override fun onResume() {
    super.onResume()
    Observable.interval(initialDelay, 60, TimeUnit.SECONDS)
            .flatMap {
                trainBoardApi.liveEta() // retrofit
            }
            .compose(bindToLifecycle())
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe({ response ->
                lastLoadSuccessTimestamp = System.currentTimeMillis()
                // update UI here...
                adapter.notifyDataSetChanged()
            }, { e ->
                // show error message
            })
}