Debug using Serial Debug Cable about rust-raspberrypi-os-tutorials

[andre-richter]

As @rahealy already pointed out, this is currently not possible.

While it would be possible to come up with a software solution, e.g. implementing a GDB Remote Serial Protocol server in an EL > EL1, this is unfortunately out of the scope for now.

It would be a fun project, but given that JTAG adapters are quite affordable, not worth pursuing in light of the effort that would be needed.

[rahealy]

Yes. https://github.com/rust-embedded/rust-raspi3-OS-tutorials#-usb-serial-output

[vinaychandra]

That is useful to do booting via USB. My question was regarding debugging using GDB.

[rahealy]

AFAIK the RPi's JTAG is implemented at the transistor level in the hardware. As a result JTAG requires a JTAG adapter - either built from plans found on the internet and/or hacked together and/or purchased from a dealer like Olimex.

You also might consider emulation using the qemu target in the tutorial's Makefile. Please see this comment #45 (comment) for an example of how to modify the 12_cpu_exceptions_part1 tutorial to connect an instance of gdb-multiarch to qemu running in the docker image provided by the tutorial's author @andre-richter.

If you have questions about my alterations to 12_cpu_exceptions_part1 please feel free to ask in the comments section of the commit.

[rahealy]

@vinaychandra Forgot to mention: The reason I answered yes to your original question is that your programs can read/write to the RPi UART and send debug info over the serial->USB converter to a computer running a terminal emulator like PuTTY.

[vinaychandra]

Thanks for the info! Yes, while I do understand that we can send random debug info over UART, I am looking more for gdb support over USB so that breakpoints and watches would work. I also do understand that qemu is an option, but I wanted to see if it is possible to do breakpoint debugging over USB/UART

[rahealy]

@vinaychandra I did some research. The Arm® Architecture Reference Manual
Armv8, for Armv8-A architecture profile chapter D2 AArch64 Self-hosted Debug describes the hardware debugging goodies for the ARM cores on the RPi3 SoC. So it might be possible. Has anyone written a crate that you can just add as a dependency and begin debugging? I don't know.

[andre-richter]

Closing for now since this feature is not on the agenda for the near future.