DS-5 Snapshot Viewer Enhancements

In DS-5 v5.21 Snapshot Viewer has been improved, with additional functionality and better ease of use. This release extends support to include ARM®v8 architecture, all core registers plus peripheral SFRs, multiple memory spaces, and Linux Kernel or Device Driver debug. The viewer is now data-driven, removing the need to hand-script new platform configurations.

Offline debug and trace

Sometimes, it’s not possible to use a conventional debug and trace session (through a JTAG debug and trace unit) to investigate a problem. There are a number of scenarios where JTAG debug can’t be used:

• The problem that you need to investigate was seen on production hardware, that doesn’t have debug connectors. At best, this means that you have to re-create the problem on development hardware with full JTAG debug and trace capabilities
• Some problems can’t be replicated with a debugger connected. The problems may be rare and occur infrequently, or you might only be able to re-create the problems out in the field, under particular customer use-cases, where it’s impractical to connect a debugger
• You might have restricted access to development hardware, this is particularly true during SoC bring-up and with first revisions of development hardware. Although it might be easy to re-create the problem, scheduling time for investigation is more challenging
• You need to investigate a crash, hang, or lock-up. Under these situations JTAG debug may be compromised, and information available to a debugger may be limited. If you reset the target to restore debug capabilities, you will almost certainly lose useful information about the cause of the crash

DS-5 Snapshot Viewer

In these situations you need a debugger that can help you analyse any information that could be dumped from the target (including register values, memory contents, and trace data) without the need to connect to the target itself. The ARM® DS-5 Debugger provides a Snapshot Viewer which takes information from dump files rather than from a target via a JTAG debug session. The Snapshot Viewer provides the same register, memory, disassembly, variable, and trace views as you would see in a JTAG debug and trace session, up to the limits of the information contained in the dump files. No target or JTAG unit are needed, and symbol information (including source code linking) can be used as normal. Since you’re not connected to a target, it’s not possible to make changes in the target state (including run-control operations) – you are debugging a snapshot of the target’s state.

The ARM DS-5 Snapshot Viewer is often used with CoreSight™ Access Library. This is an open source library that can run under a Linux kernel, and provides a high-level API for control of CoreSight debug and trace components. The library can be used to configure CoreSight trace when no debugger can be connected, and then store the captured trace, with memory and register contents, where they can be recovered for off-line analysis in a debugger (on an SD card perhaps). A number of example configurations for common platforms are shipped with DS-5, and it’s easy to adapt and extend these sample configurations to give support for your own target hardware.

Enhancements for DS-5 v5.21

In DS-5 v5.20, Snapshot Viewer was a proof of concept which gave only initial functionality. Because of the large amount of interest in the DS-5 Snapshot Viewer, and the large number of customer use-cases, in DS-5 v5.21 the Snapshot Viewer has been substantially enhanced. In DS-5 v5.21 the Snapshot Viewer offers a much wider range of functionality:

• Support has been extended to include ARMv8 architecture cores (ARM®Cortex®-A53, ARM®Cortex®-A57, ARM®Cortex®-A72). Previously, only ARMv7 architecture cores were supported
• In DS-5 v5.20, core register support was limited to critical registers only (R0-R15). Register support has been extended in DS-5 v5.21 to include all core registers, plus peripheral SFRs
• In previous releases of DS-5, Snapshot Viewer only provided support for a single memory space. This meant that Secure, Non-Secure, and Physical (for example) memory addresses could not be distinguished in Snapshot Viewer, and only one value could be displayed for each memory address. In DS-5 v5.21, Snapshot Viewer support has been extended to cover multiple memory spaces
• Support has been added for Linux Kernel and Device Driver debug operations. Note that the memory dumps used by Snapshot Viewer need to contain the necessary memory contents – such as kernel data structures
• In DS-5 v5.20, a new DS-5 platform configuration was needed for each target platform. A small number of sample platform configurations were shipped with DS-5, and although these could be used as a basis for a new platform configuration, virtually every new platform would require some hand scripting. The scripting API is simple and easy to use, but it’s not an area where many users have extensive experience – and this could make it difficult to add support for new platforms. In DS-5 v5.21, the necessity for new platform configurations (and therefore, all hand scripting) has been removed. A single Snapshot Viewer platform configuration is shipped with DS-5, and it is capable of using a snapshot from any target. Information such as number and type of core is now taken from the snapshot dump files
• The CoreSight Access Library examples have been extended in line with the extensions to Snapshot Viewer. A new example configuration has been added for the ARM Juno reference platform (Cortex-A57 and Cortex-A53), and the existing examples have been extended to use the new Snapshot Viewer dump file formats (adding information about core type and number)

If you have any questions, feel free to post them below. Also get in touch if you use the Snapshot Viewer, we’d love to hear feedback on how it works for you.