Improve boot time

  • I have a LoPY4 and ran some deep sleep cycle tests. I can get the sleep current down to about 15uA. I have found that the boot time from a deep sleep reset is about 4.5 seconds though which is concerning.

    Is there some way to reduce the time it takes to wake from deep sleep? Alternatively, is there someway to reduce the current consumption during boot from 50mA to 1 or 2 mA?

    The boot time is quite a large amount of time. The duty cycle required to average down the wake current of about 50mA to about 200 uA is at least 250:1 or more. For 4.5 seconds that works out to about 19 minutes. For my application I would prefer that updates be sent closer to once every 2 minutes. To accomplish that, I need to get the time the LoPY4 is on down to about 0.5 sec. Is there any possibility that can be done?

  • @jcaron With version 1.14.0.b1 I get 1.6 seconds.

  • @jcaron
    I think it was L01 because the application from the first post in that thread was written for sensor based on L01.

    In all tests the application was frozen during firmware build time.

  • @jcaron The only import I had is machine for the Pin to signal the presence of boot. And obviously the stuff from

    # -- always run on boot-up, even during safe boot
    import os
    from machine import UART
    os.dupterm(UART(0, 115200))

    I removed that and got 1.77 seconds.
    Now, with these line, the LoPy4 shows 1.87 seconds. But after all, not a big variation.

  • @robert-hh Can you reproduce @danielm 's second test in that thread? I'm surprised he got about 500 or 800 ms depending on the firmware version and you get nearly 2 seconds. Unless you're importing some module that really takes a long time to load, but he already had imports of machine, pycom and os.

    @danielm What device where you using in those tests? I guess a LoPy or LoPy 4?

  • @jcaron Just for completion other boot times:

    • WIPy3 (clone): ~1.8 s.
    • FiPy: ~1.95 s

    So it#s all in the same range.

  • @danielm Thanks.

    There was indeed a 300 ms increase in boot time between the two, but the total boot time remained under a second.

    I wonder how long it actually takes to load and compile a relatively simple script such as OP's, and how long it takes for the various imports.

  • This is the thread where I described the issue with boot time being longer for FW 1.18.0 in comparison to FW 1.14.0.b1 while running the same code:

    I did not perform tests with development FW 1.19.0 yet and the source of the issue remains unclear.

  • @sympatron As far as I can tell, this is the minimum boot time, unless you start to tweak the firmware. And to my surprise, lopy1 and lopy4 are the same. I should say, that the firmware version is 1.18.1.r1.

  • @robert-hh said in Improve boot time:

    @jcaron I tested the boot time on a LoPy4 and a LoPy1 as the time between the rising edge of Reset and a Pin pulse cause by a few lines in This time is 1.97 seconds. From then on, control is by the user scripts.

    Does that mean that ~2s is the absolute minimum boot time or do you know of any why to speed it up it further?
    Is the boot time for LoPy1 and 4 the same?

  • @jcaron I tested the boot time on a LoPy4 and a LoPy1 as the time between the rising edge of Reset and a Pin pulse cause by a few lines in This time is 1.97 seconds. From then on, control is by the user scripts.

  • @sslupsky 3 seconds still seems to be a bit long, but I have no experience with the LoPy 4, only the original LoPy.

    Also, check the firmware release announcement threads, I believe someone mentioned one of the versions increasing boot time, not sure if that was fixed since then (and/or if that was in the stable or dev versions). Which firmware version are you running BTW?

  • @jcaron Somewhere here I recall someone said to disable bluetooth to minimize power. I updated my code to remove the Bluetooth and that shaved about 0.4 sec from the boot it seems.

    I added a timer that starts at the beginning of main and stops at the end just before the sleep. I timed the loop with the debug on which was 18.6 sec. The timer reported 6.6 sec in main. Using these figures it appears the boot time is 18.6 - 6.6 - 10 = 2.0 sec. There is about 0.4 sec delay so factoring that indicates boot time is about 1.6 sec.

    Thanks for the feedback.

  • @sslupsky

    Switch off your debug_print. Sending the text over the serial needs time. Addtional there is an unecessary sleep after the prrint.

  • @sslupsky See my answer in the other thread.

    Your 14-15 seconds include:

    • 10 seconds deep sleep
    • boot time
    • LoRaWAN send time (not much, you're at SF7, so less than 100 ms)
    • RX1 and RX2 (at least 2 seconds, possibly more if the network sends a higher RX delay)
    • possibly receive time

    Your boot time is thus at most 3 seconds, not 4.5...

    Why are you touching Bluetooth? IIRC there's no need to.

  • @sslupsky Loading modules is much faster if the are pre-compiled with mpy-cross. But you cannot do that with So you have to put the bulk of you code into a different script, and in you simply import that. Since your script is not very long, the overall boot time improvement is not that good.

  • @rcolistete @jcaron Thank you for the feedback. I overlooked that micropython needs to load the modules each time. That likely explains the long boot time.

    The cycle time of the code segment below measured from Wake to Wake is about 14.5 - 15 seconds when I disable the debug (print's, blinks and pause). The sleep time is 10 seconds.

    Here is the code I am using for the test.

    from network import Bluetooth
    import pycom
    if pycom.heartbeat() == True:
    if pycom.wifi_on_boot() == True:
    bluetooth = Bluetooth()

    from network import LoRa
    from network import Bluetooth
    import socket
    import pycom
    import time
    import ubinascii
    import config
    import struct
    from machine import ADC
    import machine
    def hello():
      debug_print("debug", "Hello")
      blink(2, 0x00FF00)
    def select_subband(lora, subband):
      if (type(subband) is int):
        if ((subband<1) or (subband>8)):
          raise ValueError("[LoRa] subband out of range (1-8)")
        raise TypeError("[LoRa] subband must be 1-8")
      for channel in range(0, 72):
      for channel in range((subband-1)*8, ((subband-1)*8)+8):
        lora.add_channel(channel, frequency=902300000+channel*200000, dr_min=0, dr_max=3)
      lora.add_channel(63+subband, frequency=903000000+((subband-1)*1600000), dr_min=4, dr_max=4)
    def blink( num=1, color=0x0000FF ):
      if DEBUG_LED:
        for n in range(0, num):
    def debug_print( type, msg ):
      if DEBUG_PRINT:
        print( "[", type, "] ", msg)
    LORA_SUBBAND = const(1)
    LORA_NODE_DR = const(3)
    SLEEP_TIME = const(10)
    DEBUG_PRINT = True
    DEBUG_LED = True
    DEBUG_PAUSE = False
    # Initialize ADC
    esp32adc = ADC(0)
    # Initialise LoRa in LORAWAN mode.
    lora = LoRa(mode=LoRa.LORAWAN, region=LoRa.US915)
    resetCause = machine.reset_cause()
    wakeReason = machine.wake_reason()
    # reset and wake reasons
    debug_print("machine", "Reset cause: " + str(resetCause))
    debug_print("machine", "Deep sleep wakeup reason: " + str(wakeReason))
    debug_print("machine", "Approximate deep sleep time remaining: " + str(machine.remaining_sleep_time()) + " millisec")
    if resetCause == machine.PWRON_RESET:
    elif resetCause == machine.WDT_RESET:
    elif resetCause == machine.DEEPSLEEP_RESET:
    if wakeReason[0] == machine.PWRON_WAKE:
      # should the LoRa context be reset here?  ie:  lora.nvram_erase() ?
    elif wakeReason[0] == machine.RTC_WAKE:
      # restore LoRa context if wake from sleep
      debug_print("LoRa", "Restoring LoRa context ...")
    # configure ADC
    esp32adc_c ='P13')
    # configure LoRa
    select_subband(lora, LORA_SUBBAND)
    dev_eui = lora.mac()
    debug_print("LoRa", "dev_eui = " + ubinascii.hexlify(dev_eui).upper().decode('utf-8'))
    # create an OTAA authentication parameters
    app_eui = ubinascii.unhexlify('redacted')
    app_key = ubinascii.unhexlify('redacted')
    joinAttempts = 0
    if not lora.has_joined():
      # wait until the module has joined the network
      while not lora.has_joined() and joinAttempts < 10:
        # join a network using OTAA (Over the Air Activation)
        lora.join(activation=LoRa.OTAA, auth=(dev_eui, app_eui, app_key), timeout=0)
        if lora.has_joined():
          debug_print("LoRa", "Successfully joined LoRa network")
          blink(2, 0x0000FF)
          debug_print("LoRa", "LoRa network not yet joined...")
          joinAttempts += 1
      if not lora.has_joined() and joinAttempts >= 10:
        debug_print("LoRa", "Failed to join LoRa network")
      debug_print("LoRa", "In LoRa network")
      blink(1, 0x0000FF)
    if lora.has_joined():
      # create a LoRa socket
      s = socket.socket(socket.AF_LORA, socket.SOCK_RAW)
      # set the LoRaWAN data rate
      s.setsockopt(socket.SOL_LORA, socket.SO_DR, LORA_NODE_DR)
      # make the socket blocking
      # (waits for the data to be sent and for the 2 receive windows to expire)
      # send some data
      value = esp32adc_c.value()
      debug_print("adc", "value: " + str(value))
      payload = value.to_bytes(2, "little")
      # make the socket non-blocking
      # (because if there's no data received it will block forever...)
      # get any data received (if any...)
      data = s.recv(64)
      debug_print("debug", data)
    # wait after wake
    blink(1, 0xFF0000)
    debug_print("debug", "Press CTRL-F to soft reset and drop back to RLE")
    debug_print("debug", "Done")
    # Prepare LoRa to sleep
    if lora.has_joined():
    debug_print("debug", "Going to sleep for " + str(SLEEP_TIME) + " seconds ...")
    blink(3, 0x00FF00)
    # deep sleep
    machine.deepsleep(SLEEP_TIME * 1000)

  • @sslupsky Which MicroPython modules are you loading after each boot/wake up from deep sleep ?

    As LoPy4 uses PSRAM (with SPI interface) it is slower than LoPy (v1) to acess RAM memory and to load MicroPython modules to the RAM memory. E. g., LoPy4 takes 1.0s to load some modules, LoPy v1 takes only 0.4s.

  • @sslupsky 4.5 seconds seems a bit long. Don't have a LoPy 4, and haven't tried with recent firmware versions, but in my experience (with a LoPy, and Pysense-controlled deep sleep, so closer to a cold boot), boot time was about 1.5 to 2 seconds IIRC.

    Have you disabled WiFi on boot? What is your reference point for boot complete? Start of the boot script, or after you have done some other stuff?

    I believe there was some discussion a little while ago about the boot time increasing a lot in a recent firmware release, maybe that's related.

    Pretty sure you can do better than 4.5 seconds, but I'm not sure you'll get to 0.5 seconds.

Pycom on Twitter