Why my ccid cannot send the message which the length is equal to package length

[DaHuFa]

Hello, everybody~
lately, I implement the CCID protocol. Then I test it. The first problem appeared. If the length of message is package length, the communication would become silent. Other circumstances, the communication is ok. You could help me?

[DaHuFa]

I got the answer from <Device Class: Smart Card>.

The CCID is required to send a Zero Length Packet (ZLP) following any Bulk-In
message that is a multiple of MaxPacketSize. This ZLP allows the CCID device driver to
be more efficient, and is generally considered “good-practice” for USB bulk-in pipes.

So, I should send a empty packet.