Advice on JTAG debugging RTEMS for ARM (beaglebone)

[Chris Johns]

On 29/12/20 3:24 pm, James Fitzsimons wrote:
> Hi Chris,
> 
> Thanks very much for your reply and advice.
> 
> On Tue, 29 Dec 2020 at 11:58, Chris Johns <chrisj at rtems.org
> <mailto:chrisj at rtems.org>> wrote:
> 
>     > 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.
> 
> 
> Neither - the processor continues running, just not executing anything useful.
> 
>     > 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.
> 
> 
> Agreed - this would make it much easier to debug things. Even just having this
> as an option
> to support debugging would be useful.
>  
> 
>     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.
> 
> 
> Thanks for this suggestion - I've managed to get this working pretty much as you
> described.
> I build the SD card image and boot from that, then connect via JTAG, reset and
> break on Init().
> It's a pretty clunky process, but at least I have actual on device debugging
> working now instead of
> having to rely on printf debugging.

Excellent and thanks for reporting it back to us. Yes it is clunky however
anything else would need time spent adding IMFS support or directly linked in
support and no one has done that.

Chris