Why is Pap upset with Huck? What social commentary is Twain making about older generation vs their children?

Pap is upset that Huck won't give him the money he had. He is also upset that Huck is living a "civilized" life while he is a drunken vagabond. I don't think this is a reflection of a generation gap more than Pap being a drunken abusive sod and Huck trying to get on with his life.