saasync
status = xpt_register_async(AC_FOUND_DEVICE, saasync, NULL, NULL);
xpt_register_async(0, saasync, periph, periph->path);
saasync, AC_FOUND_DEVICE, cgd);
xpt_register_async(AC_LOST_DEVICE, saasync, periph, periph->path);
static void saasync(void *callback_arg, uint32_t code,