Check bootloader logs via UART

Robotics & Edge Computing Jetson & Embedded Systems Jetson Xavier NX
1

Hi,

I have a Jetson Xavier NX board, with which I have connected a USB-TTL Serial cable. The cable is this which has

  • Red: +5V
  • Black: GND
  • Green: TxD
  • White: RxD

and the chip that is used is PL2303.

Here is the relevant output of dmesg | grep Prolific on my host machine:

[686342.604682] usb 1-1: new full-speed USB device number 62 using xhci_hcd
[686342.757633] usb 1-1: New USB device found, idVendor=067b, idProduct=2303, bcdDevice= 3.00
[686342.757646] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[686342.757652] usb 1-1: Product: USB-Serial Controller
[686342.757656] usb 1-1: Manufacturer: Prolific Technology Inc.
[686342.759409] pl2303 1-1:1.0: pl2303 converter detected
[686342.760425] usb 1-1: pl2303 converter now attached to ttyUSB0
[686386.176902] usb 1-1: USB disconnect, device number 62
[686386.177183] pl2303 ttyUSB0: pl2303_set_control_lines - failed: -19
[686386.177197] pl2303 ttyUSB0: error sending break = -19
[686386.177507] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0
[686386.177555] pl2303 1-1:1.0: device disconnected

I have connected it to J14 header on pins 3,4 and 7 on my board i.e white to 3, green to 4 and black to 7 as mentioned in the Developer Kit.

On the host PC, I am using minicom. I ran sudo minicom, which gave me the error: minicom: cannot open /dev/modem: No such file or directory.

Post that, I ran sudo minicom -D /dev/ttyUSB0, as that was the only difference in ls /dev when I removed or added the cable.

This gave me active terminal like this:

Welcome to minicom 2.7.1
OPTIONS: I18n
Compiled on Dec 23 2019, 02:06:26.
Port /dev/ttyUSB0, 15:13:21
Press CTRL-A Z for help on special keys

I restarted my board, waiting for logs to show up here but I didnā€™t get anything.

The output for dmesg | grep THC on the board is:

[ 1.542048] 3100000.serial: ttyTHS0 at MMIO 0x3100000 (irq = 47, base_baud = 0) is a TEGRA_UART
[ 1.543422] 3110000.serial: ttyTHS1 at MMIO 0x3110000 (irq = 48, base_baud = 0) is a TEGRA_UART
[ 1.544422] 3140000.serial: ttyTHS4 at MMIO 0x3140000 (irq = 49, base_baud = 0) is a TEGRA_UART

This is the result of ls /dev/tty* on my host PC:

/dev/tty /dev/tty17 /dev/tty26 /dev/tty35 /dev/tty44 /dev/tty53 /dev/tty62 /dev/ttyS11 /dev/ttyS20 /dev/ttyS3
/dev/tty0 /dev/tty18 /dev/tty27 /dev/tty36 /dev/tty45 /dev/tty54 /dev/tty63 /dev/ttyS12 /dev/ttyS21 /dev/ttyS30
/dev/tty1 /dev/tty19 /dev/tty28 /dev/tty37 /dev/tty46 /dev/tty55 /dev/tty7 /dev/ttyS13 /dev/ttyS22 /dev/ttyS31
/dev/tty10 /dev/tty2 /dev/tty29 /dev/tty38 /dev/tty47 /dev/tty56 /dev/tty8 /dev/ttyS14 /dev/ttyS23 /dev/ttyS4
/dev/tty11 /dev/tty20 /dev/tty3 /dev/tty39 /dev/tty48 /dev/tty57 /dev/tty9 /dev/ttyS15 /dev/ttyS24 /dev/ttyS5
/dev/tty12 /dev/tty21 /dev/tty30 /dev/tty4 /dev/tty49 /dev/tty58 /dev/ttyACM0 /dev/ttyS16 /dev/ttyS25 /dev/ttyS6
/dev/tty13 /dev/tty22 /dev/tty31 /dev/tty40 /dev/tty5 /dev/tty59 /dev/ttyprintk /dev/ttyS17 /dev/ttyS26 /dev/ttyS7
/dev/tty14 /dev/tty23 /dev/tty32 /dev/tty41 /dev/tty50 /dev/tty6 /dev/ttyS0 /dev/ttyS18 /dev/ttyS27 /dev/ttyS8
/dev/tty15 /dev/tty24 /dev/tty33 /dev/tty42 /dev/tty51 /dev/tty60 /dev/ttyS1 /dev/ttyS19 /dev/ttyS28 /dev/ttyS9
/dev/tty16 /dev/tty25 /dev/tty34 /dev/tty43 /dev/tty52 /dev/tty61 /dev/ttyS10 /dev/ttyS2 /dev/ttyS29 /dev/ttyUSB0

Is there anything else I should be doing?

I also tried removing ā€˜quietā€™ from /boot/extlinux/extlinux.conf as mentioned in some issue, but itā€™s still not giving me any output on the host PC.

Any help would be greatly appreciated.

2

Hi,

Please make sure you are using the correct baud rate. Also, I donā€™t quite understand that you said there is no log on your minicom, then where did you dump those dmesg logs?

3

Thanks for the reply.

Please make sure you are using the correct baud rate.

I checked the baud rate on minicom and this is what I found:

Serial device: /dev/ttyUSB0
Lockfile location: /var/lock
Bps/Par/Bits: 115200 8N1

So I suppose the baud rate being used is 115200 bps. Is this not the correct baud rate? I saw the answer by Jerry here, which mentioned the use of picocom -b 115200 /dev/ttyUSBx, so I thought the baud rate was correct.

Also, I donā€™t quite understand that you said there is no log on your minicom, then where did you dump those dmesg logs?

Apologies if it wasnā€™t clear. Iā€™ve already flashed the Xavier NX board with an OS, I ran dmesg | grep THC on the board to get the above mentioned output.

I also ran dmesg | grep Prolific on the host machine and Iā€™ve shared that output above as well.

Iā€™m actually trying to see the bootloader logs to see if my Trusted Application is working or not. (as mentioned here - I want to see where do I get these logs)

4

My question is where did you run ā€œdmesgā€? Is it also from the uart console?

5

Never mind, I was able to get the logs. From your link, I realised that my white and green wires were exchanged on the board due to which I wasnā€™t receiving any data. The guide clearly mentions how do we connect a UART cable to get the required kernel logs.

Thanks a lot for your help!

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