feat(esptool): Add --retry-open-serial flag, config file entry and envar

`esptool` frequently fails when trying to open the serial port of a device
which deep-sleeps often:

$ esptool.py --chip esp32s3 -p /dev/cu.usbmodem6101 [...] write_flash foo.bin
Serial port /dev/cu.usbmodem6101

A fatal error occurred: Could not open /dev/cu.usbmodem6101, the port is busy or doesn't exist.
([Errno 35] Could not exclusively lock port [...]: [Errno 35] Resource temporarily unavailable)

This makes developers add unnecessarily long sleeps when the main CPU is awake, in order to give
`esptool` the chance to find the serial port.

This PR adds a new flag `--retry-open-serial` (with corresponding env variable and cfg file entry)
which retries opening the port indefinitely until the device shows up:

$ esptool.py --chip esp32s3 -p /dev/cu.usbmodem6101 [...] write_flash --retry-open-serial foo.bin
Serial port /dev/cu.usbmodem6101
[Errno 35] Could not exclusively lock port [...]: [Errno 35] Resource temporarily unavailable
Retrying to open port .........................
Connecting....
Chip is ESP32-S3 (QFN56) (revision v0.2)
[...]

docs/en/esptool/configuration-file.rst

@@ -109,6 +109,8 @@ Complete list configurable options:
 +------------------------------+-----------------------------------------------------------+----------+
 | custom_reset_sequence | Custom reset sequence for resetting into the bootloader | |
 +------------------------------+-----------------------------------------------------------+----------+
+| retry_open_serial | Retry opening the serial port indefinitely | False |
++------------------------------+-----------------------------------------------------------+----------+
 
 Custom Reset Sequence
 ---------------------

esptool/__init__.py

@@ -35,6 +35,7 @@
 import os
 import shlex
 import sys
+import termios
 import time
 import traceback
 
@@ -66,7 +67,7 @@
  write_mem,
 )
 from esptool.config import load_config_file
-from esptool.loader import DEFAULT_CONNECT_ATTEMPTS, StubFlasher, ESPLoader, list_ports
+from esptool.loader import DEFAULT_CONNECT_ATTEMPTS, StubFlasher, ESPLoader, list_ports, cfg
 from esptool.targets import CHIP_DEFS, CHIP_LIST, ESP32ROM
 from esptool.util import (
  FatalError,
@@ -77,6 +78,9 @@
 
 import serial
 
+# Retry opening the serial port indefinitely
+DEFAULT_RETRY_OPEN_SERIAL = cfg.getboolean("retry_open_serial", False)
+
 
 def main(argv=None, esp=None):
  """
@@ -186,6 +190,16 @@ def main(argv=None, esp=None):
  default=os.environ.get("ESPTOOL_CONNECT_ATTEMPTS", DEFAULT_CONNECT_ATTEMPTS),
  )
 
+ parser.add_argument(
+ "--retry-open-serial",
+ help=(
+ "Retry opening the serial port indefinitely. "
+ "Default: %s" % DEFAULT_RETRY_OPEN_SERIAL
+ ),
+ default=os.environ.get("ESPTOOL_RETRY_OPEN_SERIAL", DEFAULT_RETRY_OPEN_SERIAL),
+ action="store_true",
+ )
+
  subparsers = parser.add_subparsers(
  dest="operation", help="Run esptool.py {command} -h for additional help"
  )
@@ -768,6 +782,7 @@ def add_spi_flash_subparsers(
  port=args.port,
  connect_attempts=args.connect_attempts,
  initial_baud=initial_baud,
+ retry_open_serial=args.retry_open_serial,
  chip=args.chip,
  trace=args.trace,
  before=args.before,
@@ -1092,11 +1107,50 @@ def expand_file_arguments(argv):
  return argv
 
 
+def get_default_specific_connected_device(
+ chip, each_port, initial_baud, trace, before, connect_attempts, retry_open_serial
+):
+ retry_attempts = 0
+ _esp = None
+ while True:
+ try:
+ chip_class = CHIP_DEFS[chip]
+ _esp = chip_class(each_port, initial_baud, trace)
+ _esp.connect(before, connect_attempts)
+ if retry_attempts > 0:
+ # break the retrying line
+ print("")
+ return _esp
+ except (
+ FatalError,
+ serial.serialutil.SerialException,
+ IOError,
+ OSError,
+ termios.error,
+ ) as e:
+ if not retry_open_serial:
+ raise
+ if _esp and _esp._port:
+ _esp._port.close()
+ _esp = None
+ if retry_attempts == 0:
+ print(e)
+ print("Retrying failed connection ", end="", flush=True)
+ else:
+ if retry_attempts % 9 == 0:
+ # print a dot every second
+ print(".", end="", flush=True)
+ time.sleep(0.1)
+ retry_attempts += 1
+ continue
+
+
 def get_default_connected_device(
  serial_list,
  port,
  connect_attempts,
  initial_baud,
+ retry_open_serial=False,
  chip="auto",
  trace=False,
  before="default_reset",
@@ -1110,9 +1164,15 @@ def get_default_connected_device(
  each_port, initial_baud, before, trace, connect_attempts
  )
  else:
- chip_class = CHIP_DEFS[chip]
- _esp = chip_class(each_port, initial_baud, trace)
- _esp.connect(before, connect_attempts)
+ _esp = get_default_specific_connected_device(
+ chip,
+ each_port,
+ initial_baud,
+ trace,
+ before,
+ connect_attempts,
+ retry_open_serial,
+ )
  break
  except (FatalError, OSError) as err:
  if port is not None:
@@ -1229,6 +1289,7 @@ def _main():
  try:
  main()
  except FatalError as e:
+ print(traceback.format_exc())
  print(f"\nA fatal error occurred: {e}")
  sys.exit(2)
  except serial.serialutil.SerialException as e:

esptool/config.py

@@ -20,6 +20,7 @@
  "write_block_attempts",
  "reset_delay",
  "custom_reset_sequence",
+ "retry_open_serial",
 ]