I made simple stupid blinker on PA0 for ch32v203. It works fine. My issue that when it assembled with clang instead of GCC it creates bit different elf file which somehow magically erase/disable internal 28k USB bootloader code. "wchisp.exe flash main.elf" After programming this elf file i am not able anymore to use USB ISP, but SDI way still works. now wch-link over SDI shows empty region of 28k bootloader @0x1FFF8000. wchisp is flashing stack region over address 0x20002000 Isuue actually seems confirmed. https://github.com/ch32-rs/wchisp/issues/28 Any ideas to recover USB bootloader functionality?