arm: add async tests

arm/test.py

@@ -0,0 +1,18 @@
+import serial
+
+s = serial.Serial('tty', 115200, timeout=6)
+length = 1
+
+log = open('test.log', 'wb')
+
+while True:
+    print(f'Writing {length} bytes')
+    s.write(b'b' * length);
+    data = s.read(length)
+    log.write(data)
+    if not data:
+        break
+
+    length += 1
+
+print(f'Read back 0 bytes')