cocos2d application compatability with iphone4 and iPad

Dear all, I developed an application on cocos2d, it runs perfectly on simulator (iphone simulator 4) and on iphone 3, but on iphone 4 (device) only part of the application or view appears in the middle of the device all around it is a black area. How can i make my application compatable with iphone 开发者_如何学运维4? and does this make it automatically compatible with iPad or i should make other steps?

Regards

two steps to make an iphone app compatible with iphone4:

1. each image file should have its high-definition copy, which is twice bigger and suffixed with "-hd", say, add a hello-hd.png (100x100) for hello.png (50x50).

2. at the beginning, add one code line: [[CCDirector sharedDirector] enableRetinaDisplay:YES];

And it's all done. So far I cannot find a good way for iPad.

I just ported my App to iPad and used this snipped to load the right attributes

    NSString* imagePath;
    CGPoint imagePos;
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        // load iPad images and positions
        imagePath = @"image-ipad.png";
        imagePos = ccp(200,200);
    } else {
        // load iPhone images and positions
        imagePath = @"image.png";
        imagePos = ccp(100,100);
    }

Than set the path and position variable where you load the image