HDSP_CHANBUF_SIZE
bzero(buf + offset * HDSP_CHANBUF_SAMPLES, HDSP_CHANBUF_SIZE);
ch->size = HDSP_CHANBUF_SIZE * hdsp_port_slot_count_max(ch->ports);
#define HDSP_DMASEGSIZE (HDSP_CHANBUF_SIZE * HDSP_MAX_SLOTS)