Using Ashling Opella-XD GDB server with AXS SDP

Note

The Ashling GDB Server software for ARC is implemented by Ashling and delivered as part of the Ashling Opella-XD probe for ARC processors product. This guide aims to provide all necessary information to successfully debug ARC applications using the GNU toolchain for ARC and the Ashling GDB server, however for all issues related to the Ashling GDB Server application, user should contact Ashling Microsystems Ltd. for further assistance.

Ashling GDB Server can be used to debug application running on the AXS10x family of software development platforms. It is recommended to use latest version of Ashling drivers and software package available.

Building an application

To learn how to build applications for AXS SDP, please refer to corresponding section of OpenOCD manual.

Board configuration

Board should be configured mostly the same way as for the OpenOCD, but it is required to change JP1402 and JP1403 jumpers - to debug with Opella-XD it is required to set JP1403 and unset JP1402, while for OpenOCD it is otherwise. Refer to OpenOCD manual and to the User Guide of the AXC00x CPU card you are using for more details.

Running Ashling GDB Server

Options of the Ashling GDB Server are described in its User Manual. It is highly recommended that users be familiar with Ashling GDB Server operation before proceeding. In a nutshell, to run GDB Server with multiple cores in the JTAG chain:

$ ./ash-arc-gdb-server --device arc --arc-reg-file <ARC_REG_FILE> \
    --scan-file arc2core.xml  --tap-number 1,2

That will open GDB server connections on port 2331 (core 1) and 2332 (core 2). Use GDB to connect to the core you want to debug. <ARC_REG_FILE> is a path to a file with AUX register definitions for the core you are going to debug. Actual file that should be used depends on what target core is. A set of files can be found in this toolchain repository in extras/opella-xd directory. In this directory there are arc600-cpu.xml, arc700-cpu.xml, arc-em-cpu.xml and arc-hs-cpu.xml files for GDB server, direct link.

To run with AXS101 with all four cores in a chain:

$ ./ash-arc-gdb-server --device arc --arc-reg-file <ARC_REG_FILE> \
    --scan-file arc4core.xml  --tap-number 1,2,3,4

File arc4core.xml is not shipped with Ashling GDB Server, but can be easily created after looking at arc2core.xml and reading Ashling Opella-XD User Manual.

To run Ashling GDB Server with JTAG chain of a single core:

$ ./ash-arc-gdb-server --device arc --arc-reg-file <ARC_REG_FILE>

Option --jtag-frequency ...MHz can be passed to gdbserver to change JTAG frequency from default 1MHz. Rule of the thumb is that maximum frequency can be no bigger than half of the frequency, but for cores with external memory that value can be much lower. Most of the cores in different SDP models can work safely with JTAG frequencies around 10 ~ 12 MHz. ARC EM6 in the AXS101 is an exception - maximum recommended frequency is 5MHz.

Running GDB

Run GDB:

$ arc-elf32-gdb ./application.to.debug

Then it is required to specify description of target core that will be debugged with Ashling GDB Server.

Then it is required to specify XML target description file appropriate for the ARC_REG_FILE used to start Ashling GDB server. XML target description files for arc600-cpu.xml, arc700-cpu.xml, arc-em-cpu.xml and arc-hs-cpu.xml can be found in this toolchain repository in extras/opella-xd, direct link. Provided files are: opella-arc600-tdesc.xml, opella-arc700-tdesc.xml, opella-arcem-tdesc.xml and opella-archs-tdesc.xml. It is important that ARC_REG_FILE for Ashling GDB server and target description file for GDB match to each other, so if Opella’s file has been modified, so should be the target description. Also due to incompatible changes in GDB, it is required to disable GDB p/P remote packet.:

(gdb) set tdesc filename <path/to/opella-CPU-tdesc.xml>

Connect to the target GDB server:

(gdb) target remote <gdbserver-host>:<port-number>

where <gdbserver-host> is a hostname/IP-address of the host that runs OpenOCD (can be omitted if it is localhost), and <port-number> is a number of port of the core you want to debug (see previous section).

In most cases you need to load application into the target:

(gdb) load

The system is now ready to debug the application.

To debug several cores on the AXC00x card simultaneously, start additional GDBs and connect to the required TCP ports. Cores are controlled independently from each other.

Known issues

  • XML register file is specified only once in the GDB Server argument, that means that if your JTAG chain includes multiple cores of different model (e.g. ARC 700 and EM) you cannot debug them simultaneously, but you can debug multiple cores of they same type (e.g. all EM).
  • HS36 core of the AXS102 cannot be used when both cores are in the JTAG chain - if “resume” operation is initiated on the core, GDB Server and GDB will behave like it is running and never halting, but in reality it never started to run. To workaround this issue remove HS34 from the JTAG chain (remove JP1200 jumper on the AXC002 card, remove --scan-file and --tap-number options from Ashling GDB Server command line). If you need both HS34 and HS36 in the JTAG chain use OpenOCD instead of Ashling GDB Server. Why this problem happens is a mystery, since HS36 works without problems when it is single in the JTAG chain, and HS34 always work fine; this is likely a problem with Ashling GDB Server.
  • In Opella software version of 1.0.6 prior to 1.0.6-D it has been observed that in some cases target core may hang on application load, if target has external memory attached. This happens when P-packet is disabled, and since P-packet should be disabled when using new GDB with those versions of Opella software, effectively it is not possible to use GDB >= 7.9 with Ashling GDBserver < 1.0.6-D to debug cores that employ external memory.
  • In version of 1.0.6 it has been observed that breakpoint set at main() function of application may be not hit on first run in HS34 core in AXS102.
  • In version 1.0.6-D it has been observed that gdbserver doesn’t invalidate I$ of the second ARC 600 core of AXS101 - if this core hits a software breakpoint it gets stuck at it forever.

Known Issues of previous versions of Ashling software

  • In version of Ashling software up to 1.0.5B, passing option --tap-number 2 will cause GDB Server to print that it opened connection on port 2331 for core 2, however that is not true, instead GDB Server will create this connection for core 1. Therefore if your JTAG chain contains multiple ARC TAPs you _must_ specify all of them in the argument to --tap-number option.

  • Up to version 1.0.5F there is an error in handling of 4-byte software breakpoints at 2-byte aligned addresses. For example in this sample of code attempt to set breakpoint at 0x2b2 will fail.:

    0x000002b0 <+0>:    push_s     blink
    0x000002b2 <+2>:    st.a       fp,[sp,-4]
    0x000002b6 <+6>:    mov_s      fp,sp
    0x000002b8 <+8>:    sub_s      sp,sp,16
    
  • Big endian ARC v2 cores are not supported on versions prior to 1.0.5-F.