Problem with external oscillator : not able to flash anymore

[MMyar.1]

Hello all,

   I made my first "from scratch" STM32 board (in the past I always used demo boards).
  I cabled JTAG connector  : I was able to flash and debug from CubeIDE in SWD mode with a Stlinkv2, but did not succeed in JTAG mode, don't know why but it is not my today's topic. Works ok for what I did at the time.  I used the internal clock (HSI RC) and my application worked well.
   Then I wanted to add USB, so I had to use an HSE clock (it seems the HSI RC is not stable enougth). i added external quartz (ABLS 8 MHz with two 33pf capacitors), changed the clocking configuration from the Cube assistant, regenerated the code, then flashed. Now the chip is nor more accessible, it does not boot, and I can't flash it, even if I change the clocking setup to HSI RC again.
   I have two questions :
    - is there a way to get my board STM32F303 flashed again or is it dead ?
    - Is there a way to make some electrical diagnostics ?

  Here follows how I cabled the quartz.
   Best regards,
     Mikhaël

[jgnoss]

I don't think the crystal is your problem,

1. If HSE doesn't start it falls back to HSI,

2. Memory programming clock is always HSI.

I guess there's something else wrong in your code.

Try to hold NRST down and release it if the programmer starts to connect.

[jgnoss]

BTW, what's that Voltage divider on Boot0?

Pulling it down by a small R and decoupling it with 10n to GND should be the way to go