diff --git a/micros_test.py b/micros_test.py
new file mode 100644
index 0000000..642378c
--- /dev/null
+++ b/micros_test.py
@@ -0,0 +1,20 @@
+import pyb
+
+start = pyb.millis()
+count = 0
+while True:
+    pyb.disable_irq()
+    m = pyb.millis()
+    u = pyb.micros() & 0x7fffffff
+    pyb.enable_irq()
+    m2 = u // 1000
+    if m2 != m:
+        if m2 != (m + 1) or (u % 1000) > 100:
+            print("msec %d usec %d" % (m, u))
+            count += 1
+    if (m - start) >= 10000:
+        print('%4d err = %d' % (m // 1000, count))
+        start = m
+        if count > 0:
+            break
+