diff --git a/comm/SerialUSB/ring.SerialUSB.ino b/comm/SerialUSB/ring.SerialUSB.ino
new file mode 100644
index 0000000000000000000000000000000000000000..bbd5f9e9206925823d14c8aac196d836451dc6c2
--- /dev/null
+++ b/comm/SerialUSB/ring.SerialUSB.ino
@@ -0,0 +1,25 @@
+//
+// ring.SerialUSB.ino
+//
+// SerialUSB communication ring test
+//
+// Neil Gershenfeld 3/31/21
+//
+// This work may be reproduced, modified, distributed,
+// performed, and displayed for any purpose, but must
+// acknowledge this project. Copyright is retained and
+// must be preserved. The work is provided as is; no
+// warranty is provided, and users accept all liability.
+//
+
+void setup() {
+   SerialUSB.begin(0);
+   }
+
+void loop() {
+   while (true) {
+      if (SerialUSB.available()) {
+         SerialUSB.write(1+SerialUSB.read());
+         }
+      }
+   }
diff --git a/comm/pySerial/ring.pySerial.py b/comm/pySerial/ring.pySerial.py
new file mode 100755
index 0000000000000000000000000000000000000000..560aafd4dc9802eb89c1347864830298e57e66c0
--- /dev/null
+++ b/comm/pySerial/ring.pySerial.py
@@ -0,0 +1,38 @@
+#!/usr/bin/env python
+#
+# ring.pySerial.py
+#
+# pySerial communication ring test
+#
+# Neil Gershenfeld 3/31/21
+#
+# This work may be reproduced, modified, distributed,
+# performed, and displayed for any purpose, but must
+# acknowledge this project. Copyright is retained and
+# must be preserved. The work is provided as is; no
+# warranty is provided, and users accept all liability.
+#
+
+import serial,sys,time
+
+nloop = 10
+
+if (len(sys.argv) != 3):
+   print("command line: ring.pyserial.py serial_port port_speed")
+   sys.exit()
+port = sys.argv[1]
+speed = int(sys.argv[2])
+
+ser = serial.Serial(port,speed)
+ser.flushInput()
+x = 0
+start = time.time()
+for i in range(nloop):
+   while True:
+      ser.write(x.to_bytes(1,byteorder='big'))
+      x = int.from_bytes(ser.read(1),byteorder='big')
+      if (x == 0):
+         break
+end = time.time()
+print(f"byte ring cycles per second: {nloop*256/(end-start):6.3g}")
+