A project about building an operating system for the Raspberry Pi 4B. The base for this project is the following tutorial: https://github.com/s-matyukevich/raspberry-pi-os.git
Plug the black wires of each serial cable onto a Ground pin on the Pi (for example pin 6 and 14).
Then the white wire of one cable to 8 (GPIO 14 / TXD)
Then the green wire of the other cable to 10 (GPIO 15 / RXD)
The serial cable with the white wire connected is transmitting to the computer and has to be plugged into the computer first. It has to show up as /dev/ttyUSB0.
The green wire is the one receiving on the Raspberry Pi and has to be /dev/ttyUSB1.
You can read the Pi's output from the white cable by executing make screen.
Which launches screen, connected to the serial port. However due to its
blocking nature we have to give it a separate cable.
If you have installed picocom or minicom as an alternative to screen then you
actually only need one serial cable of which you can then connect both the
green and the white wire. make screen will then prioritize them over
screen.
Under the assumption that the serial cable is starting with the name
usbserial-. The cable with the highest value is receiving from the Raspberry
Pi and the cable with the smallest value is transmitting to the Raspberry Pi.
For example /dev/cu.usbserial-14320 is used for receiving from the Raspberry Pi and /dev/cu.usbserial-14330 is used for transmitting to the Raspberry Pi.
To make mounting of the SD card in the makefile work it is currently required to have set up the SD card in /etc/fstab to mount in the mnt directory at the project directory root level.
An example config line would be:
# /dev/mmcblk0p1
UUID=7616-4FD8 /home/kjell/git/rose/mnt vfat noauto,nofail,noatime,user,rw 0 2
make flash mounts the SD card, copies the chainloader onto its boot partition and then unmounts it again.
The chainloader uses the STATUS led
and the POWER led
to indicate its current status.
Read as follows:
---> Raspberry is off
---> Chainloader makes space. Shouldn't take long. If you see this, your chainloader may be stuck
Once the Chainloader is waiting for the kernel size () you can build and load the image onto the Raspberry Pi with
make send.
If you already loaded and booted the system you can restart the Pi, to start the chainloader again and rebuild + send the new image, with make resend.
! Note: if you use make resend while the pi is waiting for the make send the Pi will freeze !
If the Pi freezes for this or any other reason you will need to power cycle it and use make send again.