1. IPC Gateway对外提供的功能：
IPC的register/request/reply/notification服务。
2. IPC Gatew的实现原理：
各个具体的服务注册自己的回调函数，注册时提供服务自身的IPC Channel号。IPC Gateway 创建一个Map结构区记录各自的回调函数，当IPC Gateway接收到来字IPC layer的数据/消息,就会触发之前所注册的回调函数去处理数据。
Callback 函数的类型：
typedef void (*invoke_callback)(const void *ctx, UInt16 function, UInt8 *rx_data,Int32 len);
typedef void (*notification_callback)(UInt16 function, UInt8 *rx_data, Int32 len);
typedef void (*request_callback)(const void *ctx, UInt8 *rx_data, Int32 len);
3. 核心接口的设计：
/*Initialize the ipc gateway. Used to initialize the inside map. */
void ipc_gw_init();
/* Register callback function via channel number.*/
error_type ipc_gw_register(Int32 channel, notification_callback ntf_cb, request_callback req_cb);
/* Send request ipc message.*/
error_type ipc_gw_send_request(Int32 channel, UInt16 function,const UInt8 *data,Int32 len,const void *context, invoke_callback cb);
/*Send request ipc message without reply. */
error_type ipc_gw_send_request_no_reply(Int32 channel, UInt16 function,const UInt8 *data,Int32 len);
/* Reply the request after processing. */
error_type ipc_gw_send_reply(request_context_t *context, const UInt8 *data,Int32 len);
/* Send notification without reply. */
error_type ipc_gw_send_notification(Int32 channel, UInt16 function,const UInt8 *data,Int32 len);
/*Receive IPC message. Dispatch the message to respect registerd callback functions. */
error_type ipc_gw_receive_msg (Int32 channel, const UInt8* buf, Int32 len);