Using GNU Toolchain to Debug Applications on EM Starter Kit


Toolchain for Linux and Windows hosts can be downloaded from the GNU Toolchain Releases page. For Linux hosts there is a choice between complete tarballs that include toolchain, IDE and OpenOCD (like installer for Windows), and tarballs that include toolchain only.

In order to use OpenOCD on Windows it is required to install appropriate WinUSB drivers, see How to Use OpenOCD on Windows for details.

Building an application

To learn how to build and debug application with Eclipse IDE, please use ARC GNU IDE manual.

Different core templates in EM Starter Kit use different memory maps, so different memory map files are required to compile applications that work properly on those configurations. This “toolchain” repository includes memory maps for all supported EM Starter Kit versions and configurations. They can be found at Memory map files in that directory have .x extension and file to be used should be renamed to memory.x, because arcv2elfx linker emulation doesn’t support ability to override that file name. Please refer to Linker scripts and memory.x files for more details about memory.x files.

For example for EM Starter Kit v2.3 EM7D to build an application:

$ cp -a toolchain/extras/dev_systems/sk2.3_em7d.x memory.x
$ arc-elf32-gcc -Wl,-marcv2elfx --specs=nosys.specs -mcpu=em4_dmips -O2 -g \
     test.c -o test.elf
List of compiler flags corresponding to particular CPUs
v1 EM4 -mcpu=em4_dmips -mmpy-option=wlh5
EM6 -mcpu=em4_dmips -mmpy-option=wlh5
v2.0 EM5D -mcpu=em4 -mswap -mnorm -mmpy-option=wlh3 -mbarrel-shifter
EM7D -mcpu=em4 -mswap -mnorm -mmpy-option=wlh3 -mbarrel-shifter
EM7DFPU -mcpu=em4 -mswap -mnorm -mmpy-option=wlh3 -mbarrel-shifter -mfpu=fpuda_all
v2.1 EM5D -mcpu=em4_dmips -mmpy-option=wlh3
EM7D -mcpu=em4_dmips -mmpy-option=wlh3
EM7DFPU -mcpu=em4_fpuda -mmpy-option=wlh3
v2.2 EM7D -mcpu=em4_dmips
EM9D -mcpu=em4_fpus -mfpu=fpus_all
EM11D -mcpu=em4_fpuda -mfpu=fpuda_all
v2.3 EM7D -mcpu=em4_dmips
EM9D -mcpu=em4_fpus -mfpu=fpus_all
EM11D -mcpu=em4_fpuda -mfpu=fpuda_all

C library for GNU Toolchain for ARC provides basic support for UART module of EM Starter Kit, which allows to use standard C function for input and output: printf(), scanf(), etc. Memory map files are also provided for processor configurations of EM Starter Kit. Both of those features are available via special “specs” files: emsk_em9d.specs and emsk_em11d.specs (there is no separate file for EM7D of EM Starter Kit, it is identical to EM9D). Usage example is following:

$ cat hello_world.c
#include <stdio.h>
int main() {
    printf("hello world\n");
    return 0;

$ arc-elf32-gcc --specs=emsk_em9d.specs -mcpu=em4_dmips hello_world.c

Note that it is still required to specify valid -mcpu option value - it is not set by the specs file.

Running an application with OpenOCD

Starting OpenOCD

Parameters of a particular target board are described in the OpenOCD configuration files. OpenOCD repository from Synopsys already includes several configuration files made specifically for Synopsys own development platforms: ARC EM Starter Kit and ARC SDP. Due to differences between different versions of ARC EM Starter Kit hardware, there are separate configuration files for different ARC EM Starter Kit versions:

  • snps_em_sk_v1.cfg - for ARC EM Starter Kit v1.x.
  • snps_em_sk_v2.1.cfg - for ARC EM Starter Kit versions 2.0 and 2.1.
  • snps_em_sk_v2.2.cfg - for ARC EM Starter Kit version 2.2.
  • snps_em_sk_v2.3.cfg - for ARC EM Starter Kit version 2.3.
  • snps_em_sk.cfg - this is a configuration for ARC EM Starter Kit 2.0 and 2.1, preserved for compatibility.

Following documentation would assume the usage of the latest ARC EM Starter Kit version 2.3 which is similar to 2.2.

Start OpenOCD:

# On Linux (for manually built OpenOCD):
$ openocd  -c 'gdb_port 49101' -f board/snps_em_sk_v2.3.cfg

# On Linux (for prebuilt OpenOCD from IDE package):
$ $ide_dir/bin/openocd -s $ide_dir/share/openocd/scripts \
    -c 'gdb_port 49101' -f board/snps_em_sk_v2.3.cfg

@rem on Windows:
> openocd -s C:\arc_gnu\share\openocd\scripts -c "gdb_port 49101" ^
  -f board\snps_em_sk_v2.3.cfg

OpenOCD will be waiting for GDB connections on TCP port specified as an argument to gdb_port command, in this example it is 49101. When gdb_port command hasn’t been specified, OpenOCD will use its default port, which is 3333, however this port might be already occupied by some other software. In our experience we had a case, where port 3333 has been occupied, however no error messages has been printed but OpenOCD and GDB wasn’t printing anything useful as well, instead it was just printing some ambiguous error messages after timeout. In that case another application was occupying TCP port only on localhost address, thus OpenOCD was able to start listening on other IP addresses of system, and it was possible to connect GDB to it using that another IP address. Thus it is recommended to use TCP ports which are unlikely to be used by anything, like 49001-49150, which are not assigned to any application.

OpenOCD can be closed by CTRL+C. It is also possible to start OpenOCD from Eclipse as an external application.

Connecting GDB to OpenOCD

Write a sample application:

 /* simple.c */
 int main(void) {
     int a, b, c;
     a = 1;
     b = 2;
     c = a + b;
     return c;

Compile it - refer to “Building application” section for details, creation of memory.x is not shown in this example:

$ arc-elf32-gcc -Wl,-marcv2elfx --specs=nosys.specs -mcpu=em4_dmips -O2 -g \
    simple.c -o simple_sk2.3_em7d.elf

Start GDB, connect to target and run it:

$ arc-elf32-gdb --quiet simple_sk2.1_em5d.elf
# Connect. Replace 3333 with port of your choice if you changed it when starting OpenOCD
(gdb) target remote :3333
# Increase timeout, because OpenOCD sometimes can be slow
(gdb) set remotetimeout 15
# Load application into target
(gdb) load
# Go to start of main function
(gdb) tbreak main
(gdb) continue
# Resume with usual GDB commands
(gdb) step
(gdb) next
# Go to end of the application
(gdb) tbreak exit
(gdb) continue
# For example, check exit code of application
(gdb) info reg r0

Execution should stop at function exit. Value of register r0 should be 3.

Known issues and limitations

  • Out of the box it is impossible to perform any input/output operations, like printf, scanf, file IO, etc.

    • When using an nSIM hostlink (GCC option --specs=nsim.specs), calling any of those function in application will result in a hang (unhandled system call to be exact).
    • When using libnosys (--specs=nosys.specs), standard IO functions will simply do nothing - they will set errno = ENOSYS and return -1 at most.
    • It is possible to use UART for text console I/O operations, but that is not implemented by default in GNU toolchain. Consult EM Starter Kit documentation and examples for details.
  • Bare metal applications has nowhere to exit, and default implementation of exit is an infinite loop. To catch exit from application you should set breakpoint at function exit like in the example.