cas_ringsize
v = cas_ringsize(CAS_NTXDESC /*XXX*/) << 10;
v = cas_ringsize(CAS_NRXDESC) << CAS_RX_CONFIG_RXDRNG_SZ_SHIFT;
v |= cas_ringsize(32) << CAS_RX_CONFIG_RXDRNG2_SZ_SHIFT;
int cas_ringsize(int);