Running NuttX

Embedded boards have different ways to get your program onto them and get them running. This guide assumes your board has a JTAG connector, and you have a JTAG hardware debugger like a Segger J-Link. JTAG is a set of standards that let you attach a hardware device to your embedded board, and then remotely control the CPU. You can load code, start, stop, step through the program, and examine variables and memory.

  1. Attach the Debugger Cables

  2. Start the Debugger

    Refer to your JTAG debugger’s documentation for information on how to start a GDB Server process that gdb can communicate with to load code and start, stop, and step the embedded board’s CPU. Your command line may be different from this one.

    $ JLinkGDBServer -device ATSAMA5D27 -if JTAG -speed 1000 -JTAGConf -1,-1
  3. Launch the Gnu Debugger

    In another terminal window, launch the GDB for your platform. In the case of this guide, this came with the ARM Embedded Gnu Toolchain we downloaded in the Install step.

    $ arm-none-eabi-gdb
  4. Connect to the board’s serial console

    Usually you connect a USB-to-serial adapter to the board’s serial console so you can see debug logging or execute Apache NuttX Shell (nsh) commands. You can access the serial console from Linux with the picocom terminal program. From another terminal, do this:

    $ picocom -b 115200 /dev/ttyUSB0
  5. Set gdb to talk with the J-Link

    (gdb) target extended-remote :2331
  6. Reset the board

    (gdb) mon reset
  7. Stop the U-boot bootloader after board setup is complete

    Switch to the serial console to press the <Space> key to stop the U-Boot bootloader from booting NuttX. You need to boot to this point so U-Boot can set up the SAMA5D27C’s memory mapping.

  8. Halt the bootloader

    (gdb) mon halt
  9. Load nuttx debugging symbols:

    (gdb) file nuttx
  10. Load nuttx

    (gdb) load nuttx
    `/home/adamf/src/nuttx-sama5d36-xplained/nuttx/nuttx' has changed; re-reading symbols.
    Loading section .text, size 0x9eae4 lma 0x20008000
    Loading section .ARM.exidx, size 0x8 lma 0x200a6ae4
    Loading section .data, size 0x125c lma 0x200a6aec
    Start address 0x20008040, load size 654664
    Transfer rate: 75 KB/sec, 15587 bytes/write.
  11. Set a breakpoint

    (gdb) breakpoint nsh_main
  12. Start nuttx

    (gdb) continue
    Breakpoint 1, nsh_main (argc=1, argv=0x200ddfac) at nsh_main.c:208
    208        sched_getparam(0, &param);
    (gdb) continue

Restarting NuttX after making changes

If you make changes to NuttX or the applications, you need to reload and restart NuttX.

You can stop NuttX by typing <Control-C> in the gdb window. Then all you have to do is steps 8 (halt), 10 (load), and 12 (continue).

Debugging Shortcuts

Note that you can abbreviate gdb commands, info b is a shortcut for information breakpoints; c works the same as continue, etc.

Next: Configuring NuttX