APC_CNVA
nextaddr = APC_READ(sc, APC_CNVA) +
APC_WRITE(sc, APC_CNVA, nextaddr);
APC_WRITE(sc, APC_CNVA, p->dmamap->dm_segs[0].ds_addr);
nextaddr = APC_READ(sc, APC_CNVA) + chan->cs_blksz;
APC_WRITE(sc, APC_CNVA, nextaddr);