EmbExp-ProgPlat - embedded experiment program platform

This repository provides a rudimentary bare-metal execution environment that can be flexibly used for multiple architectures and boards. Is is easy to extend and only assumes a board connection in terms of a GDB server and UART interface.

Extending the platform for new boards requires a linkerscript, entry code, a UART driver and possibly GDB scripts to get the code loaded correctly. The main goal is conducting low-level experiments that are typically implemented for a certain processor ISA (architecture family).

This platform mainly makes use of the EmbExp-Box infrastructure to run the low-level experiment software on hardware boards. It is fairly integrated with this infrastructure for convenience but can also be used with other GDB server based setups with a few tweaks. The repository EmbExp-BalRob is an example where the program platform has been ported to local deployment for one board type. The repository EmbExp-Logs utilizes this platform to run individual experiments and collect their outputs.

Supported targets

• ARM Cortex-A7 - ARMv7-A (Raspberry Pi 2B)
• ARM Cortex-A53 - ARMv8-A (Raspberry Pi 3B)
• ARM Cortex-A72 - ARMv8-A (Raspberry Pi 4B)
• ARM Cortex-M0 - ARMv6-M (LPCXpresso LPC11C24)
• SiFive Freedom E300 - RV32IMAC (Arty A7-100T)

Getting started

Even though the cross compiler can be provided using environment variables, the preferred way is to load a HolBA environment. Fist, look at the repository HolBA to setup a basic environment with the EmbExp repositories as well as the required gcc packages. Then, load the environment by running source ${HOLBA}/env.sh. Finally, test the compilation by compiling everything with the execution of make. Some gdb requires the package libtinfo5 and you may need to install it with apt or similar. If possible, try to see the output of an execution with make connect in one terminal and make runlog in another.

1. Configure

See file Makefile.config and all/inc/config.h.

2. Compile

• Compilation and linking depends on Makefile.config. The directory all/ is always considered and otherwise the configured PROGPLAT_BOARD and PROGPLAT_ARCH selects the respective subdirectories in board/ and arch/. The linker script is taken from board/${PROGPLAT_BOARD}/.
• Compiler options:
  • ARM compiler: "gcc_arm" and "gcc_arm8" from HolBA (preferred)
  • Arch package aarch64-linux-gnu
• Run make.

3. Connect to experiment platform (using EmbExp-Box)

1. Run make connect. This runs {EmbExp-Box}/interface/remote.py ${PROGPLAT_BOARD}.
2. Wait until openocd is started and the local ports are connected (20000-UART 20013-gdb and 20004-oocd_telnet).
3. Leave the terminal running until you're done.
4. Don't forget to disconnect afterwards by pressing return in this terminal (so that the board is free for others again).
5. Just in case: If one of the applications crashes by some operation (like openocd), just stop the script by pressing return and start everything again.

4. Running an experiment

• Run make runlog and observe the output.

More advanced debugging

1. Connecting to the UART

• If it suffices, just run make log,
• otherwise:
  1. Run make uart.
  2. Press the key combination ^] (Ctrl+]).
  3. Type mode character and hit return.

2. Running/debugging the program.

• Run with make run, or
• debug with make debug.

3. Starting GDB with gdb-dashboard

1. Install gdb-dashboard by wget -P ~ git.io/.gdbinit (from https://github.com/cyrus-and/gdb-dashboard).
2. Run gdb by make debug.
3. Start another terminal and run tty to determine this shell's identifier.
4. In the gdb shell, type dashboard source -output /dev/pts/3 where /dev/pts/3 is the shell identifier determined before.

4. Debugging examples with GDB

• j main jumps to the symbol main and executes

• when gdb is running and no prompt shows, press the key combination ^c (Ctrl+c) to interrupt the execution

• j main.c:198 jumps to the beginning of code line 198 and executes

• continue to continue execution

• step to step to the next code line

• stepi to step to the next assembly instruction

• set $pc = 0x1000 and continue to execute from address 0x1000

• b main sets a breakpoint at the symbol main

• clear main clears the breakpoint at the symbol main

• monitor poll to show the underlying processor state rendered by OpenOCD

• some documentation

  • https://sourceware.org/gdb/onlinedocs/gdb/Continuing-and-Stepping.html
  • https://stackoverflow.com/questions/42800801/how-to-use-gdb-to-debug-qemu-with-smp-symmetric-multiple-processors
  • https://quequero.org/2014/04/introduction-to-arm-architecture/