            """
-            display(HTML(html_stuff))
         else:
             self.render_trace_to_text(
                 trace_list=trace_list,