USB : rename the data flow function name

debug/usb/README.md

@@ -157,6 +157,8 @@ Slave端(开发板),进入下载模式后枚举成MassStroage设备,循环等待
 写流程(usb_write)
 - Host发送cbw,其中cdb里包含写命令,并发送要写的数据,Slave返回csw
 
+下图中的所有术语是按主机的角度说明的
+
 ![work flow](./sequenceDiagram.png)
 
 Libusb编程核心步骤

debug/usb/sequenceDiagram.txt

@@ -5,12 +5,12 @@ participant "Slave(rockusb)" as slave
 
 host -> slave : send_cbw
 note right : usb_read
-slave -> host : send_data
-slave -> host : send_csw
+slave -> host : recv_data
+slave -> host : recv_csw
 
 host -> slave : send_cbw
 note right : usb_write
 host -> slave : send_data
-slave -> host : send_csw
+slave -> host : recv_csw
 
 @enduml