Patent Publication Number: US-7210619-B2

Title: Systems and methods for power reduction in systems having removable media devices

Description:
PRIORITY 
   This application is a continuation of U.S. patent application Ser. No. 10/762,684 titled “Systems and Methods for Power Reduction in Systems Having Removable Media Devices” filed Jan. 20, 2004 now U.S. Pat. No. 7,086,583, whose inventor is Henry Wurzburg. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to the field of computer systems and, more particularly, to peripheral devices. 
   2. Description of the Related Art 
   The Universal Serial Bus (USB) allows coupling of peripheral devices to a computer system. USB is a serial cable bus for data exchange between a host computer and a wide range of simultaneously accessible devices. The bus allows peripherals to be attached, configured, used, and detached while the host is in operation. For example, a card reader for reading flash memory cards may be coupled to a host computer through the USB. USB based systems may require that a USB host controller be present in the host system, and that the operating system (OS) of the host system support USB and USB Mass Storage Class Devices. A USB hub may be coupled to a USB host controller to allow multiple USB devices to be coupled to the host system through the USB host controller. In addition, other USB hubs may be coupled to the USB hub to provide additional USB device connections to the USB host controller. 
   In recent years the electronics marketplace has seen a proliferation of appliances and personal electronics devices that use solid-state memory. For example, traditional film cameras have been losing market share to digital cameras capable of recording images that may be directly downloaded to and stored on personal computers (PCs). The pictures recorded by digital cameras can easily be converted to common graphics file formats such as Joint Photographic Experts Group (JPEG), Graphic Interchange Format (GIF) or Bitmap (BMP), and sent as e-mail attachments or posted on web pages and online photo albums. Many digital cameras are also capable of capturing short video clips in standard digital video formats, for example Moving Picture Experts Group (MPEG), which may also be directly downloaded and stored on personal computers (PCs) or notebook computers. Other devices that typically use solid-state memory include personal digital assistants (PDAs), pocket PCs, video game consoles and Moving Picture Experts Group Layer-3 Audio (MP3) players. 
   The most widely used solid-state memory devices include flash-memory chips configured on a small removable memory card, and are commonly referred to as flash-memory cards. The majority of flash-memory cards currently on the market are typically one of: Compact Flash™, MultiMediaMemory™ memory card (MMC) and the related Secure Digital Memory card (SD), SmartMedia™ memory card (SM), xD Picture CardS™ (xD), and Memory Stick™. Most digital cameras, for example, use Compact Flash™ memory cards to record images. Many PDA models use Memory Stick™ memory cards to hold data. Some MP3 players store music files on SM memory cards. Generally, data saved by PDAs and other handheld devices using flash-memory cards are also transferred or downloaded to a PC. In the present application, the term “flash-memory” is intended to have the full breadth of its ordinary meaning, which generally encompasses various types of non-volatile solid-state memory devices as described above. 
   Typically, a flash-memory card can easily be removed from the utilizing device. For example, a Compact Flash™ memory card can be removed from a digital camera much like film is removed from a standard camera. The flash-memory card can then be inserted into an appropriate flash-memory card reader coupled to a PC, and the image files directly copied to the PC. It should be noted that while a majority of smaller hand-held computers and PDAs have slots that receive Compact Flash™ memory cards, currently, most PCs do not, hence the need for a flash-memory card reader connecting to the PC. Most recently the preferred interface between flash-memory card readers and PCs has been the Universal Serial Bus, where the flash-memory card reader is connected to a USB port on the PC via a USB cable. Portable computer or notebook PCs typically also have PC-memory card (earlier known as Personal Computer Memory card International Association; PCMCIA) slots that, can receive PCMCIA memory cards configured as flash-memory card readers. 
   In all, the many different memory card formats present a wide array of interface requirements not only for PCs but for other digital systems as well, such as embedded systems. Different adapters are needed for each of the memory card formats. One solution to consolidate the interfacing of flash-memory cards to desktop and portable computer PCs has been the design and manufacture of multi-format flash-memory card readers that are capable of reading the most popular formats. Such memory card-readers are sometimes referred to as ‘Seven-in-one’ readers indicating that they may be used with the currently popular flash-memory card formats. As indicated above, such multi-format card readers are typically designed with a USB interface. 
   While USB devices, such as multi-format card readers and USB hubs designed with a USB interface, are typically connected to host PCs and/or notebook PCs via a USB cable, they may also be designed into computers as embedded USB devices. Typically, adding an embedded USB device, such as a card reader or hub, to a computer adversely affects power consumption of the computer. In general, a USB device attached to the USB host controller of the computer may prevent the central processing unit (CPU) of the computer from entering a low power state—e.g., the C3 state. The USB host controller, as a bus mastering peripheral, may keep the PCI bus active as long as it is attached to a USB device preventing the CPU from going into a low power state. This may especially be a problem for embedded devices (e.g., an embedded card reader). Unnecessary power may also be used to power a memory card that is not in use. When a memory card or multiple memory cards are inserted in a memory card-reader, they are normally fully powered as long as the memory card-reader is not in SUSPEND mode. In such case, the memory card can typically dissipate up to 100 mA, adversely affecting battery life. 
   SUMMARY OF THE INVENTION 
   In various embodiments, a USB device (e.g., a USB hub or card reader) coupled to a USB host controller may communicate with the USB host controller through an upstream port. In some embodiments, a USB hub may be coupled to a USB port to provide additional USB ports. Data may be transmitted from the USB device to the USB host controller and then used by a central processing unit (CPU). In some embodiments, if the USB device is turned off or is not in an active state (e.g., no cards are present in a USB card reader or no devices are attached to a USB hub), an algorithm (e.g., from the device&#39;s firmware) may be implemented to electrically disconnect the USB device from the USB host controller. In some embodiments, when the USB device is electrically disconnected from the USB host controller and no system activity from a bus mastering peripheral is occurring on the PCI bus, the CPU may enter a low power state (other system conditions may also need to be met). 
   In various embodiments, a USB device, such as a card reader, may be embedded in a portable computer, such as a laptop. The card reader may read data from memory cards inserted into the card reader. If no memory cards are inserted in the card reader, an algorithm in the card reader&#39;s firmware may be implemented to electrically disconnect the card reader from a USB host controller. In some embodiments, when the card reader is electrically disconnected from the USB host controller and no system activity from a bus mastering peripheral is occurring on the PCI bus, the CPU may be allowed to enter a low power state (other conditions may also need to be met). In some embodiments, the card reader may be electrically disconnected or electrically reconnected from the USB host controller by a sideband signal from the computer to signal the card reader when to electrically disconnect and electrically reconnect. 
   In some embodiments, if a card is inserted into the card reader, but has not been accessed for a first specified amount of time (e.g., 10 seconds), the card reader may power down the card. If the card is then accessed, the card reader may restore power to the card. In some embodiments, an algorithm in the card reader&#39;s firmware may power the card up and down. In some embodiments, a sideband signal may be sent to the card reader to signal the card reader to electrically disconnect after the card has been powered down. In some embodiments, the card may be powered down approximately at the same time that the card reader is electrically disconnected. In some embodiments, a sideband signal may be used to signal the card reader when to electrically reconnect. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing, as well as other objects, features, and advantages of this invention may be more completely understood by reference to the following detailed description when read together with the accompanying drawings in which: 
       FIG. 1  illustrates a portable computer for various embodiments; 
       FIG. 2  is a block diagram of one embodiment of a computer, according to an embodiment; 
       FIG. 3  illustrates a diagram of a card reader coupled to a USB host controller, according to an embodiment; 
       FIG. 4  illustrates a diagram of a USB device coupled to a USB host controller, according to an embodiment; 
       FIG. 5  illustrates a diagram of a hub with an attach detect logic and a physical interface, according to an embodiment; 
       FIG. 6  illustrates a flowchart of a method for electrically disconnecting and electrically reconnecting a device from to a USB host controller, according to an embodiment; 
       FIG. 7  illustrates a flowchart of a method for electrically disconnecting and electrically reconnecting a card reader to a USB host controller, according to an embodiment; 
       FIG. 8  illustrates a flowchart of a method for electrically disconnecting and electrically reconnecting a hub to a USB host controller, according to an embodiment; 
       FIG. 9  illustrates a flowchart of a method for regulating the CPU, according to an embodiment; and 
       FIG. 10  illustrates a flowchart of a method for regulating a CPU while attached to a hub, according to an embodiment. 
   

   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Note, the headings are for organizational purposes only and are not meant to be used to limit or interpret the description or claims. Furthermore, note that the word “may” is used throughout this application in a permissive sense (i.e., having the potential to, being able to), not a mandatory sense (i.e., must).” The term “include”, and derivations thereof, mean “including, but not limited to”. The term “coupled” means “directly or indirectly connected”. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates an embodiment of a portable computer  101  for various embodiments. Embodiments of the invention may be used with various different types of systems of computers, and portable computer  101  is one exemplary embodiment. 
   In some embodiments, the portable computer  101  may be used with multiple peripheral devices such as, but not limited to, Universal Serial Bus (USB) devices (e.g., computer mouse  111 , scanners, printers, external memory devices, cameras, personal digital assistants (PDAs), keyboards, touchscreens, and joysticks). Other peripheral devices are also contemplated. 
     FIG. 2  is a block diagram of one embodiment of computer  101 . In some embodiments, north bridge  205  (an integrated chip) couples the central processing unit (CPU)  203  and the system memory  201  to the peripheral component interconnect (PCI) bus  207  (used to connect peripherals to the computer). As shown, south bridge  209  couples to the PCI bus  207 . In some embodiments, south bridge  209  may include a USB host controller  211  to communicate through a USB port  213  with a USB device  215 . The USB port  213  and USB device  215  may be internal or external to the computer. In some embodiments, the USB host controller  211  may provide a peripheral bus interface between the USB device  215  and the computer. 
   Referring again to  FIG. 1 , in some embodiments, USB devices, such as a card reader  113 , may communicate with a computer (e.g., portable computer  101 ) through a USB host controller  211  in a PC chipset. The USB host controller  211  may regulate communication with attached USB devices (e.g., scheduling bandwidth on the bus). Communication speeds with the USB devices coupled to the USB host controller  211  may include low speed (LS), full speed (FS), and high speed (HS). In some embodiments, USB devices may be coupled to a computer (e.g., portable computer  101 ) through one or more USB ports  103 . The USB ports  103  may be on the portable computer  101  or on a docking station (not shown) coupled to the portable computer  101 . A USB connector  109  may plug into a USB port  103  to couple a USB device to the portable computer  101 . 
   In some embodiments, a hub (not shown) may be coupled to a USB port  103  of the portable computer  101  to provide additional USB ports. An internal hub may be used to provide multiple. USB ports. For example, an internal hub may provide USB ports  103   a,    103   b,  and  103   c.  In some embodiments, the hub may be internal to the portable computer  101 , while, in some embodiments, the internal hub may be in a docking station for the portable computer  101 . Other external hubs may be coupled to one of the USB ports  103  to provide additional USB ports for use. Multiple hubs may be chained together to provide even more USB ports. 
   In some embodiments, the USB host controller  211  may detect USB devices as they are connected to a USB port  103 , interrogate the USB device (e.g., to find out what speed to use for communication with the device and device capabilities), and load a driver to support the USB device. USB devices may communicate with the USB host controller  211  using control, interrupt, bulk, and isochronous transfers. In addition, the USB device may be powered over the USB bus, while some USB devices may be self powered. When a USB device is unplugged from a USB port  103 , the USB host controller may detect the absence of the USB device and unload the driver. In some embodiments, a USB hub may not electrically connect to the USB host controller  211  until a device is coupled to the USB hub. In addition, some card readers  113  may not electrically connect to the USB host controller  211  until a card is inserted into the card reader  113 . 
     FIG. 3  illustrates an embodiment of a card reader  301  coupled to a USB host controller  211 . In some embodiments, a card reader  301  may be embedded in a computer, such as a portable computer  101 . The card reader  301  may communicate with a USB host controller  211  through an upstream port  305 . The card reader  301  may use a controller  325  and a physical interface  303  to assist in reading, writing, and transferring data. The memory card  309  may be inserted into the card reader  301  through memory card slot  307 . While the card reader  301  is shown with one card slot  307 , a card reader  301  with multiple card slots may also be used. In some embodiments, the memory card may be a SmartMedia™ (SM) memory card, xD Picture Cards™ (xD), a Memory Stick™, a High Speed Memory Stick (HSMS), a Memory Stick PRO™ (MSPRO), a Secure Digital (SD) memory card, a MultiMediaMemory™ memory card (MMC), NAND Flash, Compact Flash™ (CF) or a CF form-factor Advanced Technology Attachment (ATA) hard drive. Other memory cards are also contemplated. In various embodiments, a cable between an upstream port  305  and a device (not shown) may carry a power line  321 , ground  324 , and a pair of data lines  322 ,  323  (D+ and D−) to transfer data between the card reader  301  and the computer. For full speed card readers, when the card reader  301  is attached to a USB port, the card reader  301  may pull the D+ line  322  high to approximately 3.3 volts using a pull up resistor (not shown) on the D+ line  322 . The USB host controller may then detect the presence of the card reader  301  on the bus and reset the card reader  301 . High speed devices connect the same way as full speed devices except, during reset, the device, such as a high speed card reader, “chirps” by driving the D− line  323  high. The USB host controller responds by alternately driving the D+ and D− lines high. When the high speed device detects the alternating chirps, the high speed device electrically removes the pull up resistor to balance the line and continues communicating at high speed. In some embodiments, the D+ and D− lines ( 322 , 323 ) may interact with the physical interface  303  through an attachment indicator mechanism  302 . 
   In some embodiments, if no memory card  309  is inserted in the card reader  301  (i.e., the card reader  301  is not in an active state) or the card reader  301  is turned off, an algorithm (e.g., stored in firmware on the card reader  301 ) may be implemented in the card reader  301  to electrically disconnect the card reader  301  from the USB host controller  211 . Firmware may be on a read only memory (ROM) or a programmable read only memory (PROM) accessible by the card reader (e.g., internal or external memory). For example, firmware may be on an Electrically Erasable Programmable Read-Only Memory (EEPROM) that may be externally attached/detached to the card reader to activate/deactivate the electrical disconnect feature. For full speed devices to electrically disconnect, the pull up resistor may be electrically removed (i.e., set to a high impedance or “tri-stated”) from the D+ line. The USB host controller may interpret this as a disconnect. To electrically disconnect high speed devices, the D+ and D− lines may both be tri-stated (set to a high impedance). 
   In some embodiments, when the card reader  301  is electrically disconnected from the USB host controller  211  and no system activity from a bus mastering peripheral is occurring on the PCI bus  207 , the CPU  203  may enter a low power state. In some embodiments, if a memory card  309  is in the memory card slot  307 , but has not been accessed in a first specified amount of time (e.g., 10 seconds), the memory card  309  may be powered down. In some embodiments, if a sideband signal is available, a sideband signal may be sent to signal the card reader  301  when to electrically disconnect and electrically reconnect. In one embodiment, if the card has not been accessed for a second specified amount of time (e.g., 10 minutes), the card reader  301  may be sent a sideband signal to electrically disconnect from the USB host controller  211 . In some embodiments, the card reader  301  may not electrically disconnect from the USB host controller  211  with a memory card  309  inserted unless a sideband signal can be sent to the card reader  301  to signal it to electrically connect when needed. While an embodiment of a card reader  301  is shown in  FIG. 3 , it is to be understood that other embodiments may include other devices with removable medium. In addition, other devices coupled to the USB host controller  211  may also be electrically disconnected as seen in  FIG. 4 . 
     FIG. 4  illustrates an embodiment of a USB device  401  coupled to a USB host controller  211 . In some embodiments, a USB device  401  may be embedded in a computer, such as a portable computer  101 . The USB device  401  may communicate with a USB host controller  211  through an upstream port  305 . In some embodiments, the USB device  401  may have a controller  325  and a physical interface  303 . Data may be transmitted from the USB device  401  to the USB host controller  211  and then used by a CPU  203 . In some embodiments, if the USB device  401  is turned off or if the device  401  is not in an active state, an algorithm may be implemented to electrically disconnect the USB device  401  from the USB host controller  211 . However, in some embodiments, the USB device  401  may not be electrically disconnected unless the USB device  401  has a way of being signaled to electrically reconnect to the USB host controller (e.g., by inserting a card into a card reader or attaching a device to a USB hub). In some embodiments, if a sideband signal can be used to signal the USB device  401  when to electrically disconnect and when to electrically reconnect, the USB device  401  may be signaled to electrically disconnect if the USB device  401  has not been used in a second specified amount of time (e.g., 10 minutes). A sideband signal may then be used to signal the USB device  401  to electrically reconnect. 
   In some embodiments, when the USB device  401  is electrically disconnected from the USB host controller  211  and no system activity from a bus mastering peripheral is occurring on the PCI bus  207 , the CPU  203  may enter a low power state. In some embodiments, a USB device  401  may be electrically disconnected through a physical interface on the USB device  401 . For example, as described above, the physical interface  303  may tri-state (i.e., set to a high impedance) the D+ or the D+ and D− lines (i.e., the FS and HS transceivers) on the USB device  401  and remove any termination from the universal serial bus. 
     FIG. 5  illustrates a diagram of an embodiment of a hub  501  with an attach detect logic  511  and a physical interface  303 . In some embodiments, a hub  501  may be used to provide multiple downstream ports  513  for USB devices. For example, if hub  501  is internal to the portable computer  101 , downstream ports  513  may be provided through USB ports  103  (see  FIG. 1 ). The hub  501  may communicate through an upstream port  305  using a physical interface  303 . In some embodiments, the upstream port  305  may be an external USB port (e.g., USB port  103 ), or, if the hub is internal to the portable computer  101 , may be an internal connection to a USB host controller  211 . In various embodiments, an attach detect logic  511  may be provided within the hub  501  to detect if a device is coupled to downstream ports  513 . An auto detach logic  507  may be activated by a configuration bit loaded from an EEPROM  509 . In some embodiments, the auto detach logic  507  may be activated by firmware internal to the hub  501 . In some embodiments, if the attach detect logic  511  does not detect a device coupled to the downstream ports  513 , a no ports signal  517  may be sent to the auto detach logic  507 . The auto detach logic  507  may send a detach signal  515  to the physical interface  303  if the auto detach logic  507  has been configured by a configuration bit  519  from the EEPROM  509  and receives the no ports signal  517  from the attach detect logic  511 . In some embodiments, if a device is not coupled to the hub  501 , the hub  501  may be electrically disconnected after a wait period. If a device is coupled to the hub  501  during the wait period, the hub may not be electrically disconnected. 
   In some embodiments, a sideband signal may be used to signal the hub  501  when to electrically disconnect and when to electrically reconnect. The hub  501  may be signaled by a sideband signal from the computer  101  to electrically disconnect if the hub  501  has not been used in a second specified amount of time (e.g., 10 minutes). A sideband signal may then be used to signal the hub  501  to electrically reconnect at a later time. In some embodiments, a sideband signal may be sent to the hub  501  when the computer goes into a SUSPEND mode to signal the hub  501  into a reduced functionality mode in which the hub  501  may only respond to a device trying to activate/wake the computer from SUSPEND mode (e.g., movement from a mouse coupled to the hub  501 ). The reduced functionality mode, and other modes signaled by the sideband signal, may result in lower power usage from the hub  501 . 
     FIG. 6  illustrates a flowchart of an embodiment of a method for electrically disconnecting a device from a USB host controller. It should be noted that in various embodiments of the methods described below, one or more of the steps described may be performed concurrently, in a different order than shown, or may be omitted entirely. Other additional steps may also be performed as desired. 
   At  601 , a determination is made whether a device is coupled to the USB host controller and in an active state. For example, a card in a card reader or a device attached to a USB hub may indicate the card reader and USB hub are in active states. 
   At  603 , if a device is not in an active state, the device may be electrically disconnected from the USB host controller. In some embodiments, if the device is not in an active state, the device may be electrically disconnected after a wait period in case the device becomes active again relatively quickly. If the device becomes active during the wait period (e.g., 2–3 seconds), the device may not be electrically disconnected. Other wait periods are also contemplated (e.g., 1–2 minutes, 10–20 minutes, etc.). In some embodiments, firmware may comprise algorithms to electrically disconnect the device if the device is not in an active state. However, in some embodiments, the USB device may not be electrically disconnected unless the USB device has a way of being signaled to electrically reconnect to the USB host controller (e.g., by a user inserting a card into a card reader, or receiving a sideband signal from the computer). 
   At  605 , if a device is in an active state, an electrical connection between the device and the USB host controller may be maintained. 
   At  607 , if the device enters an active state after the device is electrically disconnected, at  609 , the device may be electrically reconnected to the host controller and flow may resume at  601 . If the device is not in an active state, at  611 , the device may be maintained in an electrically disconnected state and the flow may continue at  607 . 
     FIG. 7  illustrates a flowchart of an embodiment of a method for electrically disconnecting a card reader from a USB host controller. It should be noted that in various embodiments of the methods described below, one or more of the steps described may be performed concurrently, in a different order than shown, or may be omitted entirely. Other additional steps may also be performed as desired. 
   At  701 , a determination may be made whether a memory card is in the memory card slot of a card reader coupled to the USB host controller. In other embodiments, a determination may be made as to whether a removable storage medium is in a removable storage medium&#39;s reading device. 
   At  703 , if there is no memory card in the memory card slot, at  705 , the card reader may be electrically disconnected from the USB host controller. In some embodiments, if the there is no memory card in the card reader, the card reader may be electrically disconnected after a wait period in case the user is switching out cards, etc. If a card is inserted during the wait period (e.g., 2–3 seconds), the card reader may not be electrically disconnected. Other wait periods are also contemplated. In some embodiments, to electrically disconnect the card reader, a physical interface for the card reader may tri-state both FS and HS transmitters on the card reader and remove any termination from the universal serial bus. For example, the D+ line (full speed devices) or the D+ line and the D− line (high speed devices) may be set to a high impedance. 
   At  707 , if there is a memory card in the memory card slot, a determination may be made whether the memory card has been accessed in a first specified amount of time. In some embodiments, the first specified amount of time may be approximately 10 seconds. Other first specified amounts of time are also contemplated. 
   At  708 , if the memory card has been accessed within the first specified amount of time, the card may remain powered up and flow may continue at  707 . 
   At  709 , if the memory card has not been accessed within a first specified amount of time, the card may be powered down. 
   At  715 , if the host controller attempts to access the card, at  719 , the card may be powered up and the flow may continue at  707 . 
   At  717 , if the host controller is not attempting to access the card, the card may be maintained in a power down state and the flow may continue at  715 . 
   At  711 , after the card reader has been electrically disconnected from the USB host controller, a determination may be made whether a card has been inserted into the card reader. 
   At  712 , if a card has not been inserted into the card reader, the card reader may be maintained in the electrically disconnected state, and flow may continue at  711 . 
   At  713 , if a card has been inserted into the card reader, the card reader may be electrically reconnected and flow may continue at  707 . 
     FIG. 8  illustrates a flowchart of an embodiment of a method for electrically disconnecting a hub from a USB host controller. It should be noted that in various embodiments of the methods described below, one or more of the steps described may be performed concurrently, in a different order than shown, or may be omitted entirely. Other additional steps may also be performed as desired. 
   At  801 , a determination may be made whether a device is coupled to the hub. In some embodiments, an attach detect logic may be implemented to detect whether any devices are coupled to the hub. 
   At  803 , if a device is not coupled to the hub, at  805 , the hub may be electrically disconnected from the USB host controller. In some embodiments, if a device is not coupled to the hub, the hub may be electrically disconnected after a wait period to give the user time to switch out devices, etc. If a device is coupled to the hub during the wait period, the hub may not be electrically disconnected. In some embodiments, an auto detach logic may be implemented to electrically disconnect the hub from the USB host controller. 
   At  807 , if a device is coupled to the hub, a connection may be maintained between the hub and the USB host controller and flow may continue at  803 . 
   At  809 , if a device has been attached to the hub after the hub was electrically disconnected from the USB host controller, at  811 , the hub may electrically reconnect to the host controller. 
   At  813 , if a device has not been attached to the hub, the hub may be maintained in an electrically disconnected state and the flow may continue at  809 . 
     FIG. 9  illustrates a flowchart of an embodiment of a method for regulating the CPU. It should be noted that in various embodiments of the methods described below, one or more of the steps described may be performed concurrently, in a different order than shown, or may be omitted entirely. Other additional steps may also be performed as desired. 
   At  901 , a determination may be made whether there are any USB devices connected to the USB host controller. 
   At  903 , if there is a device coupled to the USB host controller, a connection between the device and the USB host controller may be maintained, and at  905 , the CPU may be maintained in an active state. 
   At  907 , if there are no devices coupled to the USB host controller, the USB host controller may not place a signal on the PCI bus. In some embodiments, if there is no activity on the PCI bus and other conditions for putting the CPU in a low power state are met, the CPU may go into a low power state. 
     FIG. 10  illustrates a flowchart of an embodiment of a method for regulating a CPU while attached to a hub. It should be noted that in various embodiments of the methods described below, one or more of the steps described may be performed concurrently, in a different order than shown, or may be omitted entirely. Other additional steps may also be performed as desired. 
   At  1001 , a determination may be made whether any USB devices are coupled to the hub. 
   At  1003 , if there are USB devices coupled to the hub, a connection may be maintained between the hub and the USB host controller, and at  1005 , the CPU may be maintained in the active state. 
   At  1007 , if there are no USB devices coupled to the hub, the hub may electrically disconnect from the USB host controller. 
   At  1009 , the USB host controller may not place a signal on the PCI bus. In some embodiments, if there is no activity on the PCI bus and other conditions for putting the CPU in a low power state are met, the CPU may go into a low power state. 
   As used herein, a memory medium may include any of various types of memory devices or storage devices. The term “memory medium” is intended to include an installation medium, e.g., a CD-ROM, floppy disks  104 , or tape device; a computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc.; or a non-volatile memory such as a magnetic media, e.g., a hard drive, or optical storage. The memory medium may comprise other types of memory as well, or combinations thereof. In addition, the memory medium may be located in a first computer in which the programs are executed, or may be located in a second different computer which connects to the first computer over a network, such as the Internet. In the latter instance, the second computer may provide program instructions to the first computer for execution. The term “memory medium” may include two or more memory mediums which may reside in different locations, e.g., in different computers that are connected over a network. In addition, as used herein, a carrier medium—a memory medium as described above, as well as signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as a bus, network and/or a wireless link. The computer system  101  may include a memory medium(s) on which one or more computer programs or software components according to one embodiment of the present invention may be stored. For example, the memory medium may comprise a read only memory or programmable read only memory such as an EEPROM, or flash memory that stores a software program (e.g., firmware) that is executable to perform the methods described herein. Various embodiments further include receiving or storing instructions and/or data implemented in accordance with the foregoing description upon a carrier medium. 
   Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following requests.