I picked up this book by Janie Clayton, it's pretty good: <a href="https://www.amazon.co.uk/Metal-Programming-Guide-Tutorial-Reference/dp/0134668944/ref=sr_1_1?ie=UTF8&qid=1530452201&sr=8-1&keywords=programming+metal" rel="nofollow">https://www.amazon.co.uk/Metal-Programming-Guide-Tutorial-Re...</a>