Abstract:
A portable electronic device and method manage battery-produced power without lowering sound quality for music and other sound effects. In the present invention, an operation clock of the CPU of the portable electronic device and a processing wait time for image drawing are dynamically controlled. When there is no sound emission request, the CPU runs at a low clock rate. Where there is a sound emission request, the CPU runs at a high clock speed. When the sound emission ends, the CPU returns to the low clock rate. A user senses no apparent change, as the CPU slows screen drawing speed at high clock speed and increases screen drawing speed at low clock speed.

Description:
FIELD OF THE INVENTION 
     This invention concerns a method, a portable electronic device, and an entertainment system in each of which power consumption can be economized by changing a CPU operation clock. 
     BACKGROUND OF THE INVENTION 
     A conventional memory card device, etc. (slave machine) that is used with being inserted into an information device or other master machine such as an entertainment system represented by a game machine has an interface for connecting it to the main unit (master machine) of the information device and a nonvolatile memory element for storing data. 
     FIG. 1A shows an example of the composition of the key parts of such a conventional memory card device. The conventional memory card  10  has a control unit  11  for controlling its operation, a connector  12  for connecting the card device to a terminal provided in a slot of an information device, and a nonvolatile memory  16  for storing data. Connector  12  and nonvolatile memory  16  are connected by the control unit  11 . 
     Control unit  11  may be, for example, a microprocessor (so labeled in the diagrams). Used as nonvolatile memory  16  is, for example, a flash memory such as an EEPROM (electrically erasable and programmable ROM). A microprocessor is also sometimes used for the connection interface with an information device, etc. as a control means for interpreting the protocol. 
     FIG. 1B shows the control elements in control unit  11  of conventional memory card  10 . 
     Thus a conventional memory card has a main unit connection interface for connecting with the main unit of the information device, etc., and a memory interface for inputting and outputting data to and from the nonvolatile memory. 
     A conventional video game device such as a home video game device has the function of storing game data, etc. in an auxiliary memory. The memory card device is also used as an auxiliary memory of such video game device. 
     FIG. 2 shows an example of a conventional video game device that uses a memory card as an auxiliary memory. Main unit  2  of this conventional video game device  1  has a disk loading unit  3 , which is accommodated in a roughly rectangular housing and in the center of which is mounted an optical disk, which is a recording medium on which video game application programs are stored, a reset switch  4  for resetting the game at will, a power switch  6 , and, for example, two slots  7 A and  7 B. 
     Memory card  10 , which is used as an auxiliary memory, is loaded in slots  7 A and  7 B, and for example, the results, etc. of a game played on the video game device  1  are sent from control means (CPU)  19  and are written into nonvolatile memory  16 . Multiple operation devices (controllers) not shown can also be connected to slots  7 A and  7 B, allowing multiple users to play competitive games, etc. simultaneously. 
     One could further give the function of executing a game and other programs to a slave machine that is connected using the memory card slot of an entertainment system, which serves as the master machine. That is, it is thought that after at least part of a program such as a game will be downloaded from the master machine, the program itself will be executed, and if the program is a game, it will be given the function of allowing the growth, etc. of the characters in the game. Such a portable electronic device (slave machine) can be used without modification as a portable information terminal, and by making communication with other devices easier, its range of applications can be expanded, thereby leading to the stimulation of new demand. 
     Removed from the master machine, such a portable electronic device drives, using an AC adaptor, a battery, etc., a central processing unit (CPU) that performs image processing, audio processing, etc. In particular, a battery is used if the portable electronic device is used portably. With a portable electronic device in such a case, it is important how efficiently the limited battery is used. 
     Meanwhile, among portable electronic devices, with those that employ a system in which the speaker is driven from the CPU via a digital/analog converter (DAC), if a musical piece or sound effects are to be emitted, a frequency at least twice that of the frequency to be emitted is required, so it is considered difficult to emit high-quality sounds without a rather high operation clock. 
     However, as stated above, in order to emit high-quality sound with a portable electronic device in which a CPU and DAC are directly connected, the CPU operation clock must be made high, creating the problem of high power consumption. 
     SUMMARY OF THE INVENTION 
     This invention, which was devised with the above problems in mind, provides, for the problems to be solved, a method and device that can use the battery of a portable electronic device efficiently without lowering the quality of the music, sound effects, and other sound that is emitted. 
     According to a first aspect of the present invention, there is provided a method of reducing power consumption, wherein a speaker is driven under a CPU instruction, and when audio sound is to be output, an operation clock with a CPU is varied by a sound emission request. The operation clock can be changed to either a high-speed mode or a medium-speed mode by the sound emission request, and otherwise it is set to a low-speed mode. 
     According to a second aspect of the present invention, there is provided a portable electronic device comprising a speaker driven by a CPU via a digital/analog converter, wherein a sound emission request is input to a bus controller that is linked to said CPU; and a close variation means controlled in accordance with the input to said bus controller, and an operation clock is made variable. 
     According to a third aspect of the present invention, an entertainment system is provided, which includes an entertainment device that has a program execution function and a portable electronic device that is detachably mounted on said entertainment device and includes an interface for making an electrical connection to said entertainment device, and in which the portable electronic device comprising a speaker driven by a CPU via a digital/analog converter, wherein sound emission requests are input to a bus controller that is linked to said CPU; a clock variation means controlled in accordance with the input to said bus controller, and wherein an operation clock is made variable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an example of the configuration of a conventional memory card; 
     FIG. 2 shows an example of a conventional video game device that employs a memory card as an auxiliary memory; 
     FIG. 3 is a flowchart for explaining the method of the present invention; 
     FIGS. 4A,  4 B and  4 C are front, plan, and rear views, respectively of the portable electronic device of the present invention; 
     FIG. 5 is a block diagram of the portable electronic device of the present invention; 
     FIG. 6 shows an arrangement of a control unit of the portable electronic device of the invention; 
     FIG. 7 is a plan view of the entertainment system of the present invention; 
     FIG. 8 is a perspective view of the entertainment system of the invention; and 
     FIG. 9 shows a relationship between a CPU clock frequency and operation time in the case where the CPU clock frequency of the portable electronic device is modified according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will hereinafter be described in detail. 
     A method according to a first aspect of the present invention will be described. 
     For both, long battery life of the portable electronic device and quality of the sound emission thereof, an operation clock of the CPU is controlled dynamically. That is, when there is no sound emission, the CPU is run at a low clock, and if there is a sound emission request (trigger) as an occasion for varying the CPU clock, the CPU will be switched to run at a high clock, and when the sound emission ends, the CPU will again be made to run at a low clock. Also, since simply changing the CPU clock will also change the speed of screen drawing, the processing is done so that one does not feel any apparent clock change; this is done by making the processing wait longer if the clock is high, and conversely, making the processing wait shorter if the clock is low. 
     In this specification, the “processing wait” means the processing time for maintaining the screen drawing constant and is also referred as “interrupt latency”. 
     Here, if it is the case of a portable electronic device, which will be described later on, a sound emission request may be a request for sound emission upon startup or a request for sound emission given by pressing an operation button, etc. In the case of a portable electronic device that has an indication means such as a cursor, one can cite cases in where request is made for a sound emission such as a sound to be emitted when an object is clicked with the cursor. Also, a sound emission request for emitting an alarm sound can be given in the case of, for example, a portable electronic device that has a built-in clock mechanism. 
     In the following, the first aspect of the invention will be described specifically with reference to the flowchart of FIG.  3 . Referring to FIG. 3, the process is shown, in which the CPU clock frequency and the image drawing speed are changed while a game is being played on a portable electronic device detachably attached to a game machine. 
     With the portable electronic device, as shown in step  1  (ST 1 ), the CPU handles the control of, for example, a key input for moving a game character, a screen processing such as drawing images of the background and characters, and sound emission information such as music or sound effects. In step  2  (ST 2 ), it is decided, during such control, whether there is a new sound emission request. 
     In step  2  (ST 2 ), if there is no new sound emission request, it is decided in step  3  (ST 3 ) whether the sound emission is currently taking place, and if it is, in step  4  (ST 4 ) the current processing wait is maintained, and the key input and screen processing, etc. in step  1  (ST 1 ) are continued. 
     If there is no new sound emission request and it is decided in step  3  (ST 3 ) that the sound emission is not currently taking place, the CPU clock is switched to the low-speed mode in step  5  (ST 5 ). 
     Also, for example in a portable electronic device, the clock of the CPU is normally run at a range from 32 kHz to 8 MHz. 
     If the CPU clock is switched to a low speed, because merely switching it to the low speed will also change the speed at which the screen drawing is done, it is necessary to control the screen drawing to keep the screen drawing constant so that there is no apparent change in the CPU clock. This processing is done in step  6  (ST 6 ) and step  4  (ST 4 ). More specifically, in step  6  (ST 6 ), an interrupt processing such as a time interrupt processing is executed, and the screen drawing processing time is set to a short time. Then, in step  4  (ST 4 ), control is executed so that the processing wait becomes a short time. Specifically, the prescribed interrupt time needed for the image drawing is set, and this interval of the interrupt time with respect to the interrupt time duration is made short in accordance with the CPU clock. After such processing is completed, the key input and screen processing, etc. of step  1  (ST 1 ) is continued. 
     Returning to step  2 , it will be now explained what happens if there is a new sound emission request. 
     It there is a sound emission request, following step  2  (ST 2 ), one proceeds to step  7  (ST 7 ), and the CPU clock is switched to a high-speed mode. Here, in the case of a portable electronic device, which is described below, the second emission request could be a sound emission request upon a startup or a sound emission request due to an operation button being pressed, and in the case of a game, the sound emission request could be a request to play sound effects or a musical piece requested in the game program. 
     As stated above, the CPU clock is switched to a high speed when there is a sound emission request. However, because such switching to a high speed also changes the speed of the screen drawing, it is necessary to control the screen drawing so that the screen drawing is kept constant and there is no change in the apparent CPU clock. This processing is done in step  8  (ST 8 ) and step  4  (ST 4 ). That is, in step  8  (ST 8 ), the interrupt processing such as a time interrupt processing is done, and the screen drawing processing time is set to a long time period. Then, in step  4  (ST 4 ), control is executed so that the processing wait becomes a long time. Specifically, the prescribed interrupt time needed for the image drawing is set, and this interval of the interrupt time with respect to interrupt time is made long in accordance with the CPU clock. After such processing is done, the key input and screen processing, etc. in step  1  (ST 1 ) is continued. 
     As described above, in the method of the present invention, the CPU clock is changed in accordance with sound emission requests and the drawing speed is controlled so that there is no apparent change. In the method of this invention, the CPU clock and the drawing speed need not be controlled by the software according to the above procedure. The control may also be executed by mechanical means. 
     Also, in the method of the present invention, the CPU clock may be changed in two or more stages. For example, it may be done in two or three stages. For example, the clock frequency may be set to 512 kHz and 4 MHz if the clock is changed in two stages, or 512 MHz, 4 MHz, and 1 MHz if the clock is changed in three stages. By thus changing the clock in three stages, an appropriate clock frequency can be set in accordance with the sound emission request, and the appropriate clock frequency can be set by the relationship between the sound emission request and the burden on the CPU. 
     Also, in the method of the present invention, a sound emission request was cited as the occasion (trigger) for changing the CPU clock, but the CPU clock may be changed when the necessity arises to do screen drawing that involves heavy processing. In such a case, the appropriate clock frequency can be selected from the relationship between the power consumption and the burden on the CPU by changing the clock in three stages. 
     A second embodiment of the present invention will be described. 
     A second aspect of the present invention will be described. 
     A portable electronic device, shown in FIGS. 4A-4C and FIGS. 5-6, has a speaker driven by a CPU via a digital/analog converter. Sound emission requests are input to a bus controller that is linked to the CPU, a clock variation unit is controlled in accordance with the input to the bus controller, and the operation clock is varied. 
     More specifically, an arrangement of the portable electric device will be described. FIGS. 4A-4C show a portable electronic device  400 , which is an embodiment of the portable electronic device of this invention. As a detachable portable electronic device, the potable electronic device  400  constitutes a part of the entertainment system shown in FIGS. 7 and 8. 
     As shown in FIGS. 4A through 4C, portable electronic device  400  includes a housing  401  and has an operation unit  420  for the input of various information, a display unit  430 , which consists of a liquid crystal display (LCD), etc., and a window  440  for performing wireless communication by, for example, infrared rays by a wireless communication unit. 
     Housed inside housing  401 , which consists of an upper shell  401   a  and a lower shell  401   b,  is a substrate on which are mounted memory elements, etc. The housing  401  is shaped so as to allow insertion into prescribed slots of the main unit of an entertainment system such as the video game device described below. 
     Window  440  is provided at the other end of housing  401 , which is formed in a roughly semicircular shape. Display unit  430  takes up about half the area of the upper shell  401   a,  which constitutes part of housing  401 , and is positioned near the window  440 . 
     Operation unit  420 , which has one or more operation buttons  421 ,  422  for performing an event input and making various selections, is formed in upper shell  401   a  in the same way as window  440 , and takes up about half the area of the side opposite the part where window  440  is positioned. Also, the operation unit  420  is positioned on a cover  410 , which is supported rotatably with respect to housing  401 . Here, operation buttons  421 ,  422  are arranged from the upper surface side to the lower surface side of cover  410  and pierce the cover  410 . The operation buttons  421 ,  422  can move in or out with respect to the upper surface part of cover  410  and are supported by the cover  410 . 
     Portable electronic device  400 , which is inside housing  401 , has a substrate positioned so as to be opposed to the cover  410 , and also has switch pressing units on the top of the substrate. With cover  410  closed, the switch pressing units are provided in positions corresponding to the positions of operation buttons  421 ,  422 . Thus when operation buttons  421 ,  422  are pressed, the switch pressing units press on pressing switches such as diaphragm switches. 
     As shown in FIG. 5, portable electronic device  400  has a control unit  441 , a connector  442 , an input unit  443 , a display  444 , a clock function unit  445 , a nonvolatile memory  446 , a speaker  447 , a wireless communication unit  448  and a wireless reception unit  449  as data transmission and reception means, a battery  450 , and a power source terminal  451  and a diode  452 , which constitute a power storage means. 
     The control unit  441  is constituted using, for example, a microprocessor. As shown in FIG. 6, control unit  441  includes a program memory  441   a,  which is a program storage means, a CPU core unit  441   b,  the bus controller unit  441   c,  and the clock variation unit  441   d.    
     In varying the CPU clock according to this invention, any trigger information (information that results in a request for sound emission) such as key operation  441   e  or a RTC (real-time clock)  441   f  that is input to the clock variation unit  441   d  via the bus controller  441   c,  and the CPU clock is changed by the clock variation unit  441   d.  An example of a request for sound emission by RTC  441   f  would be an alarm output instruction at fixed times. A PLL (phase-locked loop) may be used for the clock variation unit  441   d.  A crystal may also be used as clock variation unit  441   d.  However, the crystal will then be positioned outside the control unit  441 . 
     Connector  442  is constituted for connecting to the slot of another information device. For example, connector  442  has a data communication function for sending and receiving data to and from, for example, a video game device. 
     Input unit  443  has operation buttons, etc. for operating a stored program. 
     Display  444  has a liquid crystal display (LCD), etc., which is a display means for displaying various information. 
     Clock function unit  445  is constituted so as to display the time; for example, it can perform time display to display  444 . 
     Nonvolatile memory  446  is an element for storing various data. For example, one can use for nonvolatile memory  446  a semiconductor memory element, such as a flash memory, in which the stored static lingers even if the power is cut off. 
     Because portable electronic device  400  has battery  450 , one can use as nonvolatile memory  446  a static random access memory (SRAM), which allows data to be input and output at high speed. 
     Also, the provision of battery  450  makes it possible for the portable electronic device  400  to operate independently even in the state in which it is removed from the video game device main unit. 
     Battery  450  may be, for example, a rechargeable secondary battery. With portable electronic device  400  inserted into the video game device, battery  450  is supplied with power from the video game device. In this case, a power source terminal  451  is connected to the connection terminal of battery  450  via a reserve current prevention diode  452 , and power is supplied when the portable electronic device  400  is connected to the video game device main unit. 
     Wireless communication unit  448  is a part that performs data communication with another memory card, etc. by infrared rays, etc. 
     Wireless reception means  449  is a part that has an antenna and a demodulation circuit, etc. That is, it is the part that receives various data that is transmitted by wireless broadcasting. This wireless reception unit  449  may have a memory for temporarily storing the broadcast data that is received. 
     Speaker  447  is a sound emission means that emits sound in accordance with the program, etc. 
     All of the above parts are connected to control unit  441  and operate under the control of control unit  441 . 
     If for example the power of portable electronic device  400  is turned on, control unit  441  (microprocessor) shown in FIG. 5 performs an operation confirmation and other initialization of portable electronic device  400  as a whole, and then executes the application program stored in program memory  441   a.  By execution of this application program, control unit  441  controls display  444 , speaker  447 , etc. in accordance with the input from the user and consequently controls the display of images and the generation of sound effects and music. 
     In the portable electronic device of this invention, the above-described method of the present invention is carried out by the control unit  441 . This procedure will hereinafter be described. In the following description, each step shown in FIG. 3 is cited in parentheses. 
     During the execution of a program stored in the program memory, for example, it is decided by control unit  441  whether there is a new sound emission request (ST 2 ). If there is no new input information, it is decided whether a sound is currently being emitted (ST 3 ), and if the sound is being emitted, the current processing wait is maintained (ST 4 ), and the key input and the screen processing, etc. is continued (ST 1 ). 
     If it is decided that no sound is currently being emitted, the CPU clock is switched to the low-speed mode (ST 5 ). The switchover of the CPU clock to the low-speed mode is done, as described above, by clock variation unit  441   d,  such as a PLL or crystal oscillator, that can be used with the portable electronic device  400 . 
     Also, for example in the portable electronic device, the clock of the CPU is normally run at a range from 32 kHz to 8 MHz. 
     If the CPU clock is switched to a low speed, because merely switching it to the low speed will also change the speed at which the screen drawing is done, it is necessary to control the screen drawing to keep it constant, with no apparent change in the CPU clock. In this processing, the interrupt processing such as the time interrupt processing is done, and the screen drawing processing time is set to a short time (ST 6 ). Then control is executed so that the processing wait becomes a short time (ST 4 ). Specifically, the prescribed interrupt time needed for the image drawing is set, and the interval of the interrupt time is made shorter in accordance with the CPU clock as compared with respect to the interrupt time. After such processing is done, key input and screen processing, etc. is continued (ST 1 ). 
     It will be described next the case where there is a sound emission request. 
     If there is a sound emission request, the CPU clock is switched to a high-speed mode. The switching to the high-speed mode is done by clock control unit  441   d,  such as a PLL or crystal oscillator. Here, the sound emission request could be a sound emission request due to an operation button being pressed, or the sound emission request could be a request to play sound effects or a musical piece requested in the game program. 
     As stated above, the CPU clock is switched to the high speed when there is a sound emission request. However, because the switching to the high speed also changes the speed of the screen drawing, it is necessary to control the screen drawing so that the screen drawing is kept constant and there is no change in the apparent CPU clock. In this processing, first, interrupt processing such as the time interrupt processing is done, and the screen drawing processing time is set to a long time. Then control is executed so that the processing wait becomes a long time (ST 8  and ST 4 ). Specifically, the prescribed interrupt time needed for the image drawing is set, and the interval of the interrupt time is made longer in accordance with the CPU clock as compared with respect to the interrupt time. After such processing is done, key input and screen processing, etc. is continued (ST 1 ). 
     As described above, this invention provides a device that changes the CPU clock in accordance with sound emission requests and controls the drawing speed so that there is no apparent change. In the portable electronic device of this invention, the CPU clock and the drawing speed can be controlled by hardware as in the above procedure, but they can also be controlled by software means. 
     Also, in the portable electronic device of this invention, the CPU clock frequency may be changed in two or more stages. Two or three stages are preferable. Specifically, it may be changed at 512 kHz and 4 MHz if the clock frequency is changed in two stages, or 512 kHz, 4 MHz, and 1 MHz if the clock frequency is changed and in three stages. 
     Also, in the portable electronic device of this invention, a sound emission request was cited as the occasion (trigger) for changing the CPU clock, but the CPU clock may be changed when the necessity arises to do screen drawing that involves heavy processing. 
     A third aspect of the present invention will be described. 
     An entertainment system of the present invention has an entertainment device that has a program execution function and a portable electronic device that is detachably mounted on the entertainment device and has an interface for making an electrical connection to the entertainment device. In the entertainment system the portable electronic device is constituted so that the speaker is driven by the CPU via a digital/analog converter, sound emission requests are input to a bus controller that is linked to CPU, a clock variation unit is controlled in accordance with the input to the bus controller, and the operation clock is made variable. 
     An arrangement of the entertainment system of the present invention will be described. 
     As shown in FIGS. 7 and 8, the entertainment system of this invention includes a video game device  301  and the portable electronic device  400 , which can be attached to and detached from the video game device  301  and performs data communication with the video game device  301 . In the entertainment system, the video game device  301  is constituted as the master machine, and portable electronic device  400  is constituted as a slave machine. 
     As shown in FIGS. 7 and 8, the video game device  301  reads an application program recorded on a recording medium and executes the program in accordance with instructions from the user (game player). For example, the progress, display and audio control of the game are done mainly by execution of the game. 
     A main unit  302  of video game device  301  has a disk loading unit  303 , which is accommodated in a roughly rectangular housing in the center of which is loaded an optical disk, such as a CD-ROM, which is a recording medium for supplying a video game and other application programs, a reset switch  304  for resetting the video game at will, a power switch  305 , a disk operation switch  306  for performing the operation of mounting the optical disk, and two slots  307 A and  307 B. 
     In video game device  301 , the application program is not only supplied from a recording medium but is supplied via a communication circuit. 
     The portable electronic device  400  and controller  320  can be connected to slots  307 A and  307 B. A memory card system can also be connected to slots  307 A and  307 B. 
     Controller  320  has first and second operation units  321  and  322 , a left button  323 L and a right button  323 R, a start button  324 , a selection button  325 , operation units  331  and  332  that are capable of analog operation, an operation mode selector switch  333  that selects the operation mode of operation units  331  and  332 , and a display unit  334  for displaying the selected operation mode. Also, provided inside controller  320  is a vibration mechanism (not shown). The vibration mechanism vibrates controller  320  in accordance with, for example, the progress of the video game. The controller  320  is electrically connected by a connector  326  to slot  307 B of the main unit  302 . 
     For example, by connecting two controllers  320  to slots  307 A and  307 B, two game players can share this entertainment system. For example, a competitive game can be played by two game players. Slots  307 A and  307 B are not limited to the two as is the case here. 
     In an entertainment system constructed in this way, the portable electronic device  400  can be detachably attached to the entertainment system. 
     The appearance of video game device  301  and portable electronic device  400  is constituted as described above. 
     The entertainment system of this invention has portable electronic device  400  of the above discussed configuration, and in the portable electronic device, the CPU clock can be varied as explained above. 
     According to the present invention, in the case of the portable electronic device  400 , the power consumption when waiting can be reduced, for example, to about one-sixth (from 3.2 mA to 550 μA). 
     Also, the change in the continuous operation time with respect to the change in the clock frequency of the CPU was measured using portable electronic device  400  of this invention. The results are presented in Table 1 below. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Operation frequency versus operation time 
               
             
          
           
               
                 Operation 
                 Power 
                 Continuous operation 
               
               
                 frequency (kHz) 
                 consumption (mA) 
                 time (hr) 
               
               
                   
               
             
          
           
               
                 32 
                 0.46 
                 330.0 
               
               
                 62.5 
                 0.82 
                 180.0 
               
               
                 125 
                 1.10 
                 120.0 
               
               
                 250 
                 1.38 
                 90.0 
               
               
                 500 
                 1.70 
                 65.0 
               
               
                 1000 
                 2.10 
                 45.0 
               
               
                 2000 
                 3.20 
                 19.0 
               
               
                 4000 
                 5.50 
                 4.0 
               
               
                   
               
             
          
         
       
     
     Table 1 shows the operation frequency (Hz), current consumption (mA), and continuous operation time (hr). For example, in the case of an operation frequency of 500 kHz, 1 MHz, and 4 MHz, the current consumption and continuous operation time were, respectively, 1.70 (mA), 65.0 (hr), 2.10 (mA), 45 (hr), and 5.50 (mA), 4.0 (hr). That is, it is clear that there is an up to 16-fold difference in operation time between a 500-kHz operation frequency and a 4-MHz operation frequency. 
     With this invention, for example, by changing the clock frequency of the CPU in accordance with sound emission requests, the lifetime of the battery used with the portable electronic device can be significantly prolonged, with no reduction in the quality of sound emission such as sound effects and music.