Using the ymodem protocol to flash firmware

General
1

I know it’s possible to use the particle ‘–serial’ option, and the python script, which I’ve had limited success with, to upload firmware to a Core or Photon, but does anyone use a conventional serial terminal emulator to do that?

Reason for asking is that I usually compile using the Particle Docker image and then DFU flash using a second, bespoke, Docker image. That works well, but I’d to be able to flash the firmware serially from my Linux laptop rather than using my second Docker image.

2

I don’t understand - why does flashing from your laptop require use of a serial terminal rather than the python script?

3

Have a look at the script I created. Assuming you are using Ubuntu or another Debian based distro, it will install the particle toolchain, dfu-util and other dependencies.

I also recomend that you use my script’s patch option, which changes the baud rate for the Photon to trigger dfu mode to 19200, a baud rate that is more linux-friendly.

My script can be installed with

curl -fsSL https://git.io/vwRRf | bash

Read more over at my repository.

4

Sorry, my wording was unclear. I was wanting to know whether anyone uses a terminal emulator to flash firmware (ymodem), instead of using ‘–serial’ or the python script. I’ve tried using Linux/minicom but could not get it to work; I’m abandoning that idea now.

I do, however, have another workaround for the problem of how to trigger ymodem mode on some distributions of Linux. Linux doesn’t always regard 28800 baud as a standard speed, which is needed to trigger ymodem mode, and it fails to set it.

I know some people on this forum are changing the firmware to use a different trigger speed, but here is another way.

Problem: on my Linux laptop (Centos), the python script fails:

[tim@c7 ~]$ python ymodem2.py /dev/ttyACM0 firmware.bin
Traceback (most recent call last):
  File
"ymodem2.py", line 159, in <module>
    ymodem(sys.argv)
  File
"ymodem2.py", line 145, in ymodem
    ser =
serial.Serial(port, baudrate=28800)
  File
"/usr/lib/python2.7/site-packages/serial/serialutil.py", line 261, in
__init__
    self.open()
  File
"/usr/lib/python2.7/site-packages/serial/serialposix.py", line 282,
in open
self._reconfigurePort()
  File
"/usr/lib/python2.7/site-packages/serial/serialposix.py", line 417,
in _reconfigurePort
    set_special_baudrate(self,
custom_baud)
  File
"/usr/lib/python2.7/site-packages/serial/serialposix.py", line 60, in
set_special_baudrate
    raise
ValueError('Failed to set custom baud rate: %r' % baudrate)
ValueError: Failed to set custom baud rate: 28800

Workaround: I modified the python script to use current
speed, from:

ser = serial.Serial(port, baudrate=28800)

to

ser = serial.Serial(port)

To set the (non-standard) serial speed prior to invoking the python script it is necessary to call a Linux/C program that sets it using ‘ioctl’. I adapted some of the code at:

https://www.raspberrypi.org/forums/viewtopic.php?f=72&t=33315
and named it ‘set28800.c’. I won’t reproduce the code here because it’s fairly straightforward to work out from the examples in the link.

Set the serial speed immediately prior to invoking the python script, like this:

./set28800 && sleep 1 && python ymodem2.py /dev/ttyACM0 firmware.bin
5

Is there any advantage to using ymodem instead DFU-util? I’ve always used DFU to upload code to my Particle devices.

6

If you have DFU available, I’d always go with it, but the advantage of ymodem is that you don’t need dfu-util and/or drivers installed.

1 Like