[alsa-devel] Staying synced after underrun

I'm writing 48KHz stereo to Intel HD audio on my mobo, and I'd like to send it in parallel to both the analog and S/PDIF outputs, which share a clock source. If I open both devices, configure them with the same buffer space, and write the same data with snd_pcm_writei, how should I handle an underrun? Call snd_pcm_prepare on both device handles? If so, and the first device underruns, should I bother writing the buffer to the second device?