GPS Serial Console issue on Ubuntu 20.04 on Raspberry Pi 4

Question

I am trying to use the BerryGPS-IMUv3 (https://ozzmaker.com/berrygps-berrygps-imu-quick-start-guide/) on a RPi 4B running Ubuntu 20.04 headless. When the BerryGPS-IMU is installed, it prevents the pi from booting, presumably because it is streaming data to the pi and interrupting the boot process. The manufacturer's instructions state that the serial console needs to be disabled, but the instructions assume the user is running raspbian.

Has anyone figured out a way to disable the serial console (but keep the serial port enabled) on Ubuntu 20.04? I think I need to set the boot delay to "-2" to ignore interrupts but I'm not sure how to access that setting via ssh.

Answer 1

I had a similar problem, and found this solution to this (tested with a Raspberry Pi 4, Ubuntu 20.04 and an Adafruit Ultimate GPS HAT). As you stated, it is about stopping U-boot from interrupting autoboot when receiving input on the serial lines. Unfortunately, this requires recompilation of the U-boot binary. I performed this on the RPi itself, not with cross-compilation per the link.

My steps were as follows:

1. Install the dependencies: apt-get install git make gcc gcc-aarch64-linux-gnu bison flex (Note I needed to add bison and flex to the packages because the build failed without them, this isn't mentioned in the linked answer)

2. Get the U-boot code base: git clone --depth 1 git://git.denx.de/u-boot.git && cd u-boot/

3. Edit the rip_4_defconfig: vi configs/rpi_4_defconfig adding the lines:

CONFIG_BOOTDELAY=-2
CONFIG_SILENT_CONSOLE=y
CONFIG_SYS_DEVICE_NULLDEV=y
CONFIG_SILENT_CONSOLE_UPDATE_ON_SET=y
CONFIG_SILENT_U_BOOT_ONLY=y
Per the linked post

4. Edit the rpi.h: vi include/configs/rpi.h, amending this stanza to add the "silent=1\0" line

#define CONFIG_EXTRA_ENV_SETTINGS \
    "dhcpuboot=usb start; dhcp u-boot.uimg; bootm\0" \
    "silent=1\0" \
    ENV_DEVICE_SETTINGS \
    ENV_DFU_SETTINGS \
    ENV_MEM_LAYOUT_SETTINGS \
    BOOTENV

5. Then make rpi_4_defconfig && make

6. Relocate the binary output from make:

mv /boot/firmware/uboot_rpi_4.bin /boot/firmware/uboot_rpi_4.bin.bak
mv u-boot.bin /boot/firmware/uboot_rpi_4.bin

7. I think that was everything I did to get my RPi and Adafruit GPS HAT booting with Ubuntu 20.04.

Answer 2

Compiling U-boot did not work for me (as of today, latest Ubuntu 20.04 on Raspberry Pi 4). I had to use the serial console to change the settings. followed this answer: https://askubuntu.com/a/1278181/1569332 Let me try to expand it a bit.

1. U have to connect a serial adopter to the Pi's Tx Rx (GPIO 14,15) pins and log on to the Raspberry Pi's Serial Console (UART) from another computer. refer to this guide for a tutorial on that. I used an Arduino (running the SoftwareSerial example -->> changed the baud rate to 115200) connected like this: connection diagram

   Rpi TXD -- Arduino pin 10

   Rpi RXD -- Arduino pin 11

   Rpi GND -- Arduino GND

2. The pi being powered off, connect the serial device(Arduino) to the other computer, open the Arduino serial monitor (or putty or sudo screen /dev/tty{your port} 115200)

3. Power the Rpi and you should see something similar to the boot screen.

4. Keep pressing ENTER (/any key) on the serial monitor/console and it should print:

   Hit any key to stop autoboot: 2 0

   U-Boot>

If u missed the U-Boot menu, u would be prompted to log in. Repeat steps 3 and 4 quickly.

5. Enter the following commands:

   setenv bootdelay -2

   saveenv The response should be Saving Environment to FAT... OK

Reboot to verify.