MCU : STM32L496
JFlash version: v6.32i
We are facing the "Connection to target under reset failed" issue, when we try to program the board with STM32 MCU.
We were programming the board before with no issues. This error started appearing suddenly and now we are not able to program the board. When we scoped the reset pin of the MCU, the reset pin is going low when we click the connect button in the JFlash and clearly the board is resetting (We can see the firmware functionality restarting).
We tried the following:
Tied the BOOT0 pin to VDD and tried booting to the system memory and then tried programming. But this doesn't made any difference.
Tried always pulling down the reset pin to GND while trying to flash. We have ensured that there are no issues with the track leading to the JTAG interface of the MCU.
Could you please help to resolve this situation?
Is there any possibility that the firmware currently running in the MCU could prevent the flashing and lock the device?
STM32L4 has a feature called Read-out Protection (RDP). See section 1.1 of AN4758. If your firmware application sets (intentionally or accidentally) the RDP level to 1 or 2 in the "option bytes" memory area then the SWD/JTAG port is disabled from accessing flash memory (read, write, and erase).
If the RDP is level 0 or 1 then you should be able to read the option byte memory area. If RDP is level 1 then you should be able to set it back to level 0. The flash memory will be erased when setting RDP back to level 0 but the SWD/JTAG port will get re-enabled. If the RDP level is 2 then I believe there is no way to reset it.