Add USB load test from Mark Whitehorn

Tools/usb_serialload.py

+import serial, time
+
+
+port = serial.Serial('/dev/ttyACM0', baudrate=57600, timeout=2)
+
+data = '01234567890123456789012345678901234567890123456789'
+#data = 'hellohello'
+outLine = 'echo %s\n' % data
+
+port.write('\n\n\n')
+port.write('free\n')
+line = port.readline(80)
+while line != '':
+    print(line)
+    line = port.readline(80)
+    
+
+i = 0
+bytesOut = 0
+bytesIn = 0
+
+startTime = time.time()
+lastPrint = startTime
+while True:
+    bytesOut += port.write(outLine)
+    line = port.readline(80)
+    bytesIn += len(line)
+    # check command line echo
+    if (data not in line):
+        print('command error %d: %s' % (i,line))
+        #break
+    # read echo output
+    line = port.readline(80)
+    if (data not in line):
+        print('echo output error %d: %s' % (i,line))
+        #break
+    bytesIn += len(line)
+    #print('%d: %s' % (i,line))
+    #print('%d: bytesOut: %d, bytesIn: %d' % (i, bytesOut, bytesIn))
+    
+    elapsedT = time.time() - lastPrint
+    if (time.time() - lastPrint >= 5):
+        outRate = bytesOut / elapsedT
+        inRate = bytesIn / elapsedT
+        usbRate = (bytesOut + bytesIn) / elapsedT
+        lastPrint = time.time()
+        print('elapsed time: %f' % (time.time() - startTime))
+        print('data rates (bytes/sec): out: %f, in: %f, total: %f' % (outRate, inRate, usbRate))
+        
+        bytesOut = 0
+        bytesIn = 0
+        
+    i += 1    
+    #if (i > 2): break
+