Patent Publication Number: US-11039389-B2

Title: Information processing apparatus, control method, information processing system, and non-transitory computer-readable storage medium with executable control program stored thereon

Description:
This nonprovisional application is based on Japanese Patent Application No. 2018-072322 filed with the Japan Patent Office on Apr. 4, 2018, the entire contents of which are hereby incorporated by reference. 
     FIELD 
     The present technology relates to an information processing apparatus capable of receiving a packet from another apparatus through radio communication, a control method performed in the information processing apparatus, an information processing system including the information processing apparatus, and a non-transitory computer-readable storage medium with an executable control program stored thereon, the control program being executed by the information processing apparatus. 
     BACKGROUND AND SUMMARY 
     A technology of exchanging data through radio communication between information processing apparatuses has been known. For example, a communication terminal including transmission and reception means for transmitting and receiving data between the terminal and another communication terminal within a prescribed positional range has been known. 
     When timing of exchange of data is not shared between apparatuses, data is transmitted at unexpected timing. Therefore, an information processing apparatus is continuously or periodically in a data reception awaiting state. 
     On the other hand, there is a need for reduction in power consumption. In particular, low power consumption is required in a portable information processing apparatus. 
     The present technology provides an approach for reducing power consumption in a configuration in which a packet is repeatedly received from another apparatus through radio communication. 
     An exemplary embodiment provides an information processing apparatus according to one embodiment, the information processing apparatus including a receiver configured to repeatedly receive a packet from another apparatus through radio communication, a memory configured to store the packet received by the receiver, an information processing unit configured to perform information processing and to make mode transition at least between a first mode and a second mode lower in power consumption than the first mode, a mode management module configured to have the information processing unit make mode transition from the second mode to the first mode when at least any one of the number of packets stored in the memory, a data amount of a packet stored in the memory, and a content of a packet stored in the memory satisfies a first condition, and a reading module configured to read the packet stored in the memory when the information processing unit makes mode transition from the second mode to the first mode. The information processing unit makes mode transition from the first mode to the second mode when the information processing unit has performed processing including reading of the packet by the reading module. 
     According to the embodiment, even when the information processing unit is in the second mode lower in power consumption, the receiver is able to receive a packet. When a data amount of the packet received by the receiver and stored in the memory satisfies the first condition, the information processing unit makes mode transition from the second mode to the first mode and performs necessary processing, and again makes mode transition to the second mode. By making use of such mode transition of the information processing unit, power consumption in the information processing apparatus can be reduced. 
     The first condition may include a condition that the number of received packets exceeds a prescribed number. By adopting such a configuration, mode transition between the first mode and the second mode can be made in accordance with the number of received packets. 
     The first condition may include a condition that a data amount of the received packet exceeds a prescribed data amount. By adopting such a configuration, mode transition between the first mode and the second mode can be made in accordance with the data amount of the received packet. 
     The first condition may include a condition that the received packet includes prescribed data. By adopting such a configuration, mode transition between the first mode and the second mode can be made in accordance with a content of the received packet. 
     The memory may store a packet which satisfies a second condition among packets received by the receiver. By adopting such a configuration, more types of packets can be stored while a storage area in the memory is efficiently used. 
     The second condition may include a condition that the packet received by the receiver conforms to a prescribed format. By adopting such a configuration, only a necessary packet can be selected by more simplified processing from among a variety of packets received by the receiver. 
     The second condition may at least partly be determined based on identification information of a packet received in advance by the receiver. By adopting such a configuration, even when identical packets are received in a redundant manner, redundant storage of such identical packets in the memory can be prevented. 
     The identification information may be at least one of a value representing data constituting the packet received by the receiver and at least a part of data constituting the packet received by the receiver. By adopting such a configuration, a packet identical to the packet received by the receiver can reliably be specified. 
     The value representing the data constituting the packet received by the receiver may be a hash value calculated from the data constituting the packet. By adopting such a configuration, processing for determining whether or not packets are identical to each other can be simplified. 
     The hash value may be added by a sender of a packet of interest. By adopting such a configuration, a reception side can perform processing in connection with identity of packets faster and can also check authenticity of the received packet itself. 
     The second condition may at least partly be determined based on a packet which is stored in the memory but has not yet been read into the information processing unit. By adopting such a configuration, redundant storage of identical packets received at temporally proximate timing can be prevented. 
     The second condition may at least partly be determined by the information processing unit. By adopting such a configuration, a packet to be stored can be determined with a result of information processing performed by the information processing unit being reflected. 
     In the second mode, reception by the receiver and storage in the memory may repeatedly be performed. By adopting such a configuration, packets can successively be received. 
     The reading module may erase, after the reading module reads the packet stored in the memory, that packet from the memory. By adopting such a configuration, packets can successively be received with a storage capacity being limited. 
     The receiver may receive the packet without establishing connection to another apparatus. By adopting such a configuration, processing involved with data transmission can be simplified, and consequently a time period required for transmission and reception of a packet can be shortened. 
     Handshaking with another apparatus does not have to be performed. By adopting such a configuration, a time period required for transmission and reception of a packet can further be shortened. 
     The receiver may provide time information to the received packet. By adopting such a configuration, even though the information processing unit processes a received packet at a later time, timing of actual reception of each packet to be processed can be known and information processing requiring reception timing can also be performed. 
     The packet may include data on a game application. By adopting such a configuration, the information processing apparatus according to the present embodiment can also be applied to a game application. 
     A radio processing unit which includes at least the receiver and is separated from the information processing unit may be arranged in the information processing apparatus, and the information processing unit may be higher in power consumption than the radio processing unit. By adopting such a configuration, such a form of use that a radio processing unit relatively lower in power consumption is responsible for reception of a packet and an information processing unit relatively higher in power consumption collectively processes received packets only for a required period is allowed. 
     The information processing unit may be configured to sense a signal from the radio processing unit indicating mode transition also in the second mode. By adopting such a configuration, the information processing unit can make mode transition from the second mode to the first mode at any timing when a signal indicating mode transition is given from the radio processing unit. 
     The information processing apparatus may further include a transmitter configured to transmit a packet to another apparatus. As the transmitter of the information processing apparatus transmits a packet to another apparatus, data can bidirectionally be exchanged between information processing apparatuses. 
     The mode management module may have the information processing unit make mode transition from the second mode to the first mode without depending on a data amount of the packet stored in the memory, in response to the packet received by the receiver including instructions to make mode transition to the second mode. By adopting such a configuration, a request for having the information processing unit perform some kind of processing at any timing can be met. 
     According to another embodiment, a control method in an information processing apparatus is provided, the information processing apparatus including a receiver configured to repeatedly receive a packet from another apparatus through radio communication, a memory configured to store the packet received by the receiver, and an information processing unit configured to perform information processing and to make mode transition at least between a first mode and a second mode lower in power consumption than the first mode. The control method includes having the information processing unit make mode transition from the second mode to the first mode when at least any one of the number of packets stored in the memory, a data amount of a packet stored in the memory, and a content of a packet stored in the memory satisfies a first condition, performing processing including reading of the packet stored in the memory when transition from the second mode to the first mode is made, and the information processing unit making mode transition from the first mode to the second mode after the information processing unit has performed the processing. 
     According to yet another embodiment, an information processing system including a first information processing apparatus and a second information processing apparatus is provided. The first information processing apparatus includes a receiver configured to repeatedly receive a packet from the second information processing apparatus through radio communication, a memory configured to store the packet received by the receiver, an information processing unit configured to perform information processing and to make mode transition at least between a first mode and a second mode lower in power consumption than the first mode, a mode management module configured to have the information processing unit make mode transition from the second mode to the first mode when at least any one of the number of packets stored in the memory, a data amount of a packet stored in the memory, and a content of a packet stored in the memory satisfies a first condition, and a reading module configured to read the packet stored in the memory when the information processing unit makes mode transition from the second mode to the first mode. The information processing unit makes mode transition from the first mode to the second mode when the information processing unit has performed processing including reading of the packet by the reading module. 
     According to still another embodiment, a non-transitory computer-readable storage medium with an executable control program stored thereon is provided, the control program being executed by an information processing apparatus. The information processing apparatus includes a radio communication unit including a receiver configured to repeatedly receive a packet from another apparatus through radio communication, a memory configured to store the packet received by the receiver, and an information processing unit configured to perform information processing and to make mode transition at least between a first mode and a second mode lower in power consumption than the first mode. The control program, when executed by the information processing apparatus, causes the radio communication unit to perform having the information processing unit make mode transition from the second mode to the first mode when at least any one of the number of packets stored in the memory, a data amount of a packet stored in the memory, and a content of a packet stored in the memory satisfies a first condition. The information processing unit performs processing including reading of the packet stored in the memory when the information processing unit makes transition from the second mode to the first mode, and makes mode transition from the first mode to the second mode after the information processing unit has performed the processing. 
     The foregoing and other objects, features, aspects and advantages of the exemplary embodiments will become more apparent from the following detailed description of the exemplary embodiments when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary illustrative non-limiting drawing illustrating an information processing system according to the present embodiment. 
         FIG. 2  shows an exemplary illustrative non-limiting drawing illustrating a hardware configuration of an information processing apparatus according to the present embodiment. 
         FIG. 3  shows an exemplary illustrative non-limiting drawing illustrating a procedure for transmitting and receiving a packet in the information processing apparatus according to the embodiment. 
         FIG. 4  shows an exemplary illustrative non-limiting drawing illustrating a procedure for exchanging data in the information processing system according to the present embodiment. 
         FIG. 5  shows an exemplary illustrative non-limiting drawing illustrating a functional configuration for managing an operation mode in the information processing apparatus according to the present embodiment. 
         FIG. 6  shows an exemplary illustrative non-limiting time chart illustrating management of the operation mode in the information processing apparatus according to the present embodiment. 
         FIG. 7  shows an exemplary illustrative non-limiting drawing illustrating a data format of a packet transmitted by the information processing apparatus according to the present embodiment. 
         FIG. 8  shows an exemplary illustrative non-limiting drawing illustrating processing for filtering a reception packet in the information processing apparatus according to the present embodiment. 
         FIG. 9  shows an exemplary illustrative non-limiting drawing illustrating a configuration for performing processing for filtering a reception packet in the information processing apparatus according to the present embodiment. 
         FIG. 10  shows an exemplary illustrative non-limiting flowchart illustrating a processing procedure involved with transmission and reception of a packet in the information processing apparatus according to the present embodiment. 
         FIG. 11  shows an exemplary illustrative non-limiting drawing illustrating a data structure of a reception packet stored in a memory of the information processing apparatus according to the present embodiment. 
     
    
    
     DETAILED DESCRIPTION OF NON-LIMITING EXAMPLE EMBODIMENTS 
     The present embodiment will be described in detail with reference to the drawings. The same or corresponding elements in the drawings have the same reference characters allotted and description thereof will not be repeated. 
     [A. Information Processing System] 
     Overview of an information processing system  1  according to the present embodiment will initially be described with reference to  FIG. 1 . 
     Information processing system  1  includes a plurality of information processing apparatuses  100 - 1 ,  100 - 2 ,  100 - 3 , . . . (which are also collectively referred to as an “information processing apparatus  100 ” below) capable of exchanging data through radio communication. 
     Each of information processing apparatuses  100 - 1 ,  100 - 2 ,  100 - 3 , . . . transmits a packet  300  containing information held by each apparatus periodically or for each arbitrary event. Each information processing apparatus  100  receives one packet  300  or a plurality of packets  300 . 
     Packet  300  is typically transmitted as being broadcast. A scheme of transmission of packet  300  is not limited to broadcasting, but may be multicasting, or unicasting when destination information processing apparatus  100  can be specified by any method. 
     Each of information processing apparatuses  100 - 1 ,  100 - 2 ,  100 - 3 , . . . also enters a reception awaiting state for receiving packet  300 . When packet  300  from any information processing apparatus  100  arrives during a period of this reception awaiting state (which is also referred to as a “reception awaiting period” below), packet  300  is received. 
     Information processing system  1  as shown in  FIG. 1  is applicable to such an application as allowing exchange of any information among an unspecified number of users. A game application is assumed as one example of such an application. In this case, a packet transmitted or received by each information processing apparatus  100  includes data on a game application. 
     In another example, for example, the information processing system can be applied also to such an application as allowing distribution of any coupon. In this case, a packet transmitted and received by each information processing apparatus  100  contains data on a coupon. 
     The term “packet” herein encompasses any packet transmitted by each information processing apparatus  100  and may encompass packets in other data formats in addition to a packet in a data format as will be described later. 
     Examples of radio communication employed by information processing apparatus  100  include wireless local area network (LAN) in conformity with IEEE802.11 standards and Bluetooth®. As will be described later, in information processing system  1  according to the present embodiment, no such procedure as handshaking is not performed in exchange of packet  300  among information processing apparatuses  100 . 
     Though information processing system  1  according to the present embodiment is applicable to any application, it can be implemented as a game system by way of typical example. In such an implementation, information processing apparatus  100  can also be called a game apparatus. Information processing apparatus  100  can be implemented by a portable device such as a smartphone or a tablet without being limited to the game apparatus. 
     Not only information processing apparatus  100  implementing information processing system  1  shown in  FIG. 1  may be determined in advance but also the information processing system may autonomously be implemented by presence of information processing apparatuses  100  with a function to transmit and receive a packet within an area where they can communicate with one another. The technical scope of the present disclosure may encompass also information processing system  1  autonomously implemented by any information processing apparatuses  100 . 
     [B. Information Processing Apparatus] 
     Overview of information processing apparatus  100  implementing information processing system  1  according to the present embodiment will now be described with reference to  FIG. 2 . 
     Information processing apparatus  100  includes a main control unit  110 , a radio communication unit  120 , an operation unit  102 , an indicator  104 , a display  106 , a speaker  108 , and a battery  140 . 
     Main control unit  110  is an entity which controls overall processing in information processing apparatus  100  and also referred to as an application processor. Main control unit  110  includes a processor  112 , a main memory  114 , and a non-volatile memory  116  as main components. 
     Processor  112  is implemented by a central processing unit (CPU) or a graphical processing unit (GPU) and executes a program stored in non-volatile memory  116  by developing the program on main memory  114 . Main memory  114  is implemented by a dynamic random access memory (DRAM) or a static random access memory (SRAM) and holds data in a volatile manner. Non-volatile memory  116  is implemented by a flash memory or an electrically erasable programmable read-only memory (EEPROM) and holds data in a non-volatile manner. Non-volatile memory  116  typically stores a control program  130  which provides a basic function of information processing apparatus  100 , an application program  132  for performing any game or information processing, and reception data  134  including a packet received by radio communication unit  120  (which is also referred to as a “reception packet” below). Reception data  134  includes a content in one reception packet or a plurality of reception packets and is referred to as appropriate by application program  132 . 
     Main control unit  110  may be mounted as a system large scale integration (LSI) including components described above. In this case, the main control unit may be mounted in a form of a system-on-a-chip (SoC) in which the components are integrated. 
     Radio communication unit  120  corresponding to a radio processing unit has a function to repeatedly receive a packet  300  from another apparatus through radio communication and transmit packet  300  to another apparatus. Radio communication unit  120  can take, as typical operation states, (1) a transmission state in which data is transmitted, (2) a reception state in which data is received, (3) a transmission and reception state in which data is transmitted and received, and (4) a power saving state in which neither of transmission and reception is performed. Radio communication unit  120  includes a radio module  122 , a radio controller  124 , and a buffer memory  128  as main components. 
     Radio module  122  is a circuit which transmits and receives a radio signal to and from another information processing apparatus  100  through an electrically connected antenna  123 , and includes a reception circuit  122 RX and a transmission circuit  122 TX. Reception circuit  122 RX corresponds to the receiver which repeatedly receives a packet from another apparatus through radio communication and transmission circuit  122 TX corresponds to a transmitter which transmits a packet to another apparatus. The receiver can include not only radio module  122  but also antenna  123 . 
     Radio module  122  basically transmits and receives a packet through any one channel among a plurality of channels prepared in advance. A channel used for transmission of a packet may be the same as or different from a channel used for reception of a packet. A plurality of channels may simultaneously be used as necessary. 
     More specifically, radio module  122  includes a high-frequency generation circuit, a modulation circuit, a demodulation circuit, an encoding circuit, and the like. A configuration for setting an appropriate frequency or an appropriate modulation scheme is adopted for radio module  122  in accordance with an implemented communication scheme. 
     Radio controller  124  controls transmission and reception of a radio signal by radio module  122  by execution by processor  126  of firmware  127  representing a control program. A circuit such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA) instead of processor  126  may perform the entire or partial processing performed by radio controller  124 . 
     Buffer memory  128  temporarily stores data (packet  300 ) to be sent from radio module  122  and data received by radio module  122  (reception packet). Buffer memory  128  is typically implemented by a first-in first-out (FIFO) memory and writing and reading of data into and from buffer memory  128  are controlled by radio controller  124  and main control unit  110 . 
     An example in which buffer memory  128  is mounted as a part of radio communication unit  120  is shown in the configuration shown in  FIG. 2 . Without being limited as such, a function corresponding to buffer memory  128  may be arranged in main control unit  110  or in a portion other than main control unit  110  and radio communication unit  120 . When a function corresponding to buffer memory  128  is mounted on main control unit  110 , a partial area in main memory  114  or non-volatile memory  116  may be used as a buffer memory. 
     Radio communication unit  120  as the radio processing unit thus includes radio module  122  corresponding to the receiver. Basically, main control unit  110  corresponding to the information processing unit is higher in power consumption (an amount of electric power (W) consumed per unit time) than radio communication unit  120 . 
     Operation unit  102  accepts an operation by a user and outputs information representing a content of the operation by the user to main control unit  110 . Typically, operation unit  102  includes a push button, a control lever, a touch panel, or a mouse. Alternatively, a controller which is separate from information processing apparatus  100  and connected through a wire or wirelessly may be included as operation unit  102 . 
     Indicator  104  is arranged as being exposed at a surface of information processing apparatus  100  and gives a visual notification to a user in response to a command from main control unit  110 . Typically, indicator  104  includes a light emitting diode (LED). 
     Display  106  is arranged on a main surface of information processing apparatus  100  and shows any image in response to a command from main control unit  110 . Display  106  is typically implemented by a liquid crystal display (LCD). 
     Speaker  108  is arranged as being partially exposed at the surface of information processing apparatus  100  and gives an audio notification to a user in response to a command from main control unit  110 . 
     Battery  140  supplies electric power to main control unit  110  and radio communication unit  120 . As will be described later, main control unit  110  can switch between an operation mode in which normal processing can be performed (which is also referred to as a “normal mode” below) and an operation mode lower in power consumption than the normal mode (which is also referred to as a “power saving mode” below). When main control unit  110  is set to the power saving mode, electric power lower than electric power supplied to main control unit  110  in the normal mode is supplied to main control unit  110 . 
     The “power saving mode” can be called, for example, a stand-by mode or a sleep mode. The present disclosure can be applied to any apparatus or any system including two operation modes different in power consumption from each other. 
     An example in which main control unit  110  as a whole makes mode transition to the power saving mode will be shown in the description below as a typical example. An example in which only a part of main control unit  110  (typically processor  112 ) makes transition to the operation mode lower in power consumption than the normal mode, however, can also be encompassed in the concept of the “power saving mode” in the present disclosure. 
     By receiving electric power from battery  140 , radio communication unit  120  maintains a state that it is able to transmit and receive a radio signal. Since switching between a transmission period and a reception period (or a reception awaiting period) is periodically made, a state that transmission or reception is enabled does not always continue. 
     [C. Procedure for Transmission and Reception of Packet] 
     In information processing system  1  according to the present embodiment, each information processing apparatus  100  periodically transmits (broadcasts) packet  300 . As another information processing apparatus  100  located proximate to information processing apparatus  100  which has transmitted packet  300  receives that transmitted packet  300 , transmission of packet  300  is successful. 
     Referring to  FIG. 3 , each information processing apparatus  100  transmits (broadcasts) packet  300  every predetermined transmission cycle T 1 . Packet  300  in each transmission cycle may be transmitted a plurality of times. Namely, identical packets  300  may be transmitted a plurality of times like a burst. 
     Each information processing apparatus  100  is in a stand-by (reception awaiting) state of awaiting packet  300  from another information processing apparatus  100  while it is not transmitting packet  300  (a reception awaiting period DT). Reception awaiting period DT may be provided for each reception cycle T 2 . 
     For example, transmission cycle T 1  may be set to 100 [msec.] and reception cycle T 2  may be set to several ten times as long as transmission cycle T 1  (for example, 3 [sec.]). 
     Intermittent transmission of packet  300  and wait for packet  300  can achieve reduction in power consumption in radio communication unit  120  of information processing apparatus  100 . 
     One example of a data exchange procedure in information processing system  1  according to the present embodiment will be described with reference to  FIG. 4 .  FIG. 4  shows an example in which information processing apparatus  100 - 1  and information processing apparatus  100 - 2  are located within an area where they can communicate with each other. 
     Information processing apparatus  100 - 1  transmits packet  300  at times t 1 , t 2 , t 3 , t 4 , . . . and receives packet  300  during a period until time t 3  after transmission of packet  300  at time t 2 . 
     Information processing apparatus  100 - 2  transmits packet  300  at times t 1 ′, t 2 ′, t 3 ′, . . . and receives packet  300  from another information processing apparatus  100  during a period until time t 2 ′ after transmission of packet  300  at time t 1 ′. 
     In the example shown in  FIG. 4 , information processing apparatus  100 - 2  is in a state of awaiting reception of packet  300  at time t 2  when information processing apparatus  100 - 1  transmits packet  300 . Therefore, information processing apparatus  100 - 2  receives packet  300  transmitted from information processing apparatus  100 - 1 . 
     Alternatively, information processing apparatus  100 - 1  is in a state of awaiting reception of packet  300  at time t 2 ′ when information processing apparatus  100 - 2  transmits packet  300 . Therefore, information processing apparatus  100 - 1  receives packet  300  transmitted from information processing apparatus  100 - 2 . 
     As shown in  FIG. 4 , each information processing apparatus  100  transmits and receives packet  300  at timing unique to each apparatus. Information processing apparatuses  100  are not exactly identical in transmission cycle and reception cycle. Therefore, when one information processing apparatus  100  is in the reception awaiting state at timing of transmission of packet  300  by another information processing apparatus  100 , transmission of packet  300  is successful. 
     As shown in  FIG. 4 , when each information processing apparatus  100  transmits a packet and any information processing apparatus  100  in the reception awaiting state receives that packet in information processing system  1 , the packet can successfully be transmitted. A receiver  1202  (radio module  122 ) of radio communication unit  120  which implements information processing apparatus  100  can thus receive a packet without establishing connection to another information processing apparatus  100 . By adopting such a protocol obviating the need for connection between information processing apparatuses  100 , simple and fast data exchange can be realized. Since timing of a next communication event does not have to be adjusted (when next communication will come from a destination is still unknown), a connection procedure can be simplified. 
     Under the protocol adopted in the present embodiment, receiver  1202  (radio module  122 ) of radio communication unit  120  implementing information processing apparatus  100  is configured not to transmit a response even though it receives a packet. 
     In information processing system  1  according to the present embodiment, handshaking between information processing apparatuses  100  is not required. Therefore, if only transmission and reception of packet  300  are well timed between information processing apparatuses  100 , packet  300  can immediately be transmitted. 
     [D. Management of Operation Mode] 
     Management of an operation mode in information processing apparatus  100  implementing information processing system  1  according to the present embodiment will now be described. 
     Information processing apparatus  100  according to the present embodiment includes main control unit  110  and radio communication unit  120  (see  FIG. 2 ). Main control unit  110  is higher in power consumption than radio communication unit  120 . Therefore, radio communication unit  120  is mainly responsible for processing for transmitting and receiving (waiting for reception of) packet  300  involved with data exchange. Though main control unit  110  performs information processing as necessary, it maintains the power saving mode while it does not have to perform information processing. By thus appropriately managing the operation mode of main control unit  110 , power consumption in information processing apparatus  100  as a whole can be reduced. 
     Referring to  FIG. 5 , main control unit  110  corresponds to the information processing unit, and it can perform information processing and can make mode transition at least between the normal mode (a first mode) and the power saving mode (a second mode) lower in power consumption than the normal mode. 
     Main control unit  110  includes a data reading module  1102  and a data processing module  1104  as its functional configuration. Data reading module  1102  and data processing module  1104  are typically implemented by execution by processor  112  of control program  130  and/or application program  132  (see  FIG. 2 ). 
     Radio communication unit  120  includes receiver  1202 , a memory  1204 , and a mode management module  1208  as its functional configuration. Typically, receiver  1202  is implemented by radio module  122 , memory  1204  is implemented by buffer memory  128 , and mode management module  1208  is implemented by execution of firmware  127  by radio controller  124 . 
     Receiver  1202  repeatedly receives packet  300  from another information processing apparatus  100  through radio communication. Memory  1204  cumulatively stores reception packet  1206  received by receiver  1202 . Memory  1204  accumulates reception packet  1206  up to a predetermined upper limit number of packets. When the number of reception packets  1206  accumulated in memory  1204  reaches the upper limit, some or all of reception packets  1206  may be erased. 
     In particular, in the power saving mode, main control unit  110  is unable to immediately process a received packet. Therefore, the received packet is accumulated in memory  1204  as reception packet  1206 . Thus, reception by receiver  1202  and storage in memory  1204  are repeatedly performed in the power saving mode. 
     Mode management module  1208  has main control unit  110  make mode transition from the power saving mode to the normal mode when at least any one of the number of reception packets  1206  stored in memory  1204 , a data amount of reception packet  1206  stored in memory  1204 , and a content of reception packet  1206  stored in memory  1204  satisfies a first condition. 
     Typically, the first condition includes a condition that the number of reception packets  1206  exceeds a prescribed number. Mode management module  1208  has main control unit  110  make mode transition from the power saving mode to the normal mode when the number of reception packets  1206  exceeds a prescribed number. The number of reception packets  1206  corresponds to the number of stored reception packets  1206 . 
     In another typical example, the first condition includes a condition that a data amount of reception packet  1206  exceeds a prescribed data amount. Mode management module  1208  has main control unit  110  make mode transition from the power saving mode to the normal mode when the data amount of reception packet  1206  exceeds a prescribed data amount. The data amount of reception packet  1206  corresponds to a total data amount of (one or a plurality of) stored reception packet(s)  1206 . The content of reception packet  1206  corresponds to a content of stored reception packet  1206 . 
     More specifically, mode management module  1208  gives a return command to main control unit  110  when the data amount of reception packet  1206  stored in memory  1204  satisfies the first condition. Main control unit  110  makes mode transition from the power saving mode to the normal mode in response to the return command from radio communication unit  120 . 
     Main control unit  110  may return in accordance with the number of received packets (whether or not a prescribed number of packets have been received). 
     Any interrupt signal can be used as such a return command. For example, an interrupt signal by means of a general-purpose input/output (GPIO), an interrupt signal (INTx) prepared in peripheral component interconnect (PCI) Express, or an interrupt signal prepared in a universal serial bus (USB) can be used for such an interrupt signal. Main control unit  110  can sense such an interrupt signal also in the power saving mode. Main control unit  110  is configured to sense a signal from radio communication unit  120  indicating mode transition (a return command or an interrupt signal) also in the power saving mode. 
     Main control unit  110  performs processing including reading by data reading module  1102  of reception packet  1206  stored in memory  1204  when it makes transition from the power saving mode to the normal mode, and after it performs the processing, it makes mode transition from the normal mode to the power saving mode. More specifically, data reading module  1102  of main control unit  110  accesses memory  1204  and reads reception packet  1206  stored in memory  1204 , and data processing module  1104  processes reception packet  1206  read by data reading module  1102 . 
     Main control unit  110  may erase read reception packet  1206  stored in memory  1204 . Specifically, data reading module  1102  of main control unit  110  may erase, after it reads a packet stored in memory  1204 , that read packet from memory  1204 . 
     Data reading module  1102  thus reads reception packet  1206  stored in memory  1204  when main control unit  110  makes mode transition from the power saving mode to the normal mode. Reception packet  1206  which has been processed by data processing module  1104  is basically erased from memory  1204 . Thereafter, main control unit  110  automatically makes transition from the normal mode to the power saving mode. Processing by main control unit  110  to return to the power saving mode does not require an operation by a user but is autonomously performed on condition that necessary processing is completed. 
     Processing of read reception packet  1206  performed by data processing module  1104  is not particularly limited, and any processing can be adopted. Data processing module  1104  may perform not only processing of read reception packet  1206  but also perform another type of processing additionally. When processing by data processing module  1104  is completed, information processing apparatus  100  returns to the power saving mode and waits for a return command from radio communication unit  120 . 
     Though  FIG. 5  shows an example in which memory  1204  is implemented as a part of radio communication unit  120 , it may be implemented as a part of main control unit  110  or implemented independently of radio communication unit  120  and main control unit  110 . 
     Though  FIG. 5  shows an example in which data reading module  1102  is implemented as a part of main control unit  110 , it may be implemented as a part of radio communication unit  120  or implemented independently of radio communication unit  120  and main control unit  110 . 
     Referring to  FIG. 6 , radio communication unit  120  periodically enters the reception awaiting state. When packet  300  arrives from another information processing apparatus  100  in this reception awaiting state, arriving packet  300  is received and stored in memory  1204  as reception packet  1206 . 
     Memory  1204  successively stores reception packet  1206  received by receiver  1202 . 
     When a data amount of reception packet  1206  stored in receiver  1202  satisfies the first condition, radio communication unit  120  (mode management module  1208 ) gives a return command  400  to main control unit  110 . When a plurality of areas for storing reception packets  1206  are prepared in advance as will be described later, whether or not to give return command  400  may be determined based on the number of areas where reception packets  1206  have already been stored among the plurality of areas (that is, how many storage areas have already been used among the storage areas prepared in advance). 
     Thus, “based on the data amount of the packet stored in memory  1204 ” in the present disclosure refers to a concept including not only an example of determination based on a total amount (a numeric value) of data of reception packets  1206  stored in memory  1204  but also an example of determination based on the number of stored reception packets  1206 . 
     Main control unit  110  makes mode transition from the power saving mode to the normal mode in response to return command  400 . Then, main control unit  110  (data reading module  1102  and data processing module  1104 ) performs processing including reading processing  402  by data reading module  1102  of reception packets  1206  stored in memory  1204 . When processing including reading processing  402  is completed (completion of processing  404 ), main control unit  110  returns from the normal mode to the original power saving mode. 
     In information processing apparatus  100  according to the present embodiment, radio communication unit  120  successively transmits and receives packet  300  and main control unit  110  is caused by radio communication unit  120  to intermittently perform processing of reception packet  1206 . By adopting such an operation in main control unit  110  and radio communication unit  120 , power consumption in information processing apparatus  100  as a whole can be reduced by allowing main control unit  110  to operate only for a required period while transmission and reception of packet  300  is continued. 
     [E. Data Format of Packet] 
     One example of a data format of packet  300  transmitted by information processing apparatus  100  will now be described with reference to  FIG. 7 . 
     The data format of packet  300  mainly includes a 802.11 header  302 , an action frame definition section  310 , a vendor-defined section  320 , and a payload section  330 . 
     Information processing apparatus  100  according to the present embodiment transmits and receives a packet under IEEE 802.11 standards. Therefore, 802.11 header  302  of packet  300  stores header information defined under the IEEE 802.11 standards. 
     Action frame definition section  310  stores information indicating that packet  300  is an action frame defined under the IEEE 802.11 standards. Packet  300  is a unique frame defined by the vendor and action frame definition section  310  stores information indicating that a packet is a unique frame defined by the vendor (which is also referred to as an organizationally unique identifier (OUI)). More specifically, action frame definition section  310  includes an OUI type area  312 , an OUI area  314 , and an OUI sub type area  316 . 
     Vendor-defined section  320  stores information necessary for data exchange according to the present embodiment. More specifically, vendor-defined section  320  includes a version area  322 , a command area  324 , and a hash value area  326 . Version area  322  stores identification information for ensuring compatibility of a data exchange protocol according to the present embodiment. Command area  324  stores information representing a type of packet  300  to be transmitted. Hash value area  326  stores a hash value as identification information for identifying packet  300 . A hash value stored in hash value area  326  is calculated from a payload (substantial data) stored in payload section  330 . A hash value stored in hash value area  326  is calculated in advance by information processing apparatus  100  which is a sender of packet  300 . 
     Since packet  300  should only be identified, unique information not dependent on a payload (substantial data) may be employed as identification information (hash value) unlike the disclosure described above. 
     Payload section  330  stores a substance of data to be carried by packet  300 . 
     [F. Processing for Filtering Reception Packet] 
     In information processing system  1  according to the present embodiment, each information processing apparatus  100  periodically transmits a packet. When a transmitted packet arrives during a reception awaiting period of any information processing apparatus  100 , that packet is received. Since such a communication procedure is adopted, identical packets from identical information processing apparatus  100  may be received a plurality of times. 
     In the present embodiment, only a packet which satisfies a second condition among packets received by information processing apparatus  100  is preferably stored in memory  1204 . Processing for selectively storing only a packet which satisfies the second condition is also referred to as “filtering processing” below. The second condition is also referred to as a “filtering condition.” Filtering processing performed on a reception packet will be described below. 
     Referring to  FIG. 8 , for example, it is assumed that receiver  1202  of information processing apparatus  100  chronologically receives a plurality of packets (a packet  01 , a packet  02 , a packet  03 , . . . ). 
     A filtering condition that only a packet which is not identical to a received in advance packet among a plurality of received packets is stored in memory  1204  is assumed in a typical example of filtering processing in information processing apparatus  100  according to the present embodiment. Namely, such a condition that a packet identical to a packet received in advance among a plurality of received packets is excluded from packets to be stored in memory  1204  is assumed. 
     With adoption of such a filtering condition, even though a plurality of packets including identical packets are received as shown in  FIG. 8 , only unique packets (three types of packets  01 ,  02 , and  03  in the example shown in  FIG. 8 ) are stored in memory  1204 . By applying the filtering processing, more types of reception packets can be stored even though a storage area is limited. 
     Memory  1204  of information processing apparatus  100  thus stores a packet which satisfies the filtering condition among packets received by receiver  1202 . 
     Referring to  FIG. 9 , radio communication unit  120  further includes a filtering processing module  1210  and a logical switch  1212 . Filtering processing module  1210  and logical switch  1212  are implemented by execution of firmware  127  by processor  126  of radio controller  124 . 
     Main control unit  110  includes a memory  1106  in addition to data reading module  1102  and data processing module  1104 . Memory  1106  is implemented by main memory  114  and/or non-volatile memory  116  ( FIG. 2 ). Memory  1106  is provided with a hash value table including a second hash value group  1226 . 
     Filtering processing module  1210  determines whether or not a packet received by receiver  1202  satisfies a filtering condition, and when it determines that the filtering condition is satisfied, it activates logical switch  1212  to logically couple receiver  1202  and memory  1204  to each other. A packet received by receiver  1202  is thus stored in memory  1204 . 
     Memory  1204  is provided with a reception packet buffer  1220  and a hash value table  1222 . Reception packet buffer  1220  temporarily stores a received packet. Hash value table  1222  includes a hash value used as one example of a filtering condition and calculated from substantial data included in a packet. The hash value represents one example of identification information for identification of a received packet and corresponds to a value representing data which constitutes the packet. 
     In the present embodiment, a hash value calculated from data which constitutes a packet received by receiver  1202  is used as a value representing the data which constitutes the packet. Without being limited to the hash value, any kind of information which allows distinction of a received packet from another packet may be employed as identification information. For example, a part or the entirety of substantial data itself included in a received packet may be employed as identification information. 
     Thus, a value representing data which constitutes a packet received by receiver  1202  (a hash value in this example) or at least a part of data as it is which constitutes the packet received by receiver  1202  may be used as identification information. 
     As described with reference to  FIG. 7  above, a hash value uniquely calculated from a payload (substantial data) stored in each packet  300  is added to packet  300  transmitted from each information processing apparatus  100 . A hash value used as the filtering condition, by being added by a sender of a packet of interest, thus simplifies and accelerates processing in radio communication unit  120 . Addition of a hash value by a sender of packet  300  is not a requirement, and a corresponding hash value may be calculated each time radio communication unit  120  receives a packet. 
     Filtering processing module  1210  determines matching between a hash value calculated from a packet received by receiver  1202  and a hash value stored in hash value table  1222 , by referring to hash value table  1222 . When the hash value calculated from the received packet matches with any hash value stored in hash value table  1222 , the received packet is excluded from packets to be stored in memory  1204  (for example, the received packet is discarded). 
     The filtering condition (that is, the second condition for a packet among reception packets to be stored in memory  1204 ) is determined based on identification information (a hash value in this example) of a packet received in advance by receiver  1202 . Such a filtering condition is stored in hash value table  1222 . 
     In the example shown in  FIG. 9 , hash value table  1222  includes two types of hash values as a typical example. Specifically, hash value table  1222  includes a first hash value group  1224  and a second hash value group  1226 A. 
     First hash value group  1224  includes a hash value corresponding to each reception packet stored in reception packet buffer  1220 . A hash value in first hash value group  1224  is dynamically updated in accordance with a status of a reception packet stored in reception packet buffer  1220 . More specifically, filtering processing module  1210  causes a hash value calculated from a reception packet stored in reception packet buffer  1220  to be reflected on first hash value group  1224  in hash value table  1222 . 
     By adopting processing for reflecting reception packet buffer  1220  on first hash value group  1224 , when a reception packet stored in reception packet buffer  1220  is read by data reading module  1102  of main control unit  110  and the reception packet buffer is emptied, first hash value group  1224  is also emptied. The hash value included in first hash value group  1224  thus reflects a status of a reception packet stored in reception packet buffer  1220 . 
     The filtering condition (that is, the second condition for a packet among reception packets to be stored in memory  1204 ) is thus at least partly determined based on a reception packet which is stored in memory  1204  but has not yet been read into main control unit  110 . A hash value of a reception packet held in reception packet buffer  1220  of memory  1204  corresponds to at least a part of a filtering condition and these hash values are stored in hash value table  1222  as first hash value group  1224 . 
     A content in second hash value group  1226  is set and updated by main control unit  110 . Second hash value group  1226  may mainly be accessed when main control unit  110  is in the normal mode. 
     In the example shown in  FIG. 9 , data processing module  1104  of main control unit  110  is responsible for addition and update of a hash value to be included in second hash value group  1226  in memory  1106 . Typically, data processing module  1104  adds a hash value calculated from a processed reception packet to second hash value group  1226  or updates any hash value included in second hash value group  1226  with a hash value calculated from the processed reception packet. 
     Second hash value group  1226  stored in memory  1106  of main control unit  110  is synchronized with second hash value group  1226 A included in hash value table  1222  stored in memory  1204  of radio communication unit  120 . More specifically, filtering processing module  1210  may access memory  1106  of main control unit  110  to copy second hash value group  1226  to memory  1204 . Alternatively, data processing module  1104  of main control unit  110  may copy second hash value group  1226  stored in memory  1106  of main control unit  110  to memory  1204 . 
     Radio communication unit  120  can thus process a packet received by receiver  1202  in accordance with a filtering condition determined by main control unit  110 , by reflecting a content in second hash value group  1226  stored in memory  1106  of main control unit  110  on hash value table  1222  stored in memory  1204  of radio communication unit  120 . 
     By adopting processing for adding a hash value as described above, a reception packet stored in reception packet buffer  1220  is processed by data processing module  1104  and erased from reception packet buffer  1220 . Then, a hash value which is identification information of the erased reception packet in reception packet buffer  1220  is transferred from first hash value group  1224  to second hash value group  1226 . Even though a reception packet stored in reception packet buffer  1220  is erased, a corresponding hash value continues to exist in hash value table  1222 . Therefore, even though a packet identical to an already received packet is received, redundant processing can be avoided. 
     Though second hash value group  1226  typically includes a hash value of a reception packet which has been processed by data processing module  1104 , limitation thereto is not necessarily required. For example, when advance information about a fraudulent or malicious packet received by another information processing apparatus  100  can be obtained, a hash value of a packet which should not be received may be included in second hash value group  1226  based on the advance information (use like a blacklist). 
     The description above provides an example in which a received packet is stored in memory  1204  only when a hash value is different from the hash value included in hash value table  1222 . In contrast, a received packet may be stored in memory  1204  only when a hash value matches with a hash value included in hash value table  1222  (use like a white list). 
     Thus, a filtering condition (that is, the second condition for a packet among reception packets to be stored in memory  1204 ) is at least partly determined by main control unit  110 . A filtering condition (a hash value in this example) determined by main control unit  110  is stored in hash value table  1222  as second hash value group  1226 . 
       FIG. 9  shows a configuration example in which first hash value group  1224  and second hash value group  1226  are included in hash value table  1222 . Without being limited as such, any one hash value group may be included in hash value table  1222 . The filtering condition may consist of a single condition. 
     There are two methods of (1) a method of dynamically generating a hash value based on at least a part of a received packet after reception of the packet and (2) a method of adding a hash value in a sender of the packet (that is, initially adding a hash value to the packet) as methods of obtaining a hash value as described above. Only one or both of (1) and (2) may be adopted. 
     The configuration example shown in  FIG. 9  shows a configuration in which second hash value group  1226  is stored in memory  1106  of main control unit  110  and first hash value group  1224  and second hash value group  1226 A (synchronized with second hash value group  1226 ) are stored in memory  1204  of radio communication unit  120 . A memory which stores a hash value, however, may be arranged at any position. For example, a memory may be arranged at any portion other than main control unit  110  and radio communication unit  120 . 
     Alternatively, second hash value group  1226  stored in memory  1106  of main control unit  110  does not have to be provided but second hash value group  1226  may directly be written into memory  1204  of radio communication unit  120  from main control unit  110 . Further alternatively, first hash value group  1224  stored in memory  1204  of radio communication unit  120  does not have to be provided but first hash value group  1224  and second hash value group  1226  may be stored in memory  1106  of main control unit  110 . 
     In general, memory  1204  of radio communication unit  120  is lower in total capacity than memory  1106  of main control unit  110 . Therefore, in some cases, a hash value used as a past filtering condition cannot permanently be stored. Therefore, a hash value stored in memory  1204  of radio communication unit  120  may be transferred at appropriate timing to memory  1106  of main control unit  110 . Furthermore, by returning to memory  1204  of radio communication unit  120 , a hash value transferred from memory  1204  of radio communication unit  120  to main control unit  110 , the hash value can also be used again in radio communication unit  120 . 
     [G. Processing Procedure] 
     A processing procedure involved with transmission and reception of packet  300  in information processing apparatus  100  according to the present embodiment will now be described with reference to  FIG. 10 . 
       FIG. 10  shows processing in main control unit  110  and radio communication unit  120  implementing information processing apparatus  100  as being distinguished. 
     Processor  126  of radio controller  124  included in radio communication unit  120  determines whether or not a cycle of transmission of packet  300  has come (step S 100 ). When the cycle of transmission of packet  300  has not yet come (NO in step S 100 ), processing in step S 100  is repeated. 
     When the cycle of transmission of packet  300  has come (YES in step S 100 ), radio communication unit  120  transmits packet  300  (step S 102 ). 
     In succession, processor  126  of radio communication unit  120  determines whether or not a reception cycle has come (step S 104 ). When the reception cycle has not yet come (NO in step S 104 ), processing hereafter is skipped and processing in step S 100  and subsequent steps is repeated. 
     When the reception cycle has come (YES in step S 104 ), processor  126  of radio communication unit  120  determines whether or not it has received any packet (step S 106 ). When it has received no packet (NO in step S 106 ), processor  126  of radio communication unit  120  determines whether or not a prescribed reception awaiting period since arrival of the reception cycle has elapsed (step S 108 ). 
     When the prescribed reception awaiting period since arrival of the reception cycle has not elapsed (NO in step S 108 ), processing in step S 106  and a subsequent step is repeated. In contrast, when the prescribed reception awaiting period since arrival of the reception cycle has elapsed (YES in step S 108 ), processing in step S 100  and subsequent steps is repeated. 
     When some packet has been received (YES in step S 106 ), processor  126  of radio communication unit  120  determines whether or not the received packet conforms to a prescribed format in which a packet with the format should be received (step S 110 ). When the reception packet does not conform to the prescribed format (NO in step S 110 ), radio communication unit  120  discards the received packet (step S 122 ). Then, processing in step S 100  and subsequent steps is repeated. 
     When the received packet conforms to the prescribed format (YES in step S 110 ), processor  126  of radio communication unit  120  determines whether or not a hash value of the received packet matches with any hash value included in first hash value group  1224  (step S 112 ). When the hash value of the received packet matches with any hash value included in first hash value group  1224  (YES in step S 112 ), radio communication unit  120  discards the received packet (step S 122 ). Then, processing in step S 100  and subsequent steps is repeated. 
     When the hash value of the received packet does not match with any hash value included in first hash value group  1224  (NO in step S 112 ), processor  126  of radio communication unit  120  determines whether or not the hash value of the received packet matches with any hash value included in second hash value group  1226  (step S 114 ). When the hash value of the received packet matches with any hash value included in second hash value group  1226  (YES in step S 114 ), radio communication unit  120  discards the received packet (step S 122 ). Then, processing in step S 100  and subsequent steps is repeated. 
     When the hash value of the received packet does not match with any hash value included in second hash value group  1226  (NO in step S 114 ), processor  126  of radio communication unit  120  has memory  1204  store the received packet as the reception packet and adds the hash value of the received packet to first hash value group  1224  (step S 116 ). Then, processor  126  of radio communication unit  120  determines whether or not a data amount of the reception packet stored in memory  1204  satisfies the first condition (in this example, whether or not a data amount of the reception packet exceeds a prescribed data amount) (step S 118 ). 
     When the data amount of the reception packet stored in memory  1204  does not satisfy the first condition (NO in step S 118 ), processing in the current reception cycle ends and processing in step S 100  and subsequent steps is repeated. 
     In the processing procedure described above, processing for determining whether or not a data amount of a packet stored in memory  1204  satisfies the first condition (step S 118 ) is exemplified. Without being limited as such, processing for determining whether or not the number of packets stored in memory  1204  satisfies the first condition (more specifically, whether or not the number of packets stored in memory  1204  exceeds a prescribed number) may be adopted as step S 118 . 
     Alternatively, as will be described later, processing for determining whether or not a content of a packet stored in memory  1204  satisfies the first condition (more specifically, whether or not a content of a packet stored in memory  1204  includes prescribed data) may be adopted as step S 118 . 
     Thus, in step S 118  described above, any one of determination as to whether or not a data amount of a reception packet exceeds a prescribed data amount, determination as to whether or not the number of reception packets exceeds a prescribed number, and determination as to whether or not a content of a reception packet includes prescribed data may be made, or a plurality of determinations among these may simultaneously be made. 
     In contrast, when a data amount of a reception packet stored in memory  1204  satisfies the first condition (YES in step S 118 ), processor  126  of radio communication unit  120  gives return command  400  to main control unit  110  (step S 120 ). Then, processing in the current reception cycle by radio communication unit  120  ends and processing in step S 100  and subsequent steps is repeated. 
     Main control unit  110  which has received return command  400  from radio communication unit  120  makes mode transition from the power saving mode to the normal mode (step S 200 ). Then, main control unit  110  reads reception packet  1206  stored in memory  1204  of radio communication unit  120  (step S 202 ). Then, main control unit  110  performs processing on read reception packet  1206  (step S 204 ). 
     Main control unit  110  determines whether or not reading of all reception packets  1206  stored in memory  1204  of radio communication unit  120  has been completed (step S 206 ). When reading of all reception packets  1206  stored in memory  1204  of radio communication unit  120  has not been completed (NO in step S 206 ), processing in step S 202  and subsequent steps is repeated. 
     When reading of all reception packets  1206  stored in memory  1204  of radio communication unit  120  has been completed (YES in step S 206 ), processor  126  of radio communication unit  120  erases all reception packets  1206  stored in memory  1204  of radio communication unit  120  and all hash values included in first hash value group  1224  (step S 208 ). 
     In succession, main control unit  110  adds a hash value of processed reception packet  1206  to second hash value group  1226  in memory  1106  based on a result of processing performed (S 210 ). When the number of hash values in second hash value group  1226  stored in memory  1106  has reached the upper limit, some or all of hash values already stored in second hash value group  1226  may be erased under a predetermined rule and then a new hash value may be added. A content in updated second hash value group  1226  stored in memory  1106  is reflected on hash value table  1222  stored in memory  1204  of radio communication unit  120 . 
     Then, main control unit  110  makes mode transition from the normal mode to the power saving mode (step S 212 ). A series of processing in radio communication unit  120  thus ends. 
     For the sake of convenience of description,  FIG. 10  shows a processing example in which main control unit  110  has reception packet  1206  and first hash value group  1224  in memory  1204  of radio communication unit  120  erased. Such data may be erased, however, by coordination between main control unit  110  and radio communication unit  120 . For example, when a command for erasure is given from main control unit  110  to radio communication unit  120 , radio communication unit  120  may perform processing for erasing data in memory  1204 . 
     In  FIG. 10  described above, in step S 202 , main control unit  110  may read at once, all reception packets  1206  stored in memory  1204 . 
     [H. Modification of Format Check and Filtering Processing] 
     In the description above, processing for avoiding redundant storage of identical packets by using identification information (for example, a hash value) for identifying a received packet is exemplified as processing for filtering a reception packet. Filtering processing according to the present embodiment includes processing for determining whether or not a received packet conforms to a prescribed format (see step S 110  in  FIG. 10 ). 
     By way of example of format check of a received packet, a content in action frame definition section  310  and vendor-defined section  320  (see  FIG. 7 ) included in the packet is used. More specifically, a condition that vendor-defined information expected to be received in advance is stored in action frame definition section  310  and/or a condition that a version or a command stored in vendor-defined section  320  is information expected to be received in advance may be adopted as the condition. 
     Any one piece of or any plurality of pieces of information can be used as the second condition (filtering condition) for determination as to whether or not a received packet is to be stored in memory  1204 . 
     For example, 802.11 header  302  (see  FIG. 7 ) of a received packet includes a media access control (MAC) address or an internet protocol (IP) address of a sender of the packet. Information for specifying the sender of the packet such as the MAC address or the IP address may be adopted as the filtering condition. In this case, such filtering processing as receiving only a packet from a sender having a specific address (white list) or not receiving a packet from a sender having a specific address (blacklist) can be applied. 
     A packet from an apparatus from which a packet was once received may be filtered out and not received (even though that packet is different in type) by referring to identification information specific to the apparatus such as a MAC address or identification information specific to a particular manufacturer such as an OUI. 
     Since a hash value calculated by a sender is added to packet  300  according to the present embodiment, identity between a hash value calculated by a reception side of packet  300  and the hash value added to packet  300  may be assessed. By assessing identity between the hash values, corruption or tampering of packet  300  in a process of transmission can be sensed. 
     Filtering processing may be performed based on combination of a plurality of factors. For example, a MAC address and a hash value may be combined with each other. 
     A sender of packet  300  may add identification information to payload section  330  of packet  300  and a reception side may determine whether or not to store received packet  300  in memory  1204  based on the identification information stored in payload section  330 . The second condition (filtering condition) for determining whether or not to store received packet  300  in memory  1204  may at least partly be determined based on identification information of a packet received in advance by receiver  1202 . 
     [I. Additional Configuration] 
     Some of additional configurations of information processing apparatus  1  according to the present embodiment will now be described. 
     (i1: Information on Time) 
     In information processing apparatus  100  according to the present embodiment, a packet received by radio communication unit  120  while main control unit  110  is in the power saving mode is processed at a later time by main control unit  110 . Therefore, timing of processing of the packet by main control unit  110  is later than timing of reception of the packet to be processed. Alternatively, main control unit  110  may not be able to obtain timing of reception of each packet. 
     In the present embodiment, when radio communication unit  120  receives a packet and the received packet is stored in memory  1204 , information representing timing of reception of each packet may be added. 
     Referring to  FIG. 11 , reception packet buffer  1220  in memory  1204  of information processing apparatus  100  may store, in association with a reception packet, a time stamp as being added as one example of time information which represents time of reception of each reception packet. 
     More specifically, when radio communication unit  120  receives a reception packet, it obtains a time stamp from a real time clock mounted on radio communication unit  120  at the timing of reception of the reception packet and adds the time stamp to the reception packet. 
     Receiver  1202  of radio communication unit  120  may thus provide a time stamp to a received packet. By adding a time stamp to each packet, even though main control unit  110  processes a packet at a later time, processing by making use of information such as reception timing can be performed. 
     More specifically, when main control unit  110  reads one reception packet or a plurality of reception packets, values of added time stamps may be compared among the read reception packets and a newer reception packet or an older reception packet may selectively be made use of. 
     (i2: Forced Startup Mode) 
     The description above provides an example in which when a data amount of reception packet  1206  stored in memory  1204  of radio communication unit  120  satisfies the first condition, main control unit  110  makes mode transition from the power saving mode to the normal mode. Processing for main control unit  110  to make mode transition from the power saving mode to the normal mode regardless of a data amount of reception packet  1206  stored in memory  1204 , however, may be performed. 
     More specifically, for example, such processing can be performed by including prescribed information (for example, information on a command) for having main control unit  110  make mode transition from the power saving mode to the normal mode in command area  324  (see  FIG. 7 ) in vendor-defined section  320  included in a packet. Receiver  1202  of radio communication unit  120  may determine whether or not a command for having main control unit  110  make mode transition from the power saving mode to the normal mode is included in command area  324  in vendor-defined section  320  when it checks a format of a received packet. 
     By adopting such a configuration, mode management module  1208  of radio communication unit  120  can have main control unit  110  make mode transition from the power saving mode to the normal mode regardless of the number of packets stored in memory  1204  and a data amount of a packet (depending on a content of a packet) stored in memory  1204 , in response to a packet received by receiver  1202  including instructions to make mode transition to the normal mode. When the content of reception packet  1206  stored in memory  1204  of radio communication unit  120  satisfies the first condition (for example, reception packet  1206  includes a prescribed command), main control unit  110  can make mode transition from the power saving mode to the normal mode. 
     In response to reception of a packet including such a command, main control unit  110  can return to the normal mode and perform necessary processing. For example, such an application that necessary notification processing is immediately performed when a packet for giving some kind of notification to a user is received is assumed. 
     [J. Advantages] 
     According to the present embodiment, even though main control unit  110  is in the power saving mode low in power consumption, receiver  1202  of radio communication unit  120  is able to receive a packet. When at least any one of the number of reception packets  1206  received by receiver  1202  and stored in memory  1204 , a data amount of a packet stored in memory  1204 , and a content of a packet stored in memory  1204  satisfies the first condition, main control unit  110  makes mode transition from the power saving mode to the normal mode and performs necessary processing, and makes again mode transition to the power saving mode. By making use of such mode transition of main control unit  110 , power consumption in information processing apparatus  100  can be reduced. 
     According to the present embodiment, it is also expected that identical packets are often received in a redundant manner. Even when such identical packets are received in a redundant manner, redundant storage of identical packets can be prevented to make information processing efficient. 
     While certain example systems, methods, devices, and apparatuses have been described herein, it is to be understood that the appended claims are not to be limited to the systems, methods, devices, and apparatuses disclosed, but on the contrary, are intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.