关于USBN9603中SETUP后更0字节包的问题

大家好！USBN9603在枚举过程中收到0字节的包，按照对RXS0的说明：This is the Receive Status register for the bidirectional Control Endpoint 0. To receive a SETUP packet after receiving a zero length OUT/SETUP packet, there are two copies of this register in hardware. One holds the receive status of a zero length packet, and another holds the status of the next SETUP packet with data. If a zero length packet is followed by a SETUP packet, the first read of this register indicates the status of the zero length packet (with RX_LAST set to 1 and RCOUNT set to 0) and the second read indicates the status of the SETUP packet.我收到如此字节后，应该再能读出下一个SETUP信息，但每次发生这种情况，第二次读出的RXS0均为0，为什么，需要如何读取？这个问题困扰我很久了，请赐教！！