The version of xcode that supports Iphone OS 3.1.2(7D11)?

HELLO, I am working on XCODE 3.1.4 , my iphone have 3.1.2 os...But as this versi开发者_如何学编程on of xcode supports iphone os3.1.1 and below.. so plz help me as either tell me the newer version of xcode that supports iphone os 3.1.2 or should i downgrade my iphone os to 3.1.1,,

any assistance is really appreciated..

Ideally, you should be using the latest version of Xcode, which is included with the iPhone SDK. You can download the SDK from the iPhone Developer Center.