Jetson Nano

This page details the procedure (valid in January 2023) for using a Jetson Nano with a LimeSDR Mini all controlled by a Portsdown (2020 or 4) for H265 DATV transmissions.

There are 2 supported configurations:

• As first described in CQ-TV 265 (2019) using an LKV373 for HDMI input and a network router to isolate the external LAN from the broadcast UDP used by the LKV373.
• A simpler configuration using USB-connected input devices, controlled by a Portsdown 4 or Portsdown 2020.

This page now describes the simpler configuration. The LKV373 configuration is described here Jetson Nano LKV373

Supported sources include:

• ATEM Mini Pro and ATEM Mini
• EagleEye Mini USB Camera with (standard Portsdown) USB Mic dongle
• Elgato Camlink 4K HDMI Dongle
• Raspberry Pi Camera Version 2 connected to the Jetson through a CSI ribbon with (standard Portsdown) USB Mic dongle

Software Build for the Jetson Nano (updated 3 Feb 23)

To start with, you need a Jetson Nano 4GB, a 32 GB SD Card (Sandisk Ultra 10 recommended), a 4A 5V PSU with a 2.1mm power plug, a 0.1 inch jumper, an HDMI monitor, a USB Mouse and a USB keyboard. The 2 GB Jetson Nano might work (and will need a different SD Card Image) but has not been tested.

Fit the jumper link to the Nano PCB at J48 to select the use of the 2.1mm power socket, and connect the HDMI monitor, keyboard and mouse. and also a wired network connection with internet access. The monitor, keyboard and mouse are only required during the set-up phase.

On another computer, download the Jetson Nano Disk image from the links just under "JETSON NANO DEVELOPER KITS" on this page Jetpack SDK 4.6.3. The direct link for the download is here. You should download a 6.4 GB file called jetson-nano-jp461-sd-card-image.zip. Later versions of the "Jetpack" may or may not work.

Unzip the file (resulting in a 13.4 GB file called sd-blob-b01.img) and use Win32 Disk Imager or Etcher to write it to your SD Card. No additional files are required on the card - simply insert it into the Jetson and boot up.

On boot, first accept the licence agreement, then select your language, then you keyboard layout and timezone. Then fill in the following fields:

Your name:             Your first name
Your computer's name:  jetson-nano
Pick a username:       nano
Choose a password:     jetson
Confirm your password: jetson

and select "Log in automatically"

Then accept the default APP Partition Size (30422) and the default Nvpmodel Mode. The system will reconfigure and reboot.

After the reboot, close the keyboard shortcuts, then go through the gnome-initial-setup, selecting "No, dont send system info".

Click on "System Settings" (the cogwheel and spanner) in the left hand sidebar, then select "Security and Privacy" and in the Security tab untick "Waking from Suspend" and Returning from blank screen". Close the window with the orange cross in the top left corner.

Next, open a terminal window (right click on the desktop and click terminal)) to check the Jetson IP address:

ifconfig eth0

You will see the IP address in the second line of the response after the word inet. Make a note of it for later. Then download the install script, make it executable and run it:

wget https://github.com/davecrump/portsdown4/raw/master/install_for_nano.sh
chmod +x install_for_nano.sh
./install_for_nano.sh

If prompted to install a new version of any file, select Y. Also, select Yes to automatically restart the Docker daemon. If asked whether you want to minimise the installation, say no.

Eventually, the Jetson will reboot. You can then disconnect the HDMI monitor, keyboard and mouse. Connect the LimeSDR Mini to the Jetson (and the ATEM or webcam).

Setting Up the Portsdown

Set the Jetson Ip address in the Portsdown by selecting Menu3, Jetson/LKV Config, Set Jetson IP Address. Correct connection can be observed by the "Shutdown Jetson" and "Reboot Jetson" buttons being Blue, not Grey.

Next, the SSH connection to the Jetson needs to be checked. Log in to your Portsdown by SSH and go to the command line. Then enter

ssh nano@<Jetson IP address>

for example

ssh nano@192.168.2.139

If you see a "WARNING REMOTE HOST IDENTIFICATION HAS CHANGED", enter

ssh-keygen -f "/home/pi/.ssh/known_hosts" -R "<Jetson IP address>"

for example

ssh-keygen -f "/home/pi/.ssh/known_hosts" -R "192.168.2.139"

now try again

ssh nano@<Jetson IP address>

you should get a prompt "Are you sure you want to continue connecting (yes/no)?". Type yes and press enter. Now enter the password (jetson). After the cionnection is established, type exit and press enter to close it.

If, on initially typing

ssh nano@<Jetson IP address>

you get a prompt for the password, all is well and you can press ctrl-c to cancel it and continue.

These 2 steps need to be repeated for each Portsdown that you use to control the Jetson.

Control from the Portsdown Touchscreen

Use the touchscreen to select:

• Output to: Jetson Lime
• Encoder: H265
• Source:

1. HDMI for ATEM Mini Pro or Elgato Camlink 4K (only one should be connected at a time)
2. Webcam for EagleEye Mini webcam connected to the Jetson
3. Pi Cam for a Raspberry Pi Camera V2 connected to the Jetson

• Audio: Auto for HDMI Audio, USB Mic for USB Audio Dongle

Then you can select other settings (Modulation, Frequency, Symbol Rate, FEC and Lime Gain) as required. Testing has only been conducted over a narrow range of SRs and FECs. 333 kS, FEC 2/3 is a good starting point. You may find that some selections you want to make are greyed-out; select them anyway - the combinations above are valid.

When you shut down your Portsdown using the touchscreen ShutDown button, it will send a ShutDown signal to the Jetson as well, allowing a graceful shutdown of the Jetson without the use of a screen and keyboard.

The GPIO pin 40 on the Jetson can be used to key PAs as it is programmed to go high 15 seconds after TX selection and go low at the end of the transmission. However, please see the warning about GPIO behaviour below.

Working Configurations

Due to limited time only a few specific configurations have been developed and tested so far:

• H265 Test Card with no audio (select Source TestCard)
• H265 Elgato Camlink 4K HDMI Capture USB video and audio (select Source HDMI and Audio "Auto")
• H265 Elgato Camlink 4K HDMI Capture USB Video with audio from USB Mic dongle (select Source HDMI and Audio "USB Mic")
• H265 ATEM Mini Pro USB video and audio (select Source HDMI and Audio "Auto")
• H265 ATEM Mini Pro USB Video with audio from USB Mic dongle (select Source HDMI and Audio "USB Mic")
• H265 Polycom EagleEye Mini USB Webcam with Audio from USB Mic dongle (select Source Webcam)
• H265 Raspberry Pi Camera V2 connected to Jetson by CSI with Audio from USB Mic dongle (select Source Pi Cam)

Note that if both the Elgato CamLink 4K capture device and the ATEM Mini Pro are connected by USB, the Elgato is used as first preference when HDMI is selected as a source. Both these devices need a USB 3.1 cable for connection.

Both the LimeSDR Mini V1 and LimeSDR Mini V2 are supported.

Performance

Sadly, the Jetson is 2019 technology, and its performance has been eclipsed by modern PC cards. The practical resolution limit for H265 333 kS FEC 2/3 is 720x1280 (720p). For 1080p, 1 MS FEC 2/3 is required. The Jetson/Lime combination struggles to transmit at more than 2 MS.

PTT Switching

The Jetson GPIO pin 40 is set high when it is safe to energise the PA (after the LimeSDR calibration spike). This occurs about 15 seconds after the transmit selection. The controlling Portsdown GPIO pin 40 is also set high at about the same time. There is no PTT signal (or band switching signal) on the LimeSDR Mini GPIO connector.

Note that the Jetson GPIO interface is not as robust as the Raspberry Pi GPIO and tends to latch-up if abused. It is recommended that an opto-isolator is used for isolation.

Problem Solving

This is a complex configuration to get working. Some pointers if it does not work for you:

• Make sure that the Jetson 5v power supply and cabling is good quality. The Jetson can accept 5.25 V, so aim to give it 5.2 V at the barrel connector. The LimeSDR Mini likes to have at least 5.0v to the LimeSDR Mini during transmit. Measure this voltage on the edge connections of the LimeSDR Mini. Lower voltages may not be reliable.
• If the Jetson IP address changes, you will need to change it in the Portsdown settings AND re-approve the SSH connection from the Portsdown to the Jetson - just like you did in the set-up procedure. Setting your router to always give the Jetson the same IP address can help prevent this.
• The Pi Cam and EagleEye camera sources will not work unless a compatible USB Audio dongle is connected to the Jetson.
• The ATEM and the Camlink 4K need to be connected to the Jetson with USB 3.1 cables (the blue connectors with the extra pins), not USB 2 cables.
• Sometimes if the transmit selection is cancelled before the Jetson starts transmitting, the ATEM gets de-registered on the USB and is invisible to the Jetson. This shows as a DVB-S2 lock with no service information or video. The cure for this is to come out of transmit, recycle the power to the ATEM, pause for a few seconds and then reseklect transmit.

Hardware

Power Draw

Measured at a supply of 5.1V into the DC barrel jack connector. >5V measured on the GPIO header.

• CPU Frequencies at default: 0.3 - 0.6A depending on CPU & Network load
• CPU Frequencies at max: 0.45 - 0.9A depending on CPU & Network load
• CPU at max, LimeSDR Mini & C920 at 1MS 1080p H.265 DVB-S2 transmit: 1.8 - 1.9A

GPIO

The GPIO pinout of the Jetson Nano can be found here: https://www.jetsonhacks.com/nvidia-jetson-nano-j41-header-pinout/

Note that when not initialised in sysfs (ie. straight after power-on), the GPIO pins appear to be able to be latched up from their default 0V state to a 3.3V high, or an unstable ~1.4V state by simply touching a scope or multimeter probe to the pin. The exact characteristic of this behaviour isn't yet understood but it is worrying for PA PTT control and similar applications.

Fan

PWM fans are available however the use of a non-PWM 5V fan will cause the fan to simply run all the time (including when the Jetson is shutdown), removing the requirement for the fan to be manually started in software after boot. When using PWM, set a value where the fan runs slowly but reliably to minimise noise. There is some code here https://github.com/Pyrestone/jetson-fan-ctl or here https://github.com/hooperbill/fan-daemon for automatic fan speed control. Manually:

sudo sh -c 'echo XXX > /sys/devices/pwm-fan/target_pwm' where XXX is a number between 0 and 255 setting the PWM speed.

The holes in the heatsink can be tapped for M3 bolts, or can be drilled out. Note that the fins below the holes prevent more than ~3mm of the bolt from protruding below.