zephyr-flash-pyocd.bbclass: Flash the first probe found with a timeout

Currently the code flashes the firmware in a blocking way. If the host
is not configured accordingly (for example in terms of permissions),
this would hang undefinitely. This can easily confuse users and in order
to avoid this, the patch changes to unblocking session creation and
opening call, wrapping the tries in some relevant logging. The timeout
can be defined with `CONNECT_TIMEOUT_SECONDS` which defaults to 30
seconds.

Also, by default, when multiple probes are attached, the session call
will return a selection choice. This would obviously break under bitbake
with an exception:
    Exception: EOFError: EOF when reading a line
Avoid this by selecting the first found probe.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>
Signed-off-by: Naveen Saini <naveen.kumar.saini@intel.com>

classes/zephyr-flash-pyocd.bbclass

@@ -1,11 +1,27 @@
+CONNECT_TIMEOUT_SECONDS ?= "30"
+
 python do_flash_usb() {
     from pyocd.core.helpers import ConnectHelper
     from pyocd.flash.file_programmer import FileProgrammer
 
+    timeout = int(d.getVar('CONNECT_TIMEOUT_SECONDS'))
     image = f"{d.getVar('DEPLOY_DIR_IMAGE')}/{d.getVar('PN')}.elf"
     bb.plain(f"Attempting to flash {image} to board {d.getVar('BOARD')}")
 
-    with ConnectHelper.session_with_chosen_probe() as session:
+    # Try to connect to a probe with a timeout
+    now = 0
+    step = 3
+    while True:
+        session = ConnectHelper.session_with_chosen_probe(blocking=False, return_first=True)
+        if session:
+            break
+        if now >= timeout:
+            bb.fatal("Timeout while trying to connect to a probe. Make sure the target device is connected and the udev is configured accordingly. See <https://github.com/mbedmicro/pyOCD/tree/master/udev> for help.")
+        bb.warn("Can't connect to the probe. Retrying in %d seconds..." % step)
+        time.sleep(step)
+        now += step
+
+    with session:
         FileProgrammer(session).program(image)
         session.board.target.reset()
 }