from chengdu to jiuzhaigou, stop at songpan

Three of us is going to visit jiuzhaigou from chengdu this December by bus. We plan to stay one night at Songpan because the bus journey from Chengdu to Jiuzhaigou is too long(10 hours) for us. Where should we get the bus at Chengdu? How long is the travelling time? Where do the bus stop at Songpan? Some say Chadianzi, some say Xinnanmen, confused..