USHER & EX-WIFE IN COURT Child Custody Showdown

Usher and his ex-wife Tameka Raymond have gotten an ultimatum in their custodywar -- 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.

As we've reported, Usher and Tameka have been fighting over their kids for years -- Tameka wants full custody, claiming he secretly uses drugs. Usher has denied the allegations, asking for an increase in daddy time. The couple currently shares custody.