How can I force an Arduino Leonardo to reset with AVRDUDE?

For uploading from Windows, I made a bat file wrapper for AVRDUDE.

It identifies the Leonardo COM port with WMI, resets this COM port to 1200 baud with the MODE command, identifies the bootloader COM port and invokes AVRDUDE.

The firmware is supposed to be placed in firmware.hex, but it can be changed to be supplied from the command line.

Code is in a GitHub repository, Arduino Leonardo Uploader

Or below:

@echo off
setlocal

for /f "tokens=1* delims==" %%I in ('wmic path win32_pnpentity get caption  /format:list ^| find "SparkFun Pro Micro"') do (
    call :resetCOM "%%~J"
)

:continue

:: wmic /format:list strips trailing spaces (at least for path win32_pnpentity)
for /f "tokens=1* delims==" %%I in ('wmic path win32_pnpentity get caption  /format:list ^| find "Arduino Leonardo bootloader"') do (
    call :setCOM "%%~J"
)

:: end main batch
goto :EOF

:resetCOM <WMIC_output_line>
:: sets _COM#=line
setlocal
set "str=%~1"
set "num=%str:*(COM=%"
set "num=%num:)=%"
set port=COM%num%
echo %port%
mode %port%: BAUD=1200 parity=N data=8 stop=1
goto :continue

:setCOM <WMIC_output_line>
:: sets _COM#=line
setlocal
set "str=%~1"
set "num=%str:*(COM=%"
set "num=%num:)=%"
set port=COM%num%
echo %port%
goto :flash

:flash
avrdude -v -C./avrdude.conf -patmega32u4 -cavr109 -P%port% -b57600 -D -V -Uflash:w:./firmware.hex:i

I had the same problem. I've tried opening and closing the ACM0 port with a Python script at 1200 baud, as someone already mentioned. It didn't work for me. Then I have received half-advice to try toggling RTS/DTS and that will make autoreset. So in the end I found the solution (at least for me) on Linux Mint 18.2 (Sonya):

#! /usr/bin/python

import sys
import serial

com = serial.Serial(sys.argv[1], 1200)
com.dtr=False
com.close()


python ./reset.py "/dev/ttyACM0"

dmesg shows me:

[21850.047120] cdc_acm 1-1:1.0: ttyACM0: USB ACM device
[22093.700327] usb 1-1: USB disconnect, device number 53
[22094.034133] usb 1-1: new full-speed USB device number 54 using xhci_hcd
[22094.175377] usb 1-1: New USB device found, idVendor=2341, idProduct=0036
[22094.175381] usb 1-1: New USB device strings: Mfr=2, Product=1, SerialNumber=0
[22094.175384] usb 1-1: Product: Arduino Leonardo
[22094.175387] usb 1-1: Manufacturer: Arduino LLC
[22094.175964] cdc_acm 1-1:1.0: ttyACM0: USB ACM device

I had the same issue on macOS, and I came up with the following Bash script:

# Find the Arduino port
ARDUINO_UPLOAD_PORT="$(find /dev/cu.usbmodem* | head -n 1)"

# Reset the Arduino
stty -f "${ARDUINO_UPLOAD_PORT}" 1200

# Wait for it...
while :; do
  sleep 0.5
  [ -c "${ARDUINO_UPLOAD_PORT}" ] && break
done

# ...upload!
avrdude "${OPTIONS[@]}"

The while loop is the trick! It's going to proceed as soon as the Arduino port is back online.

This is part of a Makefile I wrote for the project Sesame.