Resolved! Is sprintf() supposed to support uint64_t numbers?
This compiles with no warnings or errors: char buf[256];uint64_t bignum = 0x123456789;sprintf(buf,"bignum: 0x%016llx, %llu\r\n",bignum,bignum);HAL_UART_Transmit_DMA(&huart1,(uint8_t *)buf, strlen(buf));This comes out the terminal:bignum: 0x0000000000...