serial_rpi4.txt

Debugging serial in a raspberry pi 4


vcgencmd bootloader_config

#Export config file

cp /lib/firmware/raspberrypi/bootloader/beta/pieeprom-2019-09-10.bin pieeprom.bin
rpi-eeprom-config pieeprom.bin > bootconf.txt

vi bootconf.txt

# Example change. If you have a UART cable then setting BOOT_UART=1 will help debug boot issues
BOOT_UART=1

#Create the binary
rpi-eeprom-config --out pieeprom-new.bin --config bootconf.txt pieeprom.bin

#Flash the new eeprom && reboot

sudo rpi-eeprom-update -d -f ./pieeprom-new.bin
sudo reboot


updating the on board flash

Source:
https://www.raspberrypi.org/documentation/hardware/raspberrypi/booteeprom.md
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711_bootloader_config.md

The correct use of a serial port is then /dev/Serial0

root@rpib42g:~# ls -l /dev/serial*
lrwxrwxrwx 1 root root 5 Jan 25 22:22 /dev/serial0 -> ttyS0
lrwxrwxrwx 1 root root 7 Jan 25 22:22 /dev/serial1 -> ttyAMA0

Test if the ports are GPIO or Serial

root@rpib42g:~# raspi-gpio get 14-15
GPIO 14: level=1 fsel=2 alt=5 func=TXD1 pull=NONE
GPIO 15: level=1 fsel=2 alt=5 func=RXD1 pull=UP

These are serial.

J8:
   3V3  (1) (2)  5V    
 GPIO2  (3) (4)  5V    
 GPIO3  (5) (6)  GND   
 GPIO4  (7) (8)  GPIO14 (TXD)
   GND  (9) (10) GPIO15 (RXD)