Using OpenOCD without the NRST signal connected to the board

Open source ARM Debugger

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Using OpenOCD without the NRST signal connected to the board

Post by Errand » Thu Nov 30, 2017 2:49 pm

Hi everyone,
i'm are working on the development of a new prototype using the NUCLEO F303RE platform.
I need to power it by using an external 3.3V power supply, but I still want to program and debug it by using the integrated ST-LINK.
If using an external 3V3 power supply, the datasheet indicates that the following jumpers must be removed:
- SB2 (3V3 regulator)
- SB12 (NRST)
The problem is that if I remove SB12, I can't use the integrated ST-LINK (the NRST signal is unconnected!).

This is the question:
What are the correct parameters for the OpenOCD to flash and debug the NUCLEO F303RE platform without the NRST signal connected to the board?

For your complete information, I report hereafter the answer of the ST MCU Support Team:

"Dear customer,

STLINK does NOT require the NRST line to work properly. NRST is used ONLY for (obviously) hardware resetting the MCU and for connecting to a target with a software disabled SWD pins, or in a low power sleep mode.

This is an issue with your debugger PC software (typically OpenOCD may fail with incorrect settings, but there is not much STMicroelectronics can do about that). With STLink Utility, or any other toolchain (Keil MDK-ARM, IAR Workbench) that support the STLINK natively, they won't fail.

If your debugger software fails to work properly without NRST, then you may leave the NRST line also connected. (You may need it anyway, if you will work with low power modes).

Best regards,
ST MCU Support Team"

Thanks in advance


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