Abstract:
A power usage method is provided for using power supplied from a first device at a second device. The power usage method includes causing the second device to perform an initialization process to obtain a value of a current used when consuming the power at a voltage that is a minimum prerequisite for the second device to perform a predetermined process; and causing the second device to execute the predetermined process while consuming the power in a manner that the current does not exceed the obtained value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is based upon and claims the benefit of priority under 35 USC 120 and 365(c) of PCT application JP2008/003704 filed in Japan on Dec. 11, 2008, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention is related to a method of supplying power from a master device to a slave device via an interface such as USB and using the power at the slave device, etc. 
       BACKGROUND 
       [0003]      FIGS. 11 and 12  illustrate the ranges of power supplied to a slave device in an old specification and a new specification, respectively. 
         [0004]    In recent years, USB (Universal Serial Bus) has become prevalent as an interface for connecting two devices. For example, various devices may be connected to a personal computer by USB, such as a printer, a digital camera, a mobile phone unit, a floppy disk drive, a portable audio-player, a PDA (Personal Digital Assistant), and a USB memory. 
         [0005]    According to the USB, data is exchanged between two devices, and also power is supplied from a host device (a higher-level device; typically a personal computer or a USB hub) to a slave device (a lower-level device). Therefore, with the use of the USB, a secondary battery provided in the slave device may be charged by supplying power from the host device. 
         [0006]    Non-patent document 1 defines specifications for supplying power to a slave device by the USB. 
         [0007]    In a specification (old specification) previous to this specification (new specification), power needs to be supplied by the VBus from the host device to the slave device within the range of the “existing region” indicated in  FIG. 11 . 
         [0008]    However, with the new specification, it is possible to supply power within the range of the “extended region” indicated in  FIG. 11 . Alternatively, when data communications are also performed between the host device and the slave device, it is also possible to supply power within the ranges of the “high speed extended region” and the “full speed/low speed extended region” indicated in  FIG. 12 , according to the transfer mode. As described above, in the new specification, restrictions relevant to supplying power are mitigated. 
         [0009]    Non-patent document 1: “Battery Charging Specification Revision 1.0”, May 8, 2007, USB Implementers Forum, Inc. 
         [0010]    However, because the restrictions have been mitigated as described above, there are cases where the slave device does not receive power supplied as expected. When the slave device does not receive power, the slave device may not normally execute some processes. 
         [0011]    For example, assuming that the slave device does not recognize being connected to the master device unless the slave device receives a voltage of four volts or more, the slave device does not operate properly when a voltage of only two volts is applied to the slave device. 
       SUMMARY 
       [0012]    According to an aspect of the present invention, a power usage method is provided for using power supplied from a first device at a second device, the power usage method including causing the second device to perform an initialization process to obtain a value of a current used when consuming the power at a voltage that is a minimum prerequisite for the second device to perform a predetermined process; and causing the second device to execute the predetermined process while consuming the power in a manner that the current does not exceed the obtained value. 
         [0013]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  illustrates an example of a personal computer and a USB device being connected to each other; 
           [0015]      FIG. 2  illustrates an example of a hardware configuration of the personal computer; 
           [0016]      FIG. 3  illustrates examples of functional configurations of the personal computer and the USB device; 
           [0017]      FIG. 4  illustrates an example of a hardware configuration of the USB device; 
           [0018]      FIG. 5  illustrates an example of a voltage/current table TLA; 
           [0019]      FIG. 6  illustrates an example of a configuration of a training unit; 
           [0020]      FIG. 7  is a sequence diagram for describing the overall flow of a process performed when the personal computer and the USB device are connected; 
           [0021]      FIG. 8  illustrates an example of a voltage/current table TLB; 
           [0022]      FIG. 9  illustrates an example of a voltage/current table TLC; 
           [0023]      FIG. 10  illustrates another example of the personal computer and the USB device being connected to each other; 
           [0024]      FIG. 11  indicates ranges used for supplying power to a slave device in an old specification and a new specification; and 
           [0025]      FIG. 12  indicates ranges used for supplying power to a slave device in an old specification and a new specification. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Preferred embodiments of the present invention will be explained with reference to accompanying drawings. 
         [0027]      FIG. 1  illustrates an example of a personal computer  1  and a USB device  2  being connected to each other.  FIG. 2  illustrates an example of the hardware configuration of the personal computer  1 .  FIG. 3  illustrates examples of the functional configurations of the personal computer  1  and the USB device  2 .  FIG. 4  illustrates an example of the hardware configuration of the USB device  2 . 
         [0028]    The personal computer  1  illustrated in  FIG. 1  has an USB (Universal Serial Bus) interface. 
         [0029]    The USB device  2  is, for example, a portable device provided with a USB interface, such as a mobile phone unit, a portable audio-player, and a PDA (Personal Digital Assistant). 
         [0030]    The personal computer  1  and the USB device  2  are connected by a USB cable, and perform communications with each other. Furthermore, the personal computer  1  supplies power to the USB device  2 . In the following example, the versions of USB are USB 2.0 and 1.0. 
         [0031]    As illustrated in  FIG. 2 , the personal computer  1  includes a control device  10   a,  a RAM (Random Access Memory)  10   b,  a ROM (Read Only Memory)  10   c,  a hard disk  10   d,  a liquid crystal display  10   e , a keyboard  10   f,  a pointing device  10   g,  and a USB controller  10   h.    
         [0032]    The control device  10   a  is, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and the control device  10   a  executes programs stored in the RAM  10   b  or the ROM  10   c.  When the control device  10   a  is an MPU, the RAM  10   b  and the ROM  10   c  may be integrally combined with the control device  10   a.    
         [0033]    The keyboard  10   f  and the pointing device log are devices used by the user for inputting commands and data into the personal computer  1 . 
         [0034]    The liquid crystal display  10   e  displays various images such as a desktop, windows, and dialogue boxes. 
         [0035]    The USB controller  10   h  is an IC (Integrated Circuit) for controlling the USB. 
         [0036]    As illustrated in  FIG. 3 , the ROM  10   c  stores programs for implementing functions of a voltage current table storage unit  101 , a minimum voltage inquiry unit  102 , a minimum voltage report receiving unit  103 , a supply current determining unit  104 , a maximum current report unit  105 , and a supply current control unit  106 . These programs are executed by the control device  10   a.  These programs may be provided as the BIOS (Basic Input/Output System) or as a driver of the OS (Operating System). In the latter case, the driver is stored in the hard disk  10   d.    
         [0037]    As illustrated in  FIG. 4 , the USB device  2  includes a CPU  20   a,  a RAM  20   b,  a ROM  20   c,  a power unit  20   d,  a USB controller  20   e,  and a training unit  20   f.  Furthermore, the USB device  2  includes various hardware components depending on the type of the USB device  2 . For example, if the USB device  2  is a mobile phone unit, the USB device  2  includes a wireless circuit, an antenna, a liquid crystal display, operation buttons, a voice processing circuit, a digital camera, a microphone, a speaker, and a flash memory. 
         [0038]    The USB controller  20   e  is an IC for controlling the USB. The power unit  20   d  includes a secondary battery and a charge control circuit. The secondary battery is charged by power supplied from the personal computer  1  via a USB cable. Furthermore, the secondary battery supplies power to the respective units of the USB device  2 . The charge control circuit controls the operation of charging the secondary battery, and prevents overcharging. 
         [0039]    The ROM  20   c  stores programs for implementing functions of a minimum voltage storing unit  201 , a minimum voltage command receiving unit  202 , a minimum voltage reporting unit  203 , and a maximum current report receiving unit  204  illustrated in  FIG. 3 . These programs are executed by the CPU  20   a.  Details of the training unit  20   f  are given below. 
         [0040]      FIG. 5  illustrates an example of a voltage/current table TLA, and  FIG. 6  illustrates an example of a configuration of the training unit  20   f.    
         [0041]    Details are given of processes performed by the respective units in the personal computer  1  and the USB device  2  illustrated in  FIG. 3 , and processes performed by the power unit  20   d  and the training unit  20   f  illustrated in  FIG. 4 . 
         [0042]    In the personal computer  1 , the voltage current table storage unit  101  stores the voltage/current table TLA. As illustrated in  FIG. 5 , the voltage/current table TLA indicates the relationship between the voltage applied to the USB device  2  and the current supplied to the USB device  2 . Contents of the voltage/current table TLA are determined according to characteristics of the USB controller  10   h,  and are stored in the voltage current table storage unit  101 . 
         [0043]    The voltage/current table TLA indicates the relationship between the voltage and the current when data communications are not performed after the personal computer  1  is connected to the USB device  2 . A case where data communications are performed is described below. 
         [0044]    When the USB device  2  is connected to the personal computer  1 , the minimum voltage inquiry unit  102  sends a command (hereinafter, “command  3 A”) to the USB device  2 , requesting the USB device  2  to send a response indicating a minimum requisite voltage (hereinafter, “minimum voltage Eb”). 
         [0045]    The minimum voltage storing unit  201  of the USB device  2  stores the, minimum requisite voltage, i.e., the minimum voltage Eb, required for the USB device  2  to charge itself. 
         [0046]    The minimum voltage command receiving unit  202  receives the command  3 A from the personal computer  1 . 
         [0047]    When the command  3 A is received, the minimum voltage reporting unit  203  sends, to the personal computer  1 , response data  3 B indicating the minimum voltage Eb stored in the minimum voltage storing unit  201 . 
         [0048]    In the personal computer  1 , the minimum voltage report receiving unit  103  receives the response data  3 B from the USB device  2 . 
         [0049]    The supply current determining unit  104  searches the voltage/current table TLA (see  FIG. 5 ) for the current value corresponding to the minimum voltage Eb indicated in the response data  3 B that has been received. The supply current determining unit  104  determines the value of the search found current as the current to be supplied to the USB device  2  (hereinafter, “maximum current Ib”). For example, when the minimum voltage Eb is 4.0 V, the maximum current Ib is determined as 1240 mA. 
         [0050]    The maximum current report unit  105  sends, to the USB device  2 , report data  3 C indicating the determined maximum current Ib. 
         [0051]    The supply current control unit  106  controls the USB controller  10   h  so that the power corresponding to the determined maximum current Ib is supplied. 
         [0052]    In the USB device  2 , the maximum current report receiving unit  204  receives the report data  3 C from the personal computer  1 . 
         [0053]    According to the above processes, a current that is less than or equal to the maximum current Ib is supplied to the USB device  2 , so that the secondary battery is charged. 
         [0054]    The charge control circuit of the power unit  20   d  charges the secondary battery with a voltage that is greater than or equal to the minimum voltage Eb. The current that flows to the secondary battery is controlled so as not to exceed the maximum current Ib reported from the personal computer  1 . 
         [0055]    The charge control circuit of the power unit  20   d  may control the current flowing to the secondary battery so as not to exceed the current detected by the training unit  20   f  of  FIG. 4 . 
         [0056]    The training unit  20   f  measures the current required for obtaining the minimum voltage Eb at the USB device  2  (hereinafter, “maximum current Ih”), and performs a process for sending a report to the power unit  20   d.    
         [0057]    As illustrated in  FIG. 6 , the training unit  20   f  includes a variable current consumption circuit  20   f   1  and a voltage detection circuit  20   f   2 . As described below, the training unit  20   f  is used for performing a test to detect the relationship between the voltage and the current when performing a predetermined process (in the present embodiment, a charging process). 
         [0058]    When the USB device  2  is connected to the personal computer  1  and a current is supplied from the personal computer  1  to the USB device  2 , part of the current is supplied to the variable current consumption circuit  20   f   1  by gradually increasing the amount of the current, to be consumed by the variable current consumption circuit  20   f   1 . The variable current consumption circuit  20   f   1  is a circuit used for testing (training). The resistance of the variable current consumption circuit  20   f   1  is the same as the resistance when the secondary battery of the power unit  20   d  is being charged. 
         [0059]    The amount of current supplied to the variable current consumption circuit  20   f   1  is controlled by the CPU  20   a.    
         [0060]    The voltage detection circuit  20   f   2  continues measuring the voltage while a current is being supplied to the variable current consumption circuit  20   f   1 . When the voltage detection circuit  20   f   2  detects that the measured voltage has reached the minimum voltage Eb, the voltage detection circuit  20   f   2  reports this to the CPU  20   a.    
         [0061]    When the report is received from the voltage detection circuit  20   f   2 , the CPU  20   a  sets, as the maximum current Ih, the current supplied to the variable current consumption circuit  20   f   1  at the corresponding time point (i.e., the time point at which the voltage applied to the variable current consumption circuit  20   f   1  reaches the minimum voltage Eb). Then, the CPU  20   a  reports the determined maximum current Ib to the power unit  20   d.    
         [0062]    The charge control circuit of the power unit  20   d  controls the current supplied to the secondary battery so as not to exceed the maximum current Ih obtained by the training unit  20   f  and the CPU  20   a.  Accordingly, the secondary battery is charged by a voltage that is greater than or equal to the minimum voltage Eb. 
         [0063]      FIG. 7  is a sequence diagram for describing the overall flow of a process performed when the personal computer  1  and the USB device  2  are connected. 
         [0064]    A description is given of the overall flow of a process performed by the personal computer  1  and the USB device  2  with reference to  FIG. 7 . 
         [0065]    Referring to  FIG. 7 , when the USB device  2  is connected to the personal computer  1 , the personal computer  1  and the USB device  2  recognize that they are connected to each other as in the conventional technology, and makes various settings (configuration) relevant to hardware and software (# 301 , # 401 ). 
         [0066]    Then, the personal computer  1  sends a command  3 A to the USB device  2  to inquire the minimum voltage (# 302 ). When the USB device  2  receives the command  3 A (# 402 ), the USB device  2  sends the response data  3 B indicating the minimum voltage Eb to the personal computer  1  (# 403 ). 
         [0067]    When the response data  3 B is received (# 303 ), the personal computer  1  searches for the maximum current Ib corresponding to the minimum voltage Eb from the voltage/current table TLA (see  FIG. 5 ), and sends the report data  3 C to the USB device  2  to report the maximum current Ib (# 304 ). 
         [0068]    Then, the personal computer  1  supplies power to the USB device  2  (# 305 ). 
         [0069]    The USB device  2  receives the power (# 405 ), calculates the maximum current Ih (# 306 ), and charges the secondary battery with the maximum current Ih being the higher limit of current (# 407 ). 
         [0070]    According to the present embodiment, in a specification where restrictions relevant to supplying power are expanded, the USB device  2  is operated more reliably compared to the conventional technology. 
         [0071]      FIG. 8  illustrates an example of a voltage/current table TLB,  FIG. 9  illustrates an example of a voltage/current table TLC, and  FIG. 10  illustrates another example of the personal computer  1  and the USB device  2  being connected to each other. 
         [0072]    When the personal computer  1  and the USB device  2  are to perform data communications after being connected to each other, the relationship between the voltage and the current is different from that indicated in the voltage/current table TLA according to the communication speed. 
         [0073]    Accordingly, a voltage/current table TLB for a full speed mode and a low speed mode and a voltage/current table TLC for a high speed mode are provided in the voltage current table storage unit  101  in advance. 
         [0074]    When the transfer mode is determined to be the full speed mode or the low speed mode according to the configuration, the personal computer  1  uses the voltage/current table TLB instead of the voltage/current table TLA to determine the maximum current Ib. When the transfer mode is determined to be the high speed mode, the personal computer  1  uses the voltage/current table TLC instead of the voltage/current table TLA to determine the maximum current Ib. 
         [0075]    In the present embodiment, the training unit  20   f  is provided in the USB device  2  as illustrated in  FIG. 6 . However, as illustrated in  FIG. 10 , the training unit  20   f  may be provided in a connector of the USB device  2  provided on a USB cable  4  connecting the personal computer  1  and the USB device  2 . However, in this case, the connector provided on the USB cable  4  on the USB device  2  side is provided with a controller for controlling the current supplied to the variable current consumption circuit  20   f   1  and a controller for controlling the current supplied to the USB device  2  so that the maximum current Ih is supplied to the USB device  2 . 
         [0076]    Functions of the voltage current table storage unit  101  and the supply current control unit  106  illustrated in  FIG. 3  may also be provided in the USB hub. In this case, the current to be output is controlled for each USB device  2  that is connected. 
         [0077]    Furthermore, the overall configuration or configurations of the respective units of the personal computer  1  and the USB device  2 , the process contents, the process order, and configurations of the tables may be appropriately modified according to the purpose of the present invention. 
         [0078]    According to one embodiment of the present invention, in a specification where restrictions relevant to power supply are expanded, the device that receives power is capable of operating more reliably compared to the conventional technology. 
         [0079]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.