Advice on JTAG debugging RTEMS for ARM (beaglebone)

[Chris Johns]

On 29/12/20 9:27 am, James Fitzsimons wrote:
> Hi all,
> 
> I am trying to debug an RTEMS application on a TI AM3358 ARM processor
> (Beaglebone Black) and the RTEMS startup code is halting on the bsp_fdt_get call.
> 
> I'm using TI Code Composer Studio to load the RTEMS application image via XDS100
> V3.0 debugger. If I reset the program counter and step through the startup code
> I see it error on the bsp_fdt_get() call.

Is this a crash or is an error reported? We should report an error and not crash.

> My IDE isn't copying an fdt image to the expected location the way uboot would,
> and so this makes sense. My question is how do other people get around this problem?
> 
> Has anyone else used a similar setup and solved this issue?

I have not hit this issue but I saw this as a problem with the approach taken of
loading an FDT via the bootloader. It would have been nice to have a way to
integrate an FDT into the IMFS (or executable) rather than an external load.

> Many thanks for any advice you can provide.

The only approaches I can think of are a bit hack'ish but they might work.

Can you set up an environment to load and run uboot from an SD card? Have uboot
load the FDT then stop at it's command line. Once at the command line connect
via JTAG and load the application. I suspect you will need to set the registers
to the same values uboot uses when entering the application. I seem to remember
one of them points to the FDT blob.

Another approach is to boot using uboot and have it load the FDT and RTEMS
executable then jump to it. If you can connect via JTAG, reset the processor,
set a hardware break point on the entry point to RTEMS, and start the processor
running from reset it should trigger when uboot jumps to RTEMS. The entry point
is at a fixed address. When the breakpoint is hit delete it and then you can set
further break points in your application.

Chris