Patent Publication Number: US-7917679-B2

Title: Trusted LPC docking interface for docking notebook computers to a docking station

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to computer systems, and more particularly, to portable computer systems that may be coupled to a docking station. 
     2. Description of the Related Art 
     Portable computers enjoy widespread popularity. Advances in computer technology, such as faster processors with low power consumption, have led to portable computer systems that are comparable to desktop computers in performance. Because of these improvements, portable computers are an ideal solution for a user that needs a large amount of computing power as well as a mobile platform. 
     Despite the performance increases, portable computers still are at a disadvantage relative to other computers. In particular, due to their small size, portable computers typically are not able to offer as much functionality as stationary computers, as a limited number of interfaces are present. One solution to this problem is a docking station. A docking station may allow for increased functionality when the portable computer is coupled to it. Through a docking station, a portable computer may be able to utilize the functionality of such devices as a full-screen monitor, additional printers, scanners, and so forth. 
     Although docking stations are a convenient solution to providing additional functionality for a portable computer, coupling the portable computer to a docking station may introduce a new set of issues that require attention. One such issue has arisen due to new industry requirements for security in computers, and specifically notebook computers using “LPC (Low Pin Count) Docking”. In many cases it may be required to protect information passing through a docking interface such that the information does not become accessible outside of the notebook computer. 
     Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein. 
     SUMMARY OF THE INVENTION 
     A method and apparatus for operating a portable computer coupled to a docking station is disclosed. In one embodiment, the portable computer system includes a bus bridge and a bus coupled to the bus bridge. One or more peripheral devices or peripheral interfaces may be coupled to the bus. The bus may also be coupled to a docking interface. The docking interface may be an integrated circuit having a bus switch. The docking interface may be adapted to couple the bus to a peripheral interface in the docking station. When the bus switch is closed, after the computer is coupled to the docking station, the bus may be coupled to the peripheral interface, via a docking connector in the portable computer and a complementary connector in the docking station. The bus switch may close responsive to the docking, thereby completing the electrical coupling of the bus to the peripheral interface in the docking station. In one set of embodiments, the closing of the bus switch may be controlled by the docking interface such that operations on the bus are not suspended during docking operations. 
     In one embodiment, the bus may be a low pin count (LPC) bus. The bus switch may be a low on-resistance, high off-resistance bi-directional switch that may close to electrically couple the LPC bus to the docking connector. The docking station may include a complementary connector configured to be coupled to the docking connector of the portable computer. The complementary connector in the docking station may be electrically coupled to at least one peripheral interface. When the portable computer is connected to the docking station, a dock detect signal may be asserted and received by the docking interface. The docking interface may then initiate a sequence of events that result in the bus switch closing, thereby connecting the bus in the portable computer to the peripheral interface in the docking station. In one set of embodiments, the sequence of events that results in the closing of the bus switch may be performed without suspending operations on the bus. 
     In one set of embodiments, in order to support trusted LPC cycles, the bus switch may be configured to block trusted LPC cycles from being seen outside the docking interface during operation of the portable computers once the portable computer has been coupled to the docking station. The bus switch may comprise multiple switches, and once docking has been enabled, the switches may be closed. Subsequently, each LPC cycle may be tracked and a determination may be made at the beginning of each LPC cycle whether certain specified switches need to be opened or need to remain closed. In one embodiment, the start of a trusted LPC cycle is recognized upon receiving a special code indicative of a trusted LPC cycle, and after having ascertained that the LPC cycle is a trusted LPC cycle certain specified switches are opened. The specified switches may then be closed at the end of each trusted LPC cycle, or any time a trusted LPC cycle is aborted. In some embodiments, a trusted LPC cycle may be aborted by receiving a new information packet/frame prior to the trusted LPC cycle completing. 
     It should be noted that bus types other than the LPC bus are possible and contemplated for the method and apparatus described herein. Other types of buses may include, but are not limited to, a peripheral component interconnect (PCI) bus, an industry standard architecture or extended industry standard architecture (ISA/EISA) bus, universal serial bus (USB), general purpose instrument bus (GPIB), advanced graphics port (AGP), and so forth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
         FIG. 1  is a drawing illustrating one embodiment of a portable computer and a docking station; 
         FIG. 2  is a block diagram of one embodiment of a portable computer system and a docking station, wherein the portable computer system is configured for preventing information transmitted during trusted bus cycles to be accessible outside the portable computer system with the portable computer system docked to the docking station; 
         FIG. 3  is a flow diagram illustrating one embodiment of a method for docking a portable computer to a docking station; 
         FIG. 4  is a diagram illustrating one embodiment of a switching circuit configured in a bus switch comprised in a portable computer system configured for preventing information transmitted during trusted bus cycles to be accessible outside the portable computer system with the portable computer system docked to the docking station; 
         FIG. 5  is a timing diagram illustrating a successfully completed trusted LPC write sequence according to one embodiment; 
         FIG. 6  is a timing diagram illustrating a successfully completed trusted LPC read sequence with no long synchronization pulses according to one embodiment; 
         FIG. 7  is a timing diagram illustrating a successfully completed trusted LPC read sequence with long synchronization pulses according to one embodiment; and 
         FIG. 8  is a timing diagram illustrating an aborted trusted LPC read sequence with long synchronization pulses according to one embodiment. 
         FIG. 9  is a flow diagram illustrating one embodiment of a method for interfacing devices to a bus. 
     
    
    
     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 description thereto are not intended to limit the invention to the particular form disclosed, but, on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling with the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The Intel® LPC Interface Specification, Revision 1.0, Sep. 29, 1997, is incorporated by reference herein in its entirety. 
     U.S. patent application Ser. No. 10/076,105 titled “Switched Hot Docking Interface” invented by Richard Boz, Ronald Streiber, John Virzi and Richard Wahler, and filed on Feb. 14, 2002, is hereby incorporated by reference in its entirety as though fully and completely set forth herein. 
       FIG. 1  is a drawing of one embodiment of a portable computer and a docking station. Portable computer  100  may be one of many different types of portable computers (i.e. laptops, notebooks, etc.). Furthermore, it is possible and contemplated that portable computer  100  may be another type of device, such as a personal digital assistant (PDA). 
     Docking station  120  may provide additional functionality to portable computer  100 . Docking station  120  may include connections for a full-size keyboard, a monitor, a printer, and various other peripheral devices. Docking station may be able to provide the use of a full-size keyboard and monitor display when portable computer  100  is coupled to docking station  120 . Various types of peripheral bus interfaces may be employed, including universal serial bus (USB), peripheral component interconnect (PCI), and/or similar bus interfaces well known in the art. Through the various interfaces in both portable computer  100  and docking station  120 , the use of various devices such as flatbed and feed-through scanners, high capacity disk drives (e.g. a ZIP drive or external USB hard drive), network interfaces, printers, joysticks, a trackball or mouse, and many other devices may be employed. Although portable computer  100  may include some of the same types of interfaces as docking station  120 , the docking station may provide additional interfaces, thereby expanding the functionality of the portable computer. 
     In one set of embodiments, portable computer  100  may also be configured for hot-docking to docking station  120 . In other embodiments hot-docking may not be a requirement and power may be interrupted prior to docking portable computer  100  to docking station  120 . Hot-docking may be defined here as coupling portable computer  100  to docking station  120  without an interruption in power when the computer is not in suspend mode or hibernation mode. In the embodiment shown, it may be unnecessary to power down or suspend power to portable computer  100  when coupling it to docking station  120 . Furthermore, portable computer  100  may be configured to continue operations without interruption during hot-docking operations. Continuing operations may include transactions on a bus configured to electrically couple to docking station  120  as a result of hot-docking operations. Thus, operations on a bus in portable computer  100  may continue uninterrupted even while the bus is electrically coupled to docking station  120 . 
     In one set of embodiments, portable computer  100  may be further configured to be undocked from docking station  120  without removing power. Bus transactions within portable computer  100  may continue uninterrupted during undocking operations, even after communications with docking station  120  have been terminated. Docking station  120  may be powered down responsive to the undocking. 
     Turning now to  FIG. 2 , a block diagram is shown of one embodiment of portable computer system  100  and docking station  120 , wherein portable computer  100  may be configured for hot-docking to docking station  120 . Portable computer  100  may include bus bridge  104  and docking interface  102 , which may be coupled to each other via bus  103 . Bus  103  may be a low pin count (LPC) bus in one embodiment, although other embodiments are possible and contemplated. As noted above, the Intel® LPC Interface Specification, Revision 1.0, Sep. 29, 1997, is incorporated by reference herein in its entirety. Other possible bus types may include a peripheral component interconnect (PCI) bus, an industry standard architecture/extended industry standard architecture (ISA/EISA) bus, an advanced graphic port (AGP) bus, a universal serial bus (USB), a general purpose instrument bus (GPIB) or other bus types well known in the art and configurable for interfacing portable computers with peripheral devices and/or docking stations. 
     Bus  103  may also be coupled to peripheral interfaces  110  and  112 . Peripheral interfaces may allow devices to be coupled to portable computer  100 , and in some cases, may be devices that are actual components of portable computer  100 . Such devices may include, but are not limited to, disk drives, modems, network interfaces, Universal Asynchronous Receiver-Transmitters (UARTs), Parallel Ports, Floppy Disk, and similar peripherals well known in the art. Bus  103  may allow peripheral interfaces  110  and  112  to communicate with a processor (not shown) and a memory system (not shown) in portable computer  100 . It should be noted that the portion of the bus that is actually coupled to the docking station (to the right of the switch in the drawing) may be referred to as a switched bus. 
     Computer system  100  also includes clock driver  106 . Clock driver  106  may be coupled to bus bridge  104  by utility bus  109 . Bus bridge  104  may send commands over utility bus  109  to clock driver  106  to enable or disable the clock driver outputs. In the embodiment shown, clock driver  106  has two clock outputs, one for driving a clock signal to docking interface  102  and one for driving a clock signal to docking station  120 . Additional clock outputs for driving clock signals to other devices in portable computer system may also be present. 
     Portable computer  100  may include docking connector  114 , which may be configured to couple to complementary connector  121  in docking station  120 . When coupled together, docking connector  114  and complementary connector  121  may provide physical and electrical connections between portable computer  100  and docking station  120 . At least one signal path through docking connector  114  may be configured to provide a dock detect signal to docking interface  102 . In the embodiment shown, the dock detect signal is asserted in a logic low state. The dock detect signal may normally be pulled to a logic high state by resistor  118 , which may be coupled to a power node in portable computer  100 . When docking portable computer  100  to docking station  120 , the signal line associated with the dock detect signal may be coupled to a ground node, thereby causing the dock detect signal to be asserted in a logic low state. Other embodiments are possible and contemplated wherein the dock detect signal is asserted in a logic high state, and/or wherein a pull-up or pull down resistor is configured in docking station  120 . 
     Docking connector  114  may also include power pin  113 . In some embodiments, docking station  120  may be configured to receive power from portable computer  100 . In the embodiment shown, power pin  113  provides a path for power from a power node of portable computer  100  to docking station  120 . In some embodiments, multiple power pins may be present, as well as corresponding multiple ground pins. In other embodiments, docking station  120  may receive power from an external source separate from portable computer  100 . In such embodiments, power pin  113  may be used to convey a signal to initiate a power-up sequence in docking station  120 . Additional embodiments are possible and contemplated wherein the mere act of coupling portable computer  100  to docking station  120  causes power-up sequence to be executed in docking station  120 . The power-up sequence may turn on power received from portable computer  100 , or power received from another external source. 
     As previously noted, docking interface  102  may be configured to receive a dock detect signal. When docking interface  102  detects an assertion of the dock detect signal, it may begin operations to electrically couple bus  103  to peripheral interface chip  122  in docking station  120 . In the embodiment shown, peripheral interface chip  122  is a single chip with multiple interfaces. Other embodiments are possible and contemplated wherein multiple interface chips are present (and configured to couple to bus  103  when portable computer  100  is docked to docking station  120 ). Furthermore, such interface chips may include a single interface or multiple interfaces. In the embodiment shown, peripheral interface chip  122  includes serial port  124  and parallel port  126 . Serial port  124  is shown here coupling to peripheral device  132 , while parallel port  126  is shown here coupling to peripheral device  130 . 
     Docking interface  102  may include bus switch  107  coupled to bus  103 , and switch control circuit  117  and cycle monitoring circuit  119  both coupled to bus  103  on one side of bus switch  107 . In one embodiment, bus switch  107  is a low on-resistance, high off-resistance bi-directional switch. Bus switch  107  may also be configured to comprise multiple individual switches. Switch control circuit  117  may include a translation circuit  123  for translating various bus commands into open and close commands for bus switch  107 . In one embodiment, switch control circuit  117  may receive ‘write’ commands via bus  103 . The translation circuit  123  in switch control circuit  117  may translate these commands to an ‘open’ or ‘close’ command. Switch control circuit  117  may open or close bus switch  107  depending upon the command received. In one embodiment, cycle monitoring circuit  119  is configured to monitor bus cycles that occur on bus  103 , and determine whether a given bus cycle is a trusted bus cycle. As used herein, a ‘trusted bus cycle’ refers to a bus cycle wherein information transmitted during the bus cycle is to be protected and is not to be made available outside the portable computer. However, a trusted bus cycle may also be defined as any special bus cycle that is to be treated differently from regular bus cycles, and other designations for trusted bus cycles are possible and are contemplated. Cycle monitoring circuit  119  may further be configured to provide a signal indicative of a trusted bus cycle to bus switch  107  if a bus cycle has been determined to be a trusted bus cycle. In one set of embodiments, cycle monitoring circuit  119  may operate in conjunction with switch control circuit  117  to open or close bus switch  107  depending upon the command received, and whether the command is part of a trusted bus cycle. 
     When docking interface  102  detects an assertion of the dock detect signal, it may initiate a sequence of events that result in the closing of bus switch  107 . This sequence of events may include docking interface  102  communicating with bus bridge  104  to indicate that computer system  100  is coupled to docking station  120 . Such communication may be performed over bus  103 , or, in other embodiments, over separate signal lines that couple docking interface  102  to bus bridge  104 . Bus bridge  104  may respond by forwarding one or more commands to translation circuit  123  within switch control circuit  117 . These commands may be translated and may cause switch control circuit  117  to close bus switch  107 . The commands may include timing and/or other information that allows the closing of bus switch  107  to be precisely timed. In order to ensure the proper timing, clock driver circuit  106  may begin driving a clock signal to docking station  120 . This may allow for proper synchronization of transactions occurring between portable computer  100  and docking station  120  following the closing of bus switch  107  and subsequent utilization of docking station peripherals by portable computer  100 . The closing of bus switch  107  may be performed in such a manner as to prevent or minimize electrical transients on bus  103 . Precise control of the closing of bus switch  107  by switch control circuit  117  may allow the switch to be closed without any significant disturbance to current traffic on bus  103  (e.g. a transaction between bus bridge  104  and peripheral interface  110 ). In embodiments where bus cycles are monitored, cycle monitoring circuit  119  may operate in conjunction with switch control circuit  117  to open and/or close portions of the switches comprised in bus switch  107 , depending on whether a bus cycle is a trusted bus cycle. 
     When bus switch  107  is closed, bus  103  may be electrically coupled to peripheral interface chip  122  in docking station  120 . This may allow portable computer  100  to take advantage of the extra functionality provided by docking station  120 . With bus switch  107  closed, bus bridge  104  may have a communications link to peripheral interface chip  122 , and hence any peripheral devices coupled to it (e.g. peripheral devices  130  and  132 ). 
     Docking interface  102  may be further configured to initiate undocking procedures when it is desired to undock portable computer  100  from docking station  120 . The initiation of undocking procedures may be a result of an input from a user of portable computer  100 . For example, a user may select an “eject” option from a start menu of an operating system running on computer  100 . This may eventually cause commands to be sent to the translation circuit in switch control circuit  117 . Pending transactions between docking station  120  and portable computer  100  may be allowed to complete in some instances, or may be terminated in other instances. Once all transactions have been completed or terminated, switch control circuit  117  may open bus switch  107 , thereby disconnecting bus  103  from peripheral interface  122  in docking station  120 . It should be noted that the timing of events related to opening bus switch  107  may be similar or identical to the timing necessary for closing the switch. 
     Moving now to  FIG. 3 , a flow diagram illustrating one embodiment of a method for docking a portable computer to a docking station is shown. Method  200  may allow a portable computer such as portable computer  100  to be coupled to a docking station such as docking station  120 . Furthermore, method  200  may allow for hot-docking a portable computer to a docking station. It should be noted that other embodiments including a greater or lesser number of items, or different items, are possible and contemplated. 
     In the embodiment of the method shown, a portable computer is physically coupled to the docking station ( 202 ). The physical coupling of a portable computer to a docking station may comprise the coupling of a connector on the portable computer to a complementary connector on a docking station. This may provide the physical/electrical connections that are necessary in order for the portable computer to utilize the extra functionality provided by the docking station. When the portable computer system is coupled to the docking station, a dock detect signal may be asserted ( 204 ). The dock detect signal may be received by the portable computer. In one embodiment, the dock detect signal may be received by a docking interface such as docking interface  102  of  FIG. 2 . When received by the docking interface or other device, the portable computer may initiate a sequence of events that allows it to become functionally coupled to the docking station. 
     Following the assertion and detection of the dock detect signal, a power up sequence in the docking station may be initiated ( 206 ). The power up sequence may include the portable computer supplying power to the docking station in some embodiments, while other embodiments may include the docking station receiving power from another external source. It should be noted that, in some embodiments, the docking station may be powered up prior to docking, and thus no power up sequence may be necessary. When the docking station is fully powered up, it may assert a signal to indicate that it has been powered up successfully (i.e. a ‘power ok’ signal). The signal may be received by the portable computer, which may begin other operations in order to initialize bus connections with the docking station, thereby allowing the portable computer to utilize additional peripheral functions. 
     Initializing bus connections between the portable computer and the docking station may include sending commands to a switch control circuit ( 208 ). Using the example shown in  FIG. 2 , switch control circuit  117  may be configured to receive a command from bus bridge  104 . More particularly, bus bridge  104  may be configured to send commands to a translation circuit within switch control circuit  117 . The commands may cause the switch control circuit to close a bus switch (item  210 ). In one set of embodiments, the closing of the bus switch may be timed such that the closing of the switch does not significantly affect any transactions occurring on the bus. Thus, again using  FIG. 2  as an example, a transaction on bus  103  between peripheral device  110  and bus bridge  104  may continue even during the closing of switch  107 . 
     As previously noted, in one embodiment, the bus may be an LPC bus. The LPC bus may include a ‘turnaround’ phase, or cycle. The turnaround cycle, in one embodiment, may be two system clock cycles in width, and may be initiated when the bus bridge is turning control of the bus over to a peripheral device, or when the peripheral device is returning control of the bus to the bus bridge. During a write cycle to the translation circuit, which may be implemented as a register in one embodiment, two turnaround cycles may occur. The first turnaround cycle may occur when a command is written to the register. At the beginning of the second turnaround cycle, as control of the bus is returned to the bus bridge, the switch may close, thereby electrically coupling the bus to the peripheral interface in the docking station. 
     Once the bus switch has been closed, the portable computer may begin operations with the docking station ( 212 ). More particularly, the bus may be used to communicate with peripherals in the portable computer and peripherals in the docking station. Thus, the portable computer may utilize extra functionality provided by the docking station. As previously noted, alternative methods to method  200  for docking the portable computer to the docking station are possible and are contemplated. 
     Moving now to  FIG. 4 , one embodiment of a switching circuit  400  configured in bus switch  107 , (of  FIG. 2 ), is shown. In this embodiment, bus switch  107  comprises LPC dock switch  402 , which itself comprises switches S 0  through S 3  coupling signal lines LAD 0 -LAD 3  to signal lines DLAD 0 -DLAD 3 , respectively. Signals LAD 0 -LAD 3  may be signals transmitted over bus  103  (of  FIG. 2 ). A dock control signal  412  and trusted cycle signal  414  may be coupled to AND gate  422 , with the output of AND gate  422  configured to operate as a control signal enabling/disabling switches S 0 -S 3 . In one embodiment, dock control signal  412  is generated by and received from translation circuit  123  configured within switch control circuit  117  (of  FIG. 2 ), and trusted cycle signal  414  is generated by and received from bus monitor circuit  119  (also of  FIG. 2 ). Dock control signal  412  may also be configured to enable/disable, independently of LPC dock switch  402 , switch  424  connecting signal line  410  to signal line  416 , carrying, in this embodiment, LFRAME# signal indicative of transmission of a new frame of information. It should be noted that AND gate  422  and inverter  420  are shown for illustrative purposes, and alternative configurations for controlling switches S 0 -S 3  and switch  424  via dock control signal  412  and trusted cycle signal  414  are possible and are contemplated. In one set of embodiments, switch  424  may be used for coupling signals that are not interrupted during any portion of a trusted cycle, while switches S 0 -S 3  in LPC dock switch  402  may be used for coupling signals that may be interrupted during at least a portion of the trusted cycle. 
       FIG. 5  is a timing diagram for illustrating a successfully completed operating sequence, which may be a trusted LPC write sequence (also referred to as a trusted write cycle), for one embodiment of a portable computer system configured for docking with a docking station. The operating sequence may take place once the computer has already been docked to the docking station. The embodiment shown is an exemplary embodiment, and other embodiments are possible and contemplated. Other embodiments may include additional signals not shown here, and may not include some of the signals that are shown here. Furthermore, the states of assertion (logic high or logic low) may be different for various embodiments. 
     In the embodiment shown in  FIG. 5 , a trusted write cycle may be identified by an LFRAME# signal, such as LFRAME# signal  410  in  FIG. 4 , being asserted and by a special code simultaneously transmitted over LAD[ 3 : 0 ] lines that may carry data and/or address information, such as signal lines LAD 0 -LAD 3  in  FIG. 4 . In the illustrated embodiment the special code is shown as “YYYY” and is indicative of a trusted bus cycle. Information immediately following the special code on the LAD[ 3 : 0 ] signal lines may be indicative of the type of bus operation, in this case a write operation. This may be followed by data associated with the bus operation, also on the LAD[ 3 : 0 ] signal lines. In one embodiment, upon recognizing from the special code that a trusted bus cycle is taking place, a trusted cycle signal, such as trusted cycle signal  414  in  FIG. 4 , is asserted and remains asserted until the trusted write cycle has completed as designated by the appropriate codes transmitted over signal lines LAD[ 3 : 0 ]. Asserting the trusted cycle signal may result in signal lines DLAD[ 3 : 0 ], such as signal lines DLAD 0 -DLAD 3  in  FIG. 4 , being tri-stated, thus preventing information transmitted over signal lines LAD[ 3 : 0 ] from being passed on to signal lines DLAD[ 3 : 0 ]. Upon completion of the trusted cycle, as designated by the correspondingly indicative information received over signal lines LAD[ 3 : 0 ], the trusted cycle signal may be de-asserted and information transmitted over signal lines LAD[ 3 : 0 ] may again be passed on to signal lines DLAD[ 3 : 0 ] as illustrated in  FIG. 5  by data ‘1111’ appearing on signal lines LAD[ 3 : 0 ] being mirrored on signal lines DLAD[ 3 : 0 ]. 
       FIG. 6  and  FIG. 7  show timing diagrams illustrative of a successfully completing trusted read cycle with no long synchronization pulses and a successfully completing trusted read cycle with long synchronization pulses, respectively, for one embodiment of a portable computer system configured for docking with a docking station. In the embodiment shown in  FIG. 6 , a trusted read cycle may be identified in a manner similar to identifying a trusted write cycle, by the LFRAME# signal being asserted and by the special code simultaneously transmitted over signal lines LAD[ 3 : 0 ], the special code followed by information indicative of a read operation. The special code is again shown as “YYYY” and is again indicative of a trusted bus cycle. The trusted cycle signal may again be asserted in a manner similar to that shown in  FIG. 5 , again resulting in signal lines DLAD[ 3 : 0 ] being tri-stated, thus preventing information transmitted over signal lines LAD[ 3 : 0 ] from being passed on to signal lines DLAD[ 3 : 0 ] during the trusted cycle. The embodiment shown in  FIG. 7  is similar to that shown in  FIG. 6 , with the exception of additional long synchronization pulses transmitted over signal lines LAD[ 3 : 0 ] prior to completing the trusted read cycle, the synchronization pulses shown in  FIG. 7  as data labeled ‘0110’. 
     For the embodiments of both  FIG. 6  and  FIG. 7 , similar to the embodiment of  FIG. 5 , upon completion of the trusted cycle, as designated by the correspondingly indicative information received over signal lines LAD[ 3 : 0 ], the trusted cycle signal may be de-asserted and information transmitted over signal lines LAD[ 3 : 0 ] may again be passed on to signal lines DLAD[ 3 : 0 ] as illustrated in both  FIG. 6  and  FIG. 7  by data ‘1111’ appearing on signal lines LAD[ 3 : 0 ] being mirrored on signal lines DLAD[ 3 : 0 ]. 
       FIG. 8  shows a timing diagram of an aborted trusted read cycle for one embodiment of a portable computer system configured for docking with a docking station. The embodiment of  FIG. 8  differs from the embodiment of  FIG. 7  in that LFRAME# may be asserted before information indicative of the completion of the trusted cycle could be received over signal lines LAD[ 3 : 0 ], leading to the trusted cycle signal being de-asserted in response and information transmitted over signal lines LAD[ 3 : 0 ] being passed on to signal lines DLAD[ 3 : 0 ]. 
     Considering the timing diagrams of  FIGS. 5 ,  6 ,  7 , and  8  in view of the corresponding signals in the embodiment of  FIG. 4 , information transmitted over signal lines LAD 0 -LAD 3  may be passed on to signal lines DLAD 0 -DLAD 3  any time LFRAME# signal  410  is unasserted. Whenever a special code indicating a trusted cycle is detected when LFRAME# signal  410  transitions from an unasserted state to an asserted state, signal lines DLAD 0 -DLAD 3  may be tri-stated (or disconnected as shown) and may remain tri-stated (or disconnected) until either the end of the trusted cycle is detected or LFRAME# signal  410  is asserted, whichever event may take place first. While the embodiments discuss tri-stating and/or opening a switch as the preferred method for preventing information on signal lines LAD 0 -LAD 3  from being passed on to signal lines DLAD 0 -DLAD 3 , methods other than tri-stating and/or opening a switch for preventing information on signal lines LAD 0 -LAD 3  from being passed on to signal lines DLAD 0 -DLAD 3  are possible and are contemplated. 
     Considering again the timing diagrams of  FIGS. 5 ,  6 ,  7 , and  8  in view of the corresponding signals in the embodiment of  FIG. 4 ,  FIG. 9  illustrates one embodiment of a method  900  for interfacing devices, for example a docking station and/or devices comprised in the docking station, to a bus while giving special consideration to specified, for example trusted, bus cycles. One or more devices may be coupled to the bus ( 902 ) and cycles on the bus may be monitored through receiving signals and commands over the bus ( 904 ). For example, cycle monitoring circuit  119  of  FIG. 2  may be monitoring signals and commands received over bus  103 , also of  FIG. 2 . In response to receiving certain commands, for example a write command as shown in  FIG. 5 , a determination may be made whether the current bus cycle is of a certain type, for example a trusted bus cycle ( 906 ). If it is determined, for example, that the bus cycle is indeed a trusted bus cycle, one or more of the one or more devices may be electrically decoupled from the bus ( 908 ). By way of example, in the embodiment shown in  FIG. 4 , the decoupling comprises opening switches S 0 -S 3 . In response to the specified cycle, in this case a trusted bus cycle, being either aborted, completed, and/or interrupted, the one or more devices that were electrically decoupled from the bus may be electrically recoupled to the bus ( 910 ). Considering the embodiment in  FIG. 4  for example, interrupting a trusted read cycle, as illustrated in  FIG. 8 , would result in switches S 0 -S 3  being closed. Those skilled in the art will appreciate that while references regarding method  900  were made to various embodiments presented in  FIGS. 2 ,  4 ,  5  and  8 , method  900  may be equally employed in various alternate embodiments, which are not shown but are contemplated. 
     While the present invention has been described with reference to particular embodiments, it will be understood that the embodiments are illustrative and that the invention scope is not so limited. Any variations, modifications, additions, and improvements to the embodiments described are possible. These variations, modifications, additions, and improvements may fall within the scope of the inventions as detailed within the following claims.