SDPCM_SWHDR_LEN
#define SDPCM_HDRLEN (SDPCM_HWHDR_LEN + SDPCM_SWHDR_LEN)
hdr = pkt_next->data + bus->tx_hdrlen - SDPCM_SWHDR_LEN;
bus->tx_hdrlen = SDPCM_HWHDR_LEN + SDPCM_SWHDR_LEN;
bus->tx_hdrlen = SDPCM_HWHDR_LEN + SDPCM_SWHDR_LEN;