stm32f4-discovery st-link no target connected问题

Recently, when I was using the stm32f4-discovery board, I accidentally encountered the problem of st-link no target connected. It was working normally before, but suddenly this problem popped up. I thought it was a problem with the board. Later, after looking up information online, I found that it was not a problem with the board. The solution is as follows: (The development environment is MDK 4.6)

It shows "NO target connected" but the driver is fine. In the device manager, it shows that there is stlink because the two ports 14 and 13 of GPIOA are configured.  

”

The value of GPIOA_MODER after reset is: 0x2800 0000, that is, GPIO13\14 is configured as multiplexing mode. However, why does the SWD simulation and downloading fail when GPIO13\14 is configured as output in the program and the target chip is reset?

”

Solution:

1. First make sure the target board is powered on.

2. First, press and hold the reset button on the target board, then click Settings, and then release the reset button on the target board.

3. At this time, KEIL opens the Settings dialog box. Please confirm that there is SWD content before proceeding to the next step.

4. Power off the STM32F41Discovery board and then power it back on.

5. First, long press the reset button of STM32F4Discovery, then click the simulation or download button, and then release the reset button.

 Note: Clicking the simulation button and releasing the reset button here may not be successful every time. The time from clicking the simulation button to releasing the reset button is different each time. At a certain point, you can enter the simulation or download the program. The board will return to normal. But it should be noted that you must avoid the configuration of GPIO13\GPIO14 in the program.

Note: The time it takes to release the reset button cannot be too short or too long. It may take several attempts to succeed.