Scanning for heartbeat messages & using AT commands(?)

I have several questions about the 3DR radios that I was hoping some developers might be able to answer to facilitate my thesis research...

[1] The 3DR wiki says 8 parameters must be the same for two 3DR radios to communicate, but I cannot find a fixed possible parameter value for two of these parameters (firmware version & LBT_RSSI)... can there be an infinite possible values for these parameters?

[2] I've tried using AT commands in the Linux terminal to change the values of these parameters, but I am getting no response at all from the 3DR ground-module... what are the proper Linux terminal commands (or other process, e.g. bash scripting) to modify individual parameters of the 3DR (USB) ground module?? Here's what I tried that elicited no response from the 3DR ground-module:

user@linux:~/MAVProxy# stty < /dev/ttyUSB0

speed 57600 baud; line = 0;

min = 0; time = 0;

-brkint -icrnl -imaxbel

-opost

-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

user@linux:~/MAVProxy# echo "+++" > /dev/ttyUSB0

user@linux:~/MAVProxy# echo "ATi" > /dev/ttyUSB0

user@linux:~/MAVProxy# echo "ATI" > /dev/ttyUSB0

user@linux:~/MAVProxy# echo "ATi5" > /dev/ttyUSB0

user@linux:~/MAVProxy# echo "ATI5" > /dev/ttyUSB0

user@linux:~/MAVProxy# echo "ATi+++" > /dev/ttyUSB0

always: nothing

[3] Could a 3DR ground-module be used to manually broadcast a heartbeat message? (e.g. using the the 3DR radio as an interface for Scapy to broadcast the MAVLink heartbeat message with rapidly changing & widely varying GPS data)

I would immensely appreciate answers to any/all of these, is it will greatly aid in conducting my experiments... THANKS!

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Hi Joe,

I'd recommend you install and use mavproxy on Linux. Do this:

  apt-get install python-pip

  pip install pymavlink mavproxy

The to connect to the radios use:

  mavproxy --baudrate 57600 --master /dev/serial/by-id/FTDI* --setup

then use +++ followed by enter to get the OK prompt

Then try:

ATI

and follow the rest of the commands from the docs

Re your other questions. Firmware version is a 32 bit number, so 4 billion possible values. LBT_RSSI can only be in the range 0 to 255.

The 3DR radios are point to point, and don't currently have the concept of a broadcast.

Cheers, Tridge

THANKS Tridge!!! Your answers help a lot with my calculations.

Just FYI — on my system the USB ground module doesn't begin with "FTDI" in the "/dev/serial/by-id/" directory, it begins with "usb"... fortunately I know my way around linux so I easily corrected the syntax using "/dev/ttyusb0" to make it work; I just mention it in case some one else comes along and tried the exact instruction you provided and wonders why it didn't work.

[3] Perhaps "broadcast" was the wrong word to use then... (question rephrased) Could a 3DR USB "ground" module be used to manually transmit a heartbeat message? or is only the "air" module configured to do that? If it is possible, how would one go about transmitting a heartbeat MAVLink message from the "ground" module??

Thanks again for your time & assistance!!

— joe

Any idea why MAVproxy won't load the map module? I receive the following error message:

Unable to load module map: No module named cv2.cv

Thanks!

—joe

you need to install the python-opencv package.

Thanks again, Tridge! I've been using MAVProxy a lot (you're right — it's awesome)... but I've run into a confusing problem I hoped you could help me resolve...

The end goal is to monitor the latency of the network. I thought I could accomplish this by modifying your MAVProxy script — I added the following function after your "cmd_link(args)" function:

def cmd_monitor(args):
    '''Monitor Data-Link'''
    sec = 0
    try:
        while sec < 900:
            print(time.strftime("%Y-%m-%d %H:%M:%S", time.gmtime()))
            cmd_link(1)
            time.sleep(1)
            sec = sec + 1
    except KeyboardInterrupt as k:
        print ("[+]Ending Data-link Monitor")
    except Exception as e:
        print("[!]An exception has occurred",e)
    except:
        print ("[-]Unknown exit reason")
    return

And I added the command option "monitor" from the menu displayed when the user types "help" in MAVProxy. It "works" to an extent... here's the differences between monitoring the data-link manually and monitoring it through the automated script (function above):

MANUAL monitoring

Notice how the number of packets steadily increases AND the packet loss (number & %) occasionally changes...

AUTOMATED monitoring

Notice how, when using my "cmd_monitor()" function (via the "monitor" command) EACH VALUE remains constant... [wtf?]

Just to show it's not always the same values, here's another run using the function:

See? Different times, different # of packets, different # of packets lost & % loss, but all constant.

How can I fix my function to get it to report the latency (via "link" command) every second for 15 minutes? Or, do you know of a better way to accomplish my goal of monitoring the network latency?

[FYI— I'm doing this so I can quantitatively compare the latency when MAVLink is not secure to when authenticated encryption is used]

Thanks for your help! So far it's been quite fruitful, but I'm having trouble in the APM code now for which I hoped you might have some guidance:

WHERE (and how) would you modify the APM code to perform an XOR on the message payload immediately following message receipt & preceding message transmission??

I thought only "mavlink_helpers.h" would have to be modified in the function 

MAVLINK_HELPER void _mav_finalize_message_chan_send(mavlink_channel_t chan, uint8_t msgid, const char *packet, uint8_t length) [line 132] 

for encryption, and in the function 

MAVLINK_HELPER uint8_t mavlink_parse_char(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status) [line 407] 

for decryption... am I wrong?

The aforementioned changes can be viewed in the modified version of the file I pasted here. Again, the goal is to have the message payload XORd "in flight" (so the APM & Mission Planner would XOR it back to readable form upon receipt for processing). I'm still awaiting feedback on the required cahnges to Mission Planner from Michael Oborne (here). THANKS!!!

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