Patent Publication Number: US-2011076945-A1

Title: Methods for Controlling a Main Clock Source Shared Between Different Wireless Communication Modules and Apparatuses Using the Same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part (CIP) of U.S. patent application entitled “Methods for controlling a main clock source shared between different wireless communications modules and apparatuses using the same,” Ser. No. 12/719,088 filed on Mar. 8, 2010, which claims the benefit of U.S. Provisional Application No. 61/246,564 filed 2009 Sep., 29 and entitled “Methods for controlling a main clock source shared between different wireless communications modules and apparatuses using the same”. The entire contents of both are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method and an apparatus for controlling a main clock source, and more particularly to a method and an apparatus for controlling a main clock source shared between different wireless communications modules in a coordinated manner. 
     2. Description of the Related Art 
     With the development of wireless communications technology, mobile electronic devices may be provided with more than one wireless communications service, such as Bluetooth, Wireless Fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX) wireless communications service, and so on. However, the clock frequencies required by the wireless communications services are generally different. When using multiple clock sources, each for a corresponding wireless communications service, in the mobile electronic device, battery power consumption is increased. Therefore, a method and an apparatus for controlling a main clock source shared between different wireless communications modules is highly required to reduce battery power consumption. 
     BRIEF SUMMARY OF THE INVENTION 
     Wireless communications modules and methods executed by a wireless communications module for controlling a clock source shared with a wireless telephony communications module are provided. An embodiment of a wireless communications module coexisting with a wireless telephony communications module comprises a radio frequency (RF) module, a MODEM, a clock generator and distributor and a system control logic. The system control logic issues an external interrupt (EINT) signal to the wireless telephony communications module for activating a clock source via the wireless telephony communications module. When the clock source is activated, the clock generator and distributor receives a reference clock from the activated clock source, converts the reference clock into one or more internal clocks and drives the internal clock or clocks to the RF module and the MODEM for synchronization therebetween. 
     An embodiment of a method executed by a wireless communications module for controlling a clock source shared with a wireless telephony communications module comprises: issuing, by the wireless communications module, an external interrupt (EINT) signal to the wireless telephony communications module for activating the clock source via the wireless telephony communications module; receives, by the wireless communications module, a reference clock from the activated clock source; and synchronizing, by the wireless communications module, at least two internal devices thereof using the received reference clock. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows a schematic diagram of a communications system according to an embodiment of the invention; 
         FIG. 2  shows a schematic diagram of a mobile electronic device according to a first embodiment of the invention; 
         FIG. 3  shows corresponding waveforms of the clock requests, CapID values and the provided reference clock in an exemplary situation; 
         FIG. 4  shows corresponding waveforms of the clock requests, CapID values and the provided reference clock in another exemplary situation; 
         FIG. 5  shows a schematic diagram of a mobile electronic device according to a second embodiment of the invention; 
         FIG. 6  shows the hardware architecture of a Bluetooth module according to an embodiment of the invention; 
         FIG. 7  shows the hardware architecture of a WiFi module according to an embodiment of the invention; 
         FIG. 8  shows the hardware architecture of a GPS module according to an embodiment of the invention; 
         FIG. 9  shows a schematic diagram of a mobile electronic device according to an embodiment of the invention; 
         FIG. 10A  shows the flow chart of a method for controlling the VCXO by the MCU of the first wireless communications module  101  according to an embodiment of the invention; 
         FIG. 10B  shows an exemplary timeline for controlling the clock source when the VCXO is initially activated by an external wireless communications module; 
         FIG. 11  shows a schematic diagram of a mobile electronic device according to another embodiment of the invention; 
         FIG. 12A  shows the flow chart of a method for controlling the VCTCXO by the MCU of the first wireless communications module  101  according to an embodiment of the invention; 
         FIG. 12B  shows an exemplary timeline for controlling the clock source when the VCTCXO is initially activated by an external wireless communications module; 
         FIG. 13  shows a schematic diagram of a mobile electronic device  1300  according to another embodiment of the invention; 
         FIG. 14  is a schematic diagram illustrating HV3 packet transmissions at every six slots; 
         FIG. 15  is a diagram illustrating an exemplary connection state for the asynchronous connection oriented (ACL) link; 
         FIG. 16  is a diagram illustrating sniff anchor points; 
         FIG. 17  shows a schematic diagram illustrating EINT signal issuance; 
         FIG. 18  is a diagram showing exemplary interactions for delivering information indicating that a wireless local area network (WLAN) module will enter a Power Saving (PS) mode; 
         FIG. 19  is diagram showing exemplary interactions for obtaining buffered packets from an access point (AP); and 
         FIG. 20  shows a schematic diagram of frame exchange for obtaining buffered packets in a time line with an external interrupt (EINT) signal. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 1  shows a schematic diagram of a communications system according to an embodiment of the invention. A mobile electronic device  100  may be installed in a notebook, a cellular phone, a portable gaming device, a portable multimedia player, a Global Positioning System (GPS), a receiver, or others. The mobile electronic device  100  may comprise a plurality of wireless communications modules  101  to  103 , as shown in  FIG. 1 , to provide different wireless communications services. The wireless communications module  101  may communicate with a wireless communications device  201  in compliance with a specific protocol via the air interface. The wireless communications module  102  may communicate with a wireless communications device  202  in compliance with a specific protocol via the air interface. The wireless communications module  103  may communicate with a wireless communications device  203  in compliance with a specific protocol via the air interface. According to an embodiment of the invention, the wireless communications module  101  may be, for example, a GSM (Global System for Mobile Communications), WCDMA (Wideband Code Division Multiple Access), cdma2000, WiMAX (Worldwide Interoperability for Microwave Access), TD-SCDMA (Time Division Synchronous Code Division Multiple Access), LTE (Long Term Evolution), TD-LTE (Time Division Long Term Evolution) module, or the like, providing wireless telephony services, such as basic services, short message services (SMS), multimedia message services (MMS), supplementary services (SS), or others. The wireless communications module  102  or  103  may be a Bluetooth, ZigBee, WiBREE (Wireless BREE), WiFi, UWB (Ultra-WideBand), or GPS (Global Positioning System) module, or others. 
     According to an embodiment of the invention, the mobile electronic device  100  may further comprise a clock source  104 , shared between the wireless communications modules  101  to  103 , to provide a reference clock CLOCK. The frequency of the reference clock CLOCK may be, for example, 26 MHz, 15.36 MHz, 30.72 MHz, 32 MHz, or others. Note that those skilled in the art may also implement one or more than two wireless communications modules to connect to the wireless communications module  101  and share the clock source  104 , and the invention should not be limited thereto. Additionally, it is to be understood that the wireless communications modules may be integrated into an SoC (system on chip) and connect therebetween by internal wires, or different but similar bus architectures, or others. Several embodiments for controlling the clock source  104  shared between the wireless communications modules are proposed and discussed in the following paragraphs. 
       FIG. 2  shows a schematic diagram of a mobile electronic device  200  according to a first embodiment of the invention. In the first embodiment of the invention, the clock source  104  is controlled by one wireless communications module without coordinating with different wireless communications modules  101  to  103 . The clock source  104  may comprise at least an oscillation source  141  and a clock generator  142  to provide a clock signal as the reference clock CLOCK to different wireless communications modules for operations thereof. As previously discussed, the frequency of the reference clock CLOCK may be, for example, 26 MHz, 15.36 MHz, 30.72 MHz, 32 MHz, or others. The three wireless communications modules  101  to  103  may operate at different frequencies when they are in a busy mode (also called a wake-up mode). Any of the wireless communications modules may issue a request to activate the clock source  104  to provide the reference clock CLOCK thereto. According to an embodiment of the invention, the wireless communications module  101  may issue an internal clock request to activate the clock source  104  to provide the reference clock CLOCK when the wireless communications module  101  is going to enter or has entered a busy mode (also called a wake-up mode). According to another embodiment of the invention, the wireless communications module  101  may further receive the external requests CLK_Req from the wireless communications modules  102  and  103 , collect the external requests by an OR gate  115 , and output the collected result as the request CLK Req_Out to the clock source  104 . In the embodiments, the clock source  104  may be activated and the oscillation source  141  may start to oscillate in response to the request CLK_Req_Out. Note that the OR gate  115  may also be replaced with any other circuit or device performing substantially the same functions or achieving substantially the same results, and the invention should not be limited thereto. 
     As shown in  FIG. 2 , the wireless communications module  101  may comprise a micro controller unit (MCU)  111 , an interrupt request controller (IRQ controller)  113 , an IO register module  117  and an external memory interface (EMI) bus  119 . As one of ordinary skill in the art will readily appreciate, the basic functions of the MCU, IRQ controller, IO register and the EMI are already well-known in the art and are omitted here for brevity. It is also to be understood that the MCU and related portions of a digital circuit are powered down to save battery power when the reference clock is disabled (or inactivated). According to the embodiments of the invention, the clock source  104  may be a VCXO (voltage-controlled crystal oscillator), a VCTXO (voltage controlled temperature compensated crystal oscillator), a DCXO (digitally controlled crystal oscillator), or others. The oscillation source  141  may use the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency, and the clock generator  142  may accordingly provide a stable clock signal for digital integrated circuits of the wireless communications modules  101  to  103  for synchronization, and/or stabilize frequencies for radio transmitters and receivers installed in the wireless communications modules  101  to  103 . 
     According to the embodiment of the invention, the MCU  111  is capable of adjusting certain electrical characteristic of the clock source  104 , such as capacitance, voltage and the similar, via a control signal CLK Ctrl to reduce power consumption and maintain reference clock frequency with specific precision, or others. In the embodiments, the capacitance of the clock source  104  may be adjusted to several levels denoted as “CapID values”. As an example, a relatively smaller capacitance value indicates that a relatively smaller capacitance is provided so that the time required for the frequency of the reference clock to reach the target reference clock frequency would be relatively short. However, in the first embodiment of the invention, several drawbacks may occur, as shown in  FIG. 3  or  FIG. 4 , when the wireless communications module  101  controls the clock source  104  without considering the operating statuses of the other wireless communications modules  102  and  103 . 
       FIG. 3  shows corresponding waveforms of the clock requests, variations of CapID values and the provided reference clock in an exemplary situation. After receiving the external clock request CLK_Req from the wireless communications module  102  or  103 , the wireless communications module  101  may pass the clock request, via the OR gate  105  or a similar circuit, to activate the clock source  104  to provide the reference clock CLOCK to the wireless communications module  102  or  103 . During initiation, a relatively smaller capacitance (for example, CapID=0) of the clock source  104  may cause the output reference clock to reach a target frequency in a shorter time period than using a relatively larger capacitance. When the wireless communications module  101  wakes up and enters a busy mode, the clock source  101  may be started with the smallest amount of capacitance (for example, CapID=0), until reaching the target reference clock frequency (for example, 26 MHz). After that, the MCU  111  may adjust the capacitance to a calibrated level (for example, CapID=42) to yield a better performance (for example, +/−0.1 ppm clock drift). The mentioned adjustment to the capacitance of the clock source  101  may be referred to as a facilitating process to make the frequency of reference clock to achieve a target level. However, in an exemplary situation, as the clock source  104  has already been activated to provide clock to the wireless communications module  102  or  103  (e.g. a Bluetooth module), the capacitance adjustment triggered by the MCU  111  may dramatically change the output reference clock frequency to cause the operation of the second or the third wireless communications module to fail.  FIG. 4  shows corresponding waveforms of the clock requests, variations of CapID values and the provided reference clock in another exemplary situation. In this situation, the MCU  111  may maintain the capacitance of the clock source  104  with the calibrated level (for example, CapID=42) without any further adjustments to avoid the mentioned problems. However, maintaining the capacitance of the clock source  104  consumes more battery power and may increase the time required for the oscillator to reach the target reference clock frequency. Therefore, a second embodiment of the invention is provided to solve the mentioned problems. Note that the first embodiment as shown in  FIG. 2  and corresponding paragraphs are also a part of the invention developed during a design stage, and should not be regarded as the conventional technique. 
       FIG. 5  shows a schematic diagram of a mobile electronic device  500  according to the second embodiment of the invention. In the second embodiment of the invention, one wireless communications module controls the clock source  104  in a coordinated manner with consideration of the operating statuses of the other wireless communications modules. The fundamental hardware architecture and operation of the mobile electronic device  500  are similar to that of the mobile electronic device  200  shown in  FIG. 2 . Therefore, reference may be made to  FIG. 2  with the corresponding paragraphs and repeated descriptions are omitted here for brevity. As illustrated previously, the wireless communications module  101  may send out an internal clock request to activate the clock source  104  to provide a reference clock, such as a 26 MHz, 15.36 MHz, 30.72 MHz, 32 MHz clock, or others, when the wireless communications module  101  is going to enter or has entered a busy mode. In order to facilitate coordination between the three wireless communications modules  101  to  103 , the MCU  111  of the wireless communications module  101  may comprise one or more external interrupt (EINT) and/or general purpose input output (GPIO) connections to interface with the external wireless communications modules  102  and  103 . According to the second embodiment of the invention, when the wireless communications module  102  or  103  wakes up and enters a busy mode, the wireless communications module  102  or  103  may issue the external clock request CLK_Req to activate the clock source  104 , as well as, trigger an external interrupt (EINT) via an EINT interface or send a GPIO signal via a GPIO interface to notify the MCU  111  of the wireless communications module  101  that the clock source  104  has been requested for activating by another wireless communications module. The requests CLK_Req are collected by an OR gate  115  of the wireless communications module  101 . The clock source  104  may be activated and the oscillation source  141  may start to oscillate in response to the request CLK_Req_Out output by the OR gate  115 . Note that the OR gate  115  may be controlled and activated by the MCU  111  when the MCU  111  receives the EINT or GPIO signal. The OR gate  115  may also be replaced by any other circuit or device performing substantially the same functions or achieving substantially the same results, and the invention should not be limited thereto. Note also that the OR gate  115  may be alternatively implemented outside of the wireless communication modules, and the invention should not be limited thereto. 
     According to an embodiment of the invention, once detecting an EINT, the interrupt request (IRQ) controller  113  of the wireless communications module  101  may issue an IRQ to force the MCU  111  to load and execute an EINT handler containing a series of software codes. The executed EINT handler may adjust certain electrical characteristics of the main clock source  104 , such as capacitance, voltage and the similar, to reduce power consumption, maintain reference clock frequency, or others, at relevant times. According to another embodiment of the invention, when detecting a GPIO signal via the GPIO interface, a relevant bit of an IO register  117  is set to indicate an asynchronous event triggered by the wireless communications module  102  or  103 . The MCU  111  may periodically poll the bit of the IO register  117  to determine whether the clock source  104  has been activated by another outside wireless communications module. If so, a software routine is loaded and executed to adjust certain electrical characteristics of the clock source  104  at relevant times. The mentioned electrical characteristic adjustment of the clock source  104  may refer to a calibrated capacitance value “CapID” stored in an NVRAM (non-volatile random access memory)  106  of the mobile electronic device  500 . Note that according to an embodiment of the invention, the EINT handler or software routine may also be stored in the NVRAM  106 . Detailed description of the electrical characteristic adjustment of the clock source  104  will be illustrated in the following paragraphs. 
       FIG. 6  shows the hardware architecture of a Bluetooth module  600  according to an embodiment of the invention. Bluetooth is an open wireless protocol for exchanging data over short distances from fixed and mobile devices, creating personal area networks. Bluetooth systems occupy a section of the 2.4 GHz Industrial, Scientific, and Medical (ISM) band, which is 83 MHz-wide. The Bluetooth module  600  may operate as a master device controlling a personal area network (PAN) and/or operate as a slave device being wirelessly connected to the master device. The Bluetooth module  600  uses an inquiry scan procedure to discover nearby devices, or to be discovered by devices in their locality. The procedure for forming connections is asymmetrical and requires that one Bluetooth device carries out a page (connection) procedure while the other Bluetooth device is connectable (page scanning.) The procedure is targeted, so that the page procedure is only responded to by one specified Bluetooth device. The connectable device uses a special physical channel to listen for connection request packets from the paging (connecting) device. This physical channel has attributes that are specific to the connectable device, hence only a paging device with knowledge of the connectable device is able to communicate on the channel. Both paging and connectable devices may already be connected to other Bluetooth devices in a piconet. Two types of connections may be used for communications between a master device and a slave device. They are SCO/eSCO (synchronous connection oriented/extended synchronous connection oriented) links and ACL (asynchronous connection oriented) links. The execution of the above-mentioned and wireless data transceiving procedures are performed using a radio frequency (RF) module  604  and a Bluetooth MODEM  601 . The reference clock CLOCK output from the clock source  104  is fed to an internal clock generator and distributor  602  of the Bluetooth module  600 . The internal clock generator and distributor  601  may adjust the reference clock CLOCK to appropriate clock rates and drive the adjusted clock signals over a certain power level to the Bluetooth MODEM  601 , a VCO/PLL (voltage-controlled oscillator/phase lock loop)  605  in the circuit  604  and a system control logic  603  for operations thereof. For example, the VCO/PLL  605  may utilize an adjusted clock signal of 26 MHz to stabilize frequencies for radio transmitters and receivers. According to an embodiment of the invention, the internal clock generator and distributor  602  may be regarded as a PLL frequency synthesizer operating in a low frequency. The internal clock generator and distributor  602  may output stable 64 MHz and 32 MHz clock signals to the Bluetooth MODEM  601  and a system control logic  603 , respectively for synchronization therebetween. The adjustment to the reference clock CLOCK by the internal clock generator and distributor  601  may also refer to as converting CLOCK into one or more internal clocks and drives the internal clock(s) to the Bluetooth MODEM  601 , the circuit  604  and the system control logic  603  for synchronization therebetween. The system control logic  603  issues the external clock request CLK_Req, as well as, an EINT or a GPIO signal to the wireless communications module  101  when the Bluetooth module is going to enter or has entered a busy mode. In the busy mode, the Bluetooth MODEM  601  may transmit and/or receive a synchronous packet (such as a HV or DV packet) or an asynchronous packet (such as a DM, DH or AUX packet) via the RF module  604 . 
     For example, the SCO link (also called synchronization link) is a symmetric, point-to-point link between a master device and a specific slave device. The master and slave devices maintain the SCO link by using reserved slots at regular intervals. After establishing the SCO link, some synchronous packets (such as HV and DV packets) are typically used for voice transmissions and are not retransmitted. The master device sends synchronous packets at regular intervals depending on packet type used for transmission, for example, every 2, 4 or 6 slots for HV1, HV2 or HV3 packets, where each slot is typically 625 μs. HV and DV packets are typically transmitted via the SCO link. Exemplary HV3 packet transmissions at every six slots are depicted in  FIG. 14 . The ACL link (also called asynchronization link) is a point-multipoint (when link ID=0, broadcast) or point-to-point (when link ID not zero) link between the master device and all slave devices participating on a PAN (personal area network). No slot is reserved for the ACL link. The master device sends ACL packets on a per-slot basis to any slave device. After establishing the ACL link (i.e. entering connection state), ACL packets (such as DM, DH and AUX packets) are typically used for data transmissions. In addition, the master device regularly transmits packets to keep slave devices synchronized to the channel. 
     An exemplary connection state for the ACL link is illustrated in  FIG. 15 . During the active mode of a connection state  1510 , both master and slave devices actively participate on a channel. The master device schedules the transmission based on traffic demand to and from different slave devices. Additionally, during the sniff mode  1530 , the master device switches between transmitting and receiving packets to and from a slave device for sniff attempts containing 2, 4, 6, or 8 slots or more, after reaching sniff anchor points.  FIG. 16  illustrates sniff anchor points. The sniff anchor points are regularly spaced with an interval of T sniff . During an active mode of a connection state  1510 , the master device transmits data to a slave device via any one of the master-to-slave slots. During the sniff mode  1530 , a master device transmits data to a slave device in one or more of the master-to-slave slots for a sniff attempt after a sniff anchor point (e.g. a sniff attempt of T sniff  of  FIG. 16  after a sniff anchor point). It is to be understood that the active mode is entered (i.e. exits sniff mode) when a unsniff request is acknowledged while the sniff mode is entered when a sniff request is acknowledged. Before a sniff anchor point, the system control logic  603  issues an EINT or a GPIO signal to the wireless communications module  101  for activating the clock source  104 , as shown in  FIG. 17 . A guard time period between the ENT or GPIO signal issuance timing and the sniff anchor point is utilized to ensure that the reference clock CLOCK can be steadily provided before actual data transceiving. After the packet transceiving is completed, the system control logic  603  may notify the wireless communications module  101  to deactivate the clock source  104  and enters a low power mode. Thereafter, the wireless communications module  101  deactivates the clock source  104  if no wireless communication module utilizes that. 
       FIG. 7  shows the hardware architecture of a WiFi module  700  according to an embodiment of the invention. The WiFi module  700 , also called an IEEE 802.11 module, a wireless local area network (WLAN) module, or others, may be wirelessly used to connect to the Internet to browse web pages, transceive e-mails, chat on-line, download and play multimedia content, or others. The WLAN is typically implemented as an extension to wired LANs within a building and can provide the final few meters of connectivity between a wired network and mobile or fixed devices. Most WLAN systems may operate in the 2.4 GHz license-free frequency band and have throughput rates of up to 2 Mbps. The WiFi module  700  connects users via an access point (AP) to the LAN. The AP typically receives, buffers, and transmits data between the WiFi module  700  and the wired network infrastructure. Each AP may support, on average, twenty devices and have a coverage varying from 20 meters in areas with obstacles (walls, stairways, elevators) and up to 100 meters in areas with clear lines of sight. The access process of the WiFi module  700  may involve the following three steps: active/passive scanning, authentication and association performed via an RF module and a WiFi MODEM  701  thereof, enabling the WiFi module  700  to associate with an AP. Active scanning is used by the WiFi module  700  to scan surrounding wireless networks and locate a compatible one. Passive scanning is used by the WiFi module  700  to discover surrounding wireless networks by listening to beacon frames periodically sent by an AP. To prevent illegal access of a wireless network, authentication may be needed between the WiFi module  700  and an access controller (AC) managing all APs in a WiFi or between the WiFi and the associated AP. When the WiFi module  700  chooses a compatible network with a specified SSID and authenticates to an AP, it sends an association request frame to the AP. The AP sends an association response to the WiFi module  700  and adds the client&#39;s information to its database. An internal clock generator and distributor  702  of the WiFi module  700  receives the reference clock CLOCK generated by the clock source  104 . The internal clock generator and distributor  702  may adjust the reference clock CLOCK to appropriate clock rates and drive the adjusted clock signals over a certain power level to a WiFi MODEM  701 , a VCO/PLL  705  in the circuit (also referring to as RF module)  704  and a system control logic  703  for operations thereof. For example, the VCO/PLL  705  may utilize the adjusted clock signal of 26 MHz to stabilize frequencies for radio transmitters and receivers. According to an embodiment of the invention, the internal clock generator and distributor  702  may be regarded as a PLL frequency synthesizer operating in a low frequency. The internal clock generator and distributor  702  may output stable 40 MHz clock signals to both the WiFi MODEM  701  and a system control logic  703  for synchronization therebetween. The adjustment to the reference clock CLOCK by the internal clock generator and distributor  701  may also refer to as converting CLOCK into one or more internal clocks and drives the internal clock(s) to the WiFi MODEM  701 , the circuit  704  and the system control logic  703  for synchronization therebetween. The system control logic  703  issues an external clock request CLK_Req, as well as, an EINT or a GPIO signal to the wireless communications module  101  when the WiFi module  700  is going to enter or has entered a busy mode. 
     In order to extend the battery life, the WLAN module goes into a power saving (PS) mode (also called sleep mode) for long time periods. Information indicating that PS mode will be entered in after the transmission of this frame is further notified to its associated access point (AP), as shown in  FIG. 18 . Subsequently, the AP maintains a continually updated record of the WLAN module currently working in the PS mode, and buffers the packets addressed to the WLAN module until the WLAN module specifically requests the packets by sending a polling request (briefly in PS-Poll). In the busy mode, the WiFi MODEM  601  may listen to a Beacon Frame from the AP and receive buffered data if required via the RF module  604 . As part of a Beacon Frame, the AP periodically transmits information regarding which WLAN modules have packets buffered at the AP, where the information is carried in a traffic indication map (TIM) Information Element of the frame body field of the MAC data. Thus, the WLAN module periodically enters the busy mode (wakes up) to receive the Beacon Frame. Before receiving the Beacon Frame via the WiFi MODEM  701  and the RF module, the system control logic  703  issues an EINT or a GPIO signal to the wireless communications module  101  for activating the clock source  104 . A guard time period between the ENT or GPIO signal issuance timing and the Beacon Frame receiving is utilized to ensure that the reference clock CLOCK can be steadily provided before actual data receiving. If there is an indication indicating at least one packet stored at the AP and waiting for delivery, then the WLAN module stay the busy mode and sends a PS-Poll to the AP to obtain the buffered packet. Otherwise, the system control logic  703  may notify the wireless communications module  101  to deactivate the clock source  104  and enter the sleep mode. Thereafter, the wireless communications module  101  deactivates the clock source  104  if no wireless communication module utilizes that. The signaling between the WLAN module and the AP for acquisition of buffered packets may refer to  FIG. 19 .  FIG. 20  shows a schematic diagram of frame exchange for obtaining buffered packets in a time line with EINT signal. After receiving a PS-Poll  1910 , the AP replies with an acknowledgment  1920  and subsequently transmits a buffered frame  1930 . Once successfully receives the buffered data, the WLAN module replies with an acknowledgement  1940 , and examines a more data bit of the prior received frame to determine whether more buffered packet is required to be received. If so, the WLAN module stays the busy mode and repeatedly sends PS-Poll to the AP to obtain more buffered packets. 
       FIG. 8  shows the hardware architecture of a GPS module  800  according to an embodiment of the invention. The GPS module  800  is capable of determining the latitude and longitude of a receiver on earth by calculating the time difference for GPS radio signals from different GPS satellites to reach the receiver. Specifically, the GPS module  800  calculates its position by measuring the distance between itself and three or more GPS satellites. Measuring the time delay between transmission and reception of each GPS radio signal gives the distance to each satellite, since the signal travels at a known speed. The signals also carry information about the satellites&#39; location. Typically, by determining the position of, and distance to, at least three satellites, the GPS module  800  can compute its position using trilateration. An internal clock generator and distributor  802  of the GPS module  800  receive the reference clock generated by the main clock source  104 . The internal clock generator and distributor  802  may adjust the reference clock CLOCK to appropriate clock rates and drive the adjusted clock signals over a specific power level to a GPS demodulator  801 , a VCO/PLL  805  in the circuit  804  and a system control logic  803  for operations thereof. For example, the VCO/PLL  805  in the circuit  804  may utilize the adjusted clock signal of 26 MHz to stabilize frequencies for radio receivers. According to an embodiment of the invention, the internal clock generator and distributor  802  may be regarded as a PLL frequency synthesizer operating in a low frequency. The internal clock generator and distributor  802  may output stable 130 MHz and 78.4 MHz clock signals to the GPS demodulator  801  and a system control logic  803 , respectively for synchronization therebetween. The system control logic  803  issues an external clock request CLK_Req, as well as, an EINT or a GPIO signal to the wireless communications module  101  when the GPS module  800  is going to enter or enters a busy mode. 
     As described previously, the clock source  104  may be a VCXO, a VCTXO, a DCXO, or others. In the following paragraphs, some embodiments for controlling a VCXO, a VCTXO and a DCXO will be introduced.  FIG. 9  shows a schematic diagram of a mobile electronic device  900  according to an embodiment of the invention. In the embodiment of the invention, the clock source  904  may be implemented in a VCXO containing at least a crystal oscillator  941 , a capacitance providing unit  942  and a clock provider  943  with a VCO/PLL  944 , as shown in the lower-left part of  FIG. 9 . The frequency of the VCXO may be varied by only typically a few tens of parts per million (ppm), because the high Q factor of the crystal oscillator allows pulling over only a small range of frequencies. The capacitance providing unit  942  of the VCXO can be adjusted by the executed EINT handler or software routine of the wireless communications module  101  to provide a specific amount of capacitance. The capacitance providing unit  942  may contain multiple capacitors each controlled by a voltage, and the voltage may be adjusted according to the received CapID value carried in the control signal CLK_Ctrl to provide a specific amount of capacitance. Alternatively, the capacitance providing unit  942  may contain multiple capacitors with switching devices, and the switching devices may be controlled according to the received CapID value carried in the control signal CLK_Ctrl to provide a specific amount of capacitance. Related references for controlling the capacitance providing unit  942  can be made to description of  FIG. 2 . The EINT handler or software routine may further contain an automatic frequency control (AFC) logic to adjust voltage (e.g. +/−0.1 ppm) to the VCO/PLL  944  of the VCXO  904  based on broadcasted signals from a base station, such as the wireless communications device  201 , ensuring that precision of the frequency of the output reference clock CLOCK can be limited to a small range. In an AFC procedure, the clock rate or phase error between the clocks of the base station and the wireless communications module  101  are detected by the AFC logic. Thereafter, the voltage to the VCO/PLL  944  is adjusted accordingly so as to compensate for any frequency drift. Those skilled in the art may alternatively arrange the AFC logic outside of the EINT handler or software routine and embed it in another periodic activated subroutine. It is to be understood that the adjustment command to the VCO/PLL  944  may also be converted into a relevant voltage by a digital-to-analog converter (DAC)  116 . 
       FIG. 10A  shows the flow chart of a method for controlling the VCXO by the MCU  111  of the wireless communications module  101  according to an embodiment of the invention. After detecting a request to activate the clock source  904  from any external wireless communications module  102  or  103  via the EINT or GPIO interface (Step S 1001 ), the MCU  111  of the wireless communications module  101  determines whether the reference clock has been stably generated or provided by the clock source  904  (Step S 1002 ). When the reference clock has not been stably generated or provided by the clock source  904 , meaning that the clock source has been initially activated by the external wireless communications module  102  or  103  to provide the reference clock, the MCU  111  loads and executes a corresponding EINT handler or software routine, or others, which is stored in the NVRAM (Step S 1003 ). Next, the MCU  111  adjusts an electrical characteristic of the clock source  904  through the executed EINT handler or software routine by setting the CapID value to shorten the clock settling time (Step  1004 ). As an example, the MCU  111  of wireless communications module  101  may adjust the electrical characteristic of the clock source  904  by first adjusting a capacitance of the clock source  904  to a relatively smaller level to shorten the clock settling time for a time interval, and then increasing the capacitance of the clock source  904  to a target level to provide a stable reverence clock. It is to be understood that the CapID value may be carried in the control signals CLK_Ctrl or converted into a control voltage by the DAC to adjust the capacitance of the VCXO to a relevant level. When the reference clock has been stably generated or provided, meaning that the clock source has already provided a stable reference clock to any other wireless communications module (i.e. any wireless communications module other than the one that is making the request), the capacitance of the VCXO will not be changed and an AFC procedure may continue to maintain the reference clock with a specific precision until all of the wireless communications modules leave the busy modes (Step S 1005 ). It is to be understood that the reference clock has been stably generated when it is output with the designated frequency varied within a small range. In the AFC procedure, the voltage of the VCXO is periodically adjusted based on broadcasted signals from a base station, ensuring that a frequency precision of the output reference clock can be limited to a small range. Next, the executed EINT handler or software routine continuously monitors the statuses of all wireless communications modules (Step S 1006 ), and checks whether all wireless communications modules are not in busy modes (Step S 1007 ). When all wireless communications modules are not in busy modes, the clock source  904  may be deactivated to save battery power (Step S 1008 ). Otherwise, the process may loop back to step S 1005  to re-execute the AFC procedure. 
       FIG. 10B  shows an exemplary timeline for controlling the clock source  904  when the VCXO is initially activated by an external wireless communications module. The time period T 1  is called a clock settling time period for loading and executing the EINT handler or software routine, or other preparatory tasks. During the time period T 2 , the executed ENT handler or software routine controls capacitors of the VCXO. After the second time period T 2 , the reference clock has been stably generated and the AFC procedure may be repeatedly executed to maintain the output reference clock with a specific precision. 
       FIG. 11  shows a schematic diagram of a mobile electronic device  1100  according to another embodiment of the invention. In the embodiment of the invention, the clock source  1104  may contain at least a VCTCXO  1141  and a clock provider  1142 , as shown in the lower-left part of  FIG. 11 . Other than the VCXO, the capacitance of VCTCXO  1141  is automatically adjusted and should not be changed by the wireless communications module  101 . Similarly, the voltage to the VCTCXO may be adjusted (e.g. +/−0.1 ppm) by an executed EINT handler or software routine based on broadcasted signals from a base station, ensuring that a frequency precision of the output reference clock can be limited to a small range. It is to be understood that the adjustment command to the VCTCXO  1141  may be converted into a relevant voltage by a DAC  116 . 
       FIG. 12A  shows the flow chart of a method for controlling the VCTCXO by the MCU  111  of the wireless communications module  101  according to an embodiment of the invention. After detecting a request to activate the clock source  1104  from any external wireless communications module  102  or  103  via the EINT or GPIO interface (Step S 1201 ), the MCU  111  of the wireless communications module  101  determines whether the reference clock has been stably generated or provided by the clock source (Step S 1202 ). When the reference clock has not been stably generated or provided by the clock source  1104 , meaning that the clock source  1104  has been initially activated by the external wireless communications module  102  or  103  to provide the reference clock, the MCU  111  loads and executes a corresponding EINT handler or software routine, or others, which is stored in the NVRAM (Step S 1203 ). When the reference clock has been stably generated or provided, meaning that the clock source  1104  has already provided a stable reference clock to any other wireless communications module (i.e. any wireless communications module other than the one that is making the request), an AFC procedure may continue to maintain the reference clock with a specific precision until all of the wireless communications modules leave the busy modes (Step S 1204 ). It is to be understood that the reference clock has been stably generated when it is output with a designated frequency varied within a small range. In the AFC procedure, the voltage of the VCTCXO may be periodically adjusted based on broadcasted signals from a base station, ensuring that frequency precision of the output reference clock can be limited to a small range. Next, the executed EINT handler or software routine continuously monitors the statuses of all wireless communications modules (Step S 1205 ), and checks whether all wireless communications modules are not in busy modes (Step S 1206 ). When all wireless communications modules are not in busy modes, the clock source  1104  may be deactivated to save battery power (Step S 1207 ). Otherwise, the process may loop back to step S 1204  to re-execute the AFC procedure. 
       FIG. 12B  shows an exemplary timeline for controlling the clock source  1104  when the VCTCXO is initially activated by an external wireless communications module  102  or  103 . The time period T 3  is the clock settling time period for loading and executing the EINT handler or software routine, or other preparatory tasks. After the time period T 3 , the AFC procedure may be repeatedly executed to maintain the output reference clock with a specific precision. 
       FIG. 13  shows a schematic diagram of a mobile electronic device  1300  according to another embodiment of the invention. In the embodiment of the invention, the clock source  1304  may be implemented in a DCXO comprising a crystal oscillator  1341 , a capacitance providing unit  1342 , a clock provider  1343 , a VCO/PLL  1344 , and further comprising a digital interface and a DAC  1345  as shown in the lower-left part of  FIG. 13 . The digital interface receives digital commands from the MCU  111 , and feeds them to the DAC  1345  to be converted into voltage for an AFC logic. The flow chart of the method for controlling the DCXO by the MCU  111  may be found in  FIG. 10A , and the exemplary timeline when the DCXO is initially activated by an external wireless communications module may be found in  FIG. 10B . 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. Therefore, the scope of the present invention shall be defined and protected by the following claims and their equivalents.