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