While designing Electronic speed controllers for a 6s battery, an stm32 was decided to use as the MCU.
After receiving our first PCBs, we were unable to successfully program them with the stlinkv3 minie. Attached is an image of the schematic of where the STM lies on the board as well as the attached components. When the boards first came in the stm32 was able to be flashed with a program, but after the first flash they could not be connected to any more. This is with using an external power supply as the stlink v3 didn't seem to provide power as the prg tool was unable to detect the chip.
After continued testing (and changing out the mcu) the issue persisted although with a slight deviation, it would allow us to program it once or twice but when we clear the flash, it would lose connection and throw an error of dev_target_held_under_reset. In case it is relevant, the only connection type that can even read the flash of the chip is hot plug but that is unable to change the data as far as I am aware.
Trying to alleviate this issue, the reset decoupling capacitor was removed in case there was something causing a short, as well as a blank pcb being used with just the microcontroller and capacitors included. Still no luck. In case it was the program that was being applied, the program was changed to a simple blink program, however, even this will not work. We have 2 different layout/schematics for two different tasks that both use the same microcontroller and neither of them are able to program. Either the program tool says no stm32 found, or it says that it is held under reset. I have searched many forums and have not found any solutions that work, including using a 10kOhm resistor from 3.3v to the reset pin in case the internal pullup was not providing enough power to the pin. None of these solutions work. The original software (bootloader and firmware of AM32) works on a nucleo test board with the same steps used to program the custom pcb and the same microcontroller (although different package, they are both 128k flash g071).
This is very frustrating as we have not been able to even test the hardware that we have designed for the past 2 months as we have been stuck trying to program the boards for so long. Any help or solutions that could be provided would be absolutely lovely. The layout of the microcontroller for one of the PCBs is also provided with the reset path highlighted. (Continuity of all of the paths has already been tested and there are no issues in that respect.
