Overview

In a typical development environment the SAMA5D3x-MB board is programmed via a JTAG/SWD interface. This will either be by loading smaller applications into the on-chip SRAM, or into suitably initialised DDR2-SDRAM memory. Alternatively applications may be loaded into bootable memory-mapped devices, e.g. EBI_CS0 NOR flash, or loaded via the on-chip RomBOOT code via a second-level SRAM boot scheme. The following sections initially deal with JTAG/SWD hardware based debugging approaches.

For debugging applications are loaded and then executed on the board via the debugger arm-eabi-gdb, or via the Eclipse IDE.

The SAMA5D3x-MB motherboard provides a built-in J-Link hardware debug solution, as well as optionally providing the J9 JTAG connector for attaching 3rd-party hardware debuggers (e.g. Ronetix PEEDI).

J-Link

By default the motherboard provides access to both the SAMA5's DBGU (debug UART) and the J-Link adapter through the J14 USB connector. Output on the DBGU channel is accessible via USB on a connected host as a USB CDC-ACM serial class device. Additionally, debugging support is accessible through the proprietary J-Link adaptor via the Segger J-Link GDB server.

The motherboard can be modified (by adding and removing resistors) to route DBGU to the J8 USART1 connector. However, if diagnostics via that connector are desired, it is simpler to re-configure eCos to directly send diagnostics to the J8 port. This can be achieved by setting the HAL diagnostic console channel (and if using RedBoot, GDB channel) to port 1 (the default setting of 0 indicates routing to the DBGU). However, if it is necessary after all to modify the hardware and route DBGU to J8, then support for the SAMA5's USART1 device must be manually disabled by the user as it will no longer be physically connected (removing the "implements CYGINT_HAL_ARM_CORTEXA_SAMA5D3_USART1" line from hal_arm_cortexa_sama5d3x_mb.cdl).

JLinkGDBServer

Segger's JLinkGDBServer application provides a network-based GDB server connection to J-Link hardware debuggers, including on-board J-Link hardware as used on the SAMA5D3x-MB. The Segger webpage http://www.segger.com/jlink-software.html provides a J-Link software package download that incorporates the J-link GDB Server.

Note

When downloading the software you may need to click on a link “I do not have a serial number because I own an eval board with J-Link on-board. How can I download J-Link software for it?”. This will allow you to download the J-Link software without prior knowledge of a serial number. Experience has also shown that a reboot of the PC may be required after installation of the jlink software. To ensure compatibility between the on-board J-Link firmware and software, agree to any prompt you may encounter to update the firmware during the first run of the J-Link software.

A helper script sama5d3xek-ddram.jlink is provided in the misc directory of the sama5d3x_mb package. This should be specified when executing the JLinkGDBServer application, and implements a set of commands that are executed when a GDB connection is established to the server. For example, under Linux:

$ JLinkGDBServer -device ATSAMA5D31 -xc $ECOS_REPOSITORY/packages/hal/arm/cortexa/sama5d3/sama5d3x_mb/current/misc/sama5d3xek-ddram.jlink

Under Windows:

C:\eCosPro> "C:\Program Files (x86)\SEGGER\JLink_V612j\JLinkGDBServerCL.exe" -device ATSAMA5D31 -xc $ECOS_REPOSITORY\packages\hal\arm\cortexa\sama5d3\sama5d3x_mb\<vsn>\misc\sama5d3xek-ddram.jlink

Note that in the above examples the -device argument should reference the relevant processor installed on the SAMA5D3x-MB motherboard. The eCos <vsn> and JLink_Vxxxx version names will change over time; you will need to use the path specific to the actual versions installed.

Other JLinkGDBServer options may be used as required, for example the -silent option reduces the output generated by the server.

A normal GDB debug session can then be started by connecting to the relevant JLinkGDBServer port (default 2331), for example:

(gdb) target remote localhost:2331
(gdb) load

A simpler sama5d3xek.jlink script is provided that does NOT initialise the clocks or DDR2-SDRAM, and can be used if explictly debugging ROM or SRAM startup types where execution of the relevant run-time initialization is desired.

From the GDB command-line when connected to JLinkGDBServer the “monitor regs” command can be used to see all of the non-VFP register state.

Note

Currently, as-of JLinkGDBServer version V484, there is no support for accessing the Cortex-A5 VFPv4-D16 (VFP) registers when using JLinkGDBServer. e.g. from the GDB “info all-reg” or “info float” commands. If low-level debugging of floating point operations is required then n alternative debugger should be used. The PEEDI hardware JTAG debugger provides support for displaying the VFP register state, as does the GDB stubs present in the software based RedBoot monitor.

PEEDI

For the Ronetix PEEDI, the sama5d31ek.peedi.cfg file should be used to setup and configure the hardware to an appropriate state to load programs. This includes setting up the PLLs and SDRAM controller. You can also check the Ronetix website http://download.ronetix.info/peedi/cfg_examples/cortex-a for updated versions.

	Note
	Use of a PEEDI debugger requires hardware modification of the standard SAMA5D3x-MB board, which will provide a 20-pin ARM JTAG connector at J9. The required modifications are detailed in the board's user manual.

The sama5d31ek.peedi.cfg file also contains an option to define whether hardware or software breakpoints are used by default, using the CORE0_BREAKMODE directive in the [PLATFORM_CortexA8] section (NOTE: The PEEDI firmware identifies not just A8 CPUs with the CortexA8 tag). Edit this file if you wish to use hardware break points, and remember to restart the PEEDI to make the changes take effect.

On the PEEDI, debugging can be performed either via the telnet interface or using arm-eabi-gdb and the GDB interface. In the case of the latter, arm-eabi-gdb needs to connect to TCP port 2000 on the PEEDI's IP address. For example:

(gdb) target remote 111.222.333.444:2000

By default when the PEEDI is powered up, the target will always run the initialization section of the sama5d31ek.peedi.cfg file, and halts the target. This behaviour is repeated with the PEEDI reset command.

If the board is reset (either with the 'reset', or by pressing the reset button) and the 'go' command is then given, then the board will boot as normal. Depending on how the platform jumper state is configured this could run either a second-level bootstrap, or a ROM RedBoot resident in flash.

By default the arm-eabi-gdb connection to the PEEDI will default to displaying the obsolete FPA registers. To enable access to the VFP registers a suitable target description file should be configured prior to connecting to the target system. This can either be done manually every time a GDB session is started, or more sensibly embedded in the users .gdbinit used to configure GDB.

The sama5d3x-tdesc.xml file can be used to define the target description using the GDB set tdesc filename <file> command. For example the .gdbinit could contain something similar to:

set tdesc filename $ECOS_REPOSITORY/packages/hal/arm/cortexa/sama5d3/sama5d3x_mb/current/misc/sama5d3x-tdesc.xml

So that it has the relevent target description available prior to the remote debug connection being established. This will allow access to the VFP registers via the PEEDI, for example via the GDB info all-reg command.

Consult the PEEDI documentation for information on other features.