Usher & Ex-Wife in Court -- Child Custody Showdown

Usher and his ex-wife Tameka Raymond have gotten an ultimatum in their custody war -- they're at the Atlanta courthouse trying to settle it, and if they can't the judge is going to lay down the law.

The singer and his ex-wife showed up to Fulton County Court this morning -- where a judge ordered the couple to try and hash out a temporary custody agreement in private mediation.

They've had all morning to work something out -- but if they don't come to terms soon ... they'll face the judge again this afternoon ... when he'll impose a temporary order, deciding how Usher and Tameka will split their time with their kids.

The order will also address child support.