Hi @christian,
I am guessing the above mechanism is working as you have received the latest cores with the latest bootloader or did you patched the bootloader after you got the core? patching would be necessary, else the IWDG enabled in bootloader will always reset the core when put in low power mode(necessary for older cores).
Here is the Bootloader-patch firmware which will easily enable anyone in field to update to the latest bootloader without using JTAG programmer. Here is the core-firmware branch for this:
However care should be taken not to disturb the patch update process by accidentally removing usb power or through reset.
Following is the procedure to update the bootloader-patch
1)cd core-firmware
2)git pull
3)git checkout bootloader-patch-update
4)cd build [No need to run make]
5)Enter usb dfu/bootloader mode => Yellow flashes
6) dfu-util -d 1d50:607f -a 0 -s 0x08005000:leave -D core-firmware.bin
7)Upon execution, the bootloader should be updated within a second or two and normal core-firmware should start executing.
8)Congrats! your core is loaded with latest bootloader without the hassle of going through ST-Link JTAG programming
Now simply writing BKP->DR9 with 0xAFFF in your custom firmware should cause the bootloader to skip the enabling of IWDG after reset.