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** [tickets:#170] Using OpenOCD without the NRST signal**

**Status:** new
**Milestone:** 0.9.0
**Labels:** OpenOCD ST-LINK NRST signal 
**Created:** Fri Dec 01, 2017 12:56 PM UTC by Flavio Renga
**Last Updated:** Fri Dec 01, 2017 12:56 PM UTC
**Owner:** OpenOCD-Gerrit


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

Flavio



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