Overview

Typically, since the STM32L476-DISCO motherboard has a built-in ST-LINK/V2-1 interface providing hardware debug support, eCos applications are loaded and run via the debugger arm-eabi-gdb or via the Eclipse IDE. The debugger then communicates with the “GDB server” provided by the relevant host ST-LINK/V2-1 support tool being used (e.g. OpenOCD).

Normally for release applications the ROM startup type would be used, with the application programmed into the on-chip flash for execution when the board boots. It is still possible to use the hardware debugging support to debug such flash-based ROM applications, and this may be the desired approach if the application is too large for execution from on-chip SRAM, or where all of the SRAM is required for application run-time use.

If off-chip Non-Volatile Memory (NVM) is used to hold the main application then the board can boot from the internal flash using a suitable boot loader. For example, the eCosPro BootUp ROM loader, where the BootUp code can start the main application (after an optional update sequence).

If required, it is still possible to program a GDB stub or RedBoot ROM image into on-chip Flash and download and debug via a serial connection (using USART3 on J8). In that case, eCos applications are configured for RAM startup and then downloaded and run on the board via the debugger arm-eabi-gdb, or via the Eclipse IDE as appropriate. However, the space available to applications with this approach is so limited as to make it essentially impractical.

Preparing ST-LINK/V2-1 interface

Use of the ST-LINK with STM32L4 microcontrollers and OpenOCD currently requires that the ST-LINK/V2-1 firmware is version V2.J20.XXX and not a more recent version. The firmware for the ST-LINK/V2-1 interface can be checked, and updated if needed, using a tool available from STMicroelectronics. The firmware version is also reported when the openocd command is executed (using a suitable configuration file). For example, the following OpenOCD output reports JTAG v20:

Info : STLINK v2 JTAG v20 API v2 SWIM v11 VID 0x0483 PID 0x374B

Future revisions of ST-LINK firmware may restore compatibility, but would require testing to confirm this. The user should refer to the ST “ST-LINK/V2-1 firmware upgrade” (RN0093) Release Note, which provides details on upgrading the ST-Link firmware on Linux, Mac OS X and Windows hosts.

Programming ROM images

Since the STM32L476-DISCO board has a built-in ST-LINK/V2-1 SWD interface, the USB host connection (CN1) and suitable host software (e.g. The OpenOCD package openocd tool) can be used to program the flash.

The openocd GDB server can directly program flash based applications from the GDB load command.

	Note
	The openocd command being used should have been configured and built to support the ST-LINK/V2-1 interface. This is achieved by specifying the --enable-stlink when configuring the OpenOCD build. Additional information on running openocd may be found in the OpenOCD notes.

For example, assuming that openocd is running on the same host as GDB, and is connected to the target board the following will program the “bootup.elf” application into the on-chip flash:

$ arm-eabi-gdb install/bin/bootup.elf
GNU gdb (eCosCentric GNU tools 4.7.3j) 7.8.2
[ … GDB output elided … ]
(gdb) target remote localhost:3333
hal_reset_vsr () at path/hal_misc.c:171
(gdb) load
Loading section .rom_vectors, size 0x14 lma 0x8000000
Loading section .text, size 0x3adc lma 0x8000018
Loading section .rodata, size 0x6c0 lma 0x8003af8
Loading section .data, size 0x6dc lma 0x80041b8
Start address 0x8000018, load size 18572
Transfer rate: 14 KB/sec, 4643 bytes/write.
(gdb)

Alternatively, the openocd telnet interface can be used to manually program the flash. By default the openocd session provides a comand-line via port 4444. Consult the OpenOCD documentation for more details if a non-default openocd configuration is being used.

With a telnet connection established to the openocd any binary data can easily be written to the on-chip flash. e.g.

$ telnet localhost 4444
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Open On-Chip Debugger
> flash write_image test.bin 0x08000000
wrote 32518 bytes from file test.bin in 1.073942s (29.569 KiB/s)

To create a binary for flash programming the arm-eabi-objcopy command is used. This converts the, ELF format, linked application into a raw binary. For example:

$ arm-eabi-objcopy -O binary programname programname.bin