IXGBE_RXPBSIZE
rxpb = IXGBE_READ_REG(hw, IXGBE_RXPBSIZE(0)) >> 10;
fcrth = IXGBE_READ_REG(hw, IXGBE_RXPBSIZE(i)) - 0x6000;
IXGBE_WRITE_REG(hw, IXGBE_RXPBSIZE(0), 384 << IXGBE_RXPBSIZE_SHIFT);
rx_pb_size = IXGBE_READ_REG(hw, IXGBE_RXPBSIZE(tc));