Reliably kick Arduino Micro to bootloader - arduino

Question

I have a Arduino Micro connected via usb to my pc, showing up as /dev/arduino.
Now when I want to program it (it currently has the default bootloader from Arduino) I have to boot it into the bootloader. AFAIK this can be done by either resetting the chip or talking to it using the baudrate 1200.
For this I have a script like
#!/usr/bin/env python
import serial
s = serial.Serial(
port="/dev/arduino",
baudrate=1200,
bytesize=serial.EIGHTBITS,
stopbits=serial.STOPBITS_ONE,
parity=serial.PARITY_NONE)
s.isOpen()
s.close()
The problem is, that the script as well as the reset pin do not work reliably. Also cutting the power source from the device usually does not kick it into bootloader.
How can I reliably put my Arduino Micro into bootloader? Preferably over USB.

Answer 1

The Python script you posted really should work. You did not say what your evidence is for why it is not working so I can only guess what might be the problem. My guess would be that you need to add a delay after closing the port because it will take some time for the computer to detect the bootloader, enumerate it, and create the serial ports for it. A delay of one or two seconds ought to be enough.
Another guess would be that the code you are running on your Arduino Micro interferes with USB interface. For example, you might have an interrupt service routine that runs for a long time or you might be disabling interrupts in your mainline code for a long time. If you don't let the Arduino's USB interrupts run promptly, they cannot do their job reliably.

Answer 2

the magic isn't within the arduino IDE but instead on the avrdude sequence.
you can install another avrdude on your system, or use the same one which comes with arduino, but you can make a reset simulating a small signature read with avrdude (avrdude -c arduino -p m328p -P com1)...
but to be completely honest, the real trick is on the arduino's reset circuit. the reset pin is connected to serial DTR via a capacitor (and sometimes rts), so each time avrdude switch the serial configuration to program via rs232 it produce a small pulse on DTR (about 50ms it seems) which causes a reset on the microcontroller. i think you can use s.setDTR(True); time.sleep(0.05); s.setDTR(False) to generate a small pulse to reset your arduino within python...
good luck