Always place graphics commands within the firstPage/nextPage loop.
u8g_Begin is not required.
void introScreen() {
u8g.firstPage();
do {
//u8g.drawBitmapP( 0, 0, 1, 8, rook_bitmap); //show image
u8g.drawRFrame(5, 10, 40, 30, 10);
u8g.setFont(u8g_font_unifont);
u8g.drawStr( 0, 20, "AAAAAAAAA");
} while( u8g.nextPage() )
delay(5000);
}
Oliver