Keep One's Pecker Up Meaning

(chiefly Britain, idiomatic) To remain cheerful; keep smiling.

Example: 1880, Talbot Baines Reed, The Fifth Form at Saint Dominic's,
  â€œOf course you will,” said Wraysford, cheerily; “it’s hard lines at first. Keep your pecker up, young ’un.” The young ’un, despite this friendly advice, felt very far from keeping up his pecker. But he did his best, and worked his face into a melancholy sort of a smile.
1922, James Joyce, Ulysses, Episode 12, The Cyclops
  --Keep your pecker up, says Joe. She'd have won the money only for the other dog.
1977 W. Somerset Maugham, Collected short stories,
  "Nerves a bit dicky, eh? Playing a tune to keep your pecker up?"
2003 Janet Floyd, Laurel Forster, The recipe reader: narratives, contexts, traditions‎,
  All you need is a box of goodies to keep your pecker up, ...