flash_usb: Improve USB reconnect timing

Instead of waiting one second after entering bootloader mode, wait for
the device file to reappear.  This should make the flashing more
resilient to slight timing difference in the OS.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

scripts/flash_usb.py

@@ -17,12 +17,12 @@ def enter_bootloader(device):
         fcntl.ioctl(fd, termios.TIOCMBIS, struct.pack('I', termios.TIOCM_DTR))
         t = termios.tcgetattr(fd)
         t[4] = t[5] = termios.B1200
+        sys.stderr.write("Entering bootloader on %s\n" % (device,))
         termios.tcsetattr(fd, termios.TCSANOW, t)
         fcntl.ioctl(fd, termios.TIOCMBIC, struct.pack('I', termios.TIOCM_DTR))
         f.close()
     except (IOError, OSError) as e:
         pass
-    time.sleep(1.0)
 
 # Translate a serial device name to a stable serial name in /dev/serial/by-path/
 def translate_serial_to_tty(device):
@@ -45,14 +45,37 @@ def translate_serial_to_usb_path(device):
     m = ttypath_r.match(lname)
     if m is None:
         raise error("Unable to find tty usb device")
-    return m.group("path")
+    devpath = os.path.realpath("/sys/class/tty/%s/device" % (fname,))
+    return m.group("path"), devpath
+
+# Wait for a given path to appear
+def wait_path(path, alt_path=None):
+    time.sleep(.100)
+    start_alt_path = None
+    end_time = time.time() + 4.0
+    while 1:
+        time.sleep(0.100)
+        cur_time = time.time()
+        if os.path.exists(path):
+            sys.stderr.write("Device reconnect on %s\n" % (path,))
+            time.sleep(0.100)
+            return path
+        if alt_path is not None and os.path.exists(alt_path):
+            if start_alt_path is None:
+                start_alt_path = cur_time
+                continue
+            if cur_time >= start_alt_path + 0.300:
+                sys.stderr.write("Device reconnect on alt path %s\n" % (
+                    alt_path,))
+                return alt_path
+        if cur_time > end_time:
+            return path
 
 # Flash via a call to bossac
 def flash_bossac(device, binfile, extra_flags=[]):
     ttyname, pathname = translate_serial_to_tty(device)
     enter_bootloader(pathname)
-    if os.path.exists(ttyname) and not os.path.exists(pathname):
-        pathname = ttyname
+    pathname = wait_path(pathname, ttyname)
     baseargs = ["lib/bossac/bin/bossac", "-U", "-p", pathname]
     args = baseargs + extra_flags + ["-w", binfile, "-v"]
     sys.stderr.write(" ".join(args) + '\n\n')
@@ -64,7 +87,7 @@ def flash_bossac(device, binfile, extra_flags=[]):
         try:
             subprocess.check_output(args, stderr=subprocess.STDOUT)
             if "-b" not in extra_flags:
-                time.sleep(1.)
+                wait_path(pathname)
                 subprocess.check_output(args, stderr=subprocess.STDOUT)
         except subprocess.CalledProcessError as e:
             pass
@@ -85,8 +108,9 @@ def flash_dfuutil(device, binfile, extra_flags=[], sudo=True):
     if hexfmt_r.match(device.strip()):
         call_dfuutil(["-d", ","+device.strip()] + extra_flags, binfile, sudo)
         return
-    buspath = translate_serial_to_usb_path(device)
+    buspath, devpath = translate_serial_to_usb_path(device)
     enter_bootloader(device)
+    pathname = wait_path(devpath)
     call_dfuutil(["-p", buspath] + extra_flags, binfile, sudo)