Increase asyncify stack size

Pick the first power of two where we fail with a pystack exhausted
error in MicroPython rather than an asyncify-related error.

Author: microbit-matt-hillsdon

bin/stack-size.mjs

@@ -0,0 +1,33 @@
+// Generates Python files that explore stack size limits
+// We hit an asyncify limit here:
+// https://github.com/microbit-foundation/micropython-microbit-v2-simulator/issues/105
+
+// At 169 we get pystack exhausted
+// With lower powers of 2 for ASYNCIFY_STACK_SIZE we get an asyncify error
+// before we exhaust the stack.
+const limit = 168;
+
+let code = `
+def outer():
+    i = 0
+    while True:
+        print(i)
+        i += 1
+        f${limit - 1}()
+
+def f0():
+    pass
+
+`;
+
+for (let i = limit - 1; i > 0; --i) {
+  code += `
+def f${i}():
+  f${i - 1}()
+
+`;
+}
+
+code += "outer()";
+
+console.log(code);

src/Makefile

@@ -44,6 +44,8 @@ COPT += -O3 -DNDEBUG
 endif
 
 JSFLAGS += -s ASYNCIFY
+# We can hit lower values due to user stack use. See stack-size.mjs.
+JSFLAGS += -s ASYNCIFY_STACK_SIZE=262144
 JSFLAGS += -s EXIT_RUNTIME
 JSFLAGS += -s MODULARIZE=1
 JSFLAGS += -s EXPORT_NAME=createModule