Patent Publication Number: US-5835791-A

Title: Versatile connection of a first keyboard/mouse interface and a second keyboard/mouse interface to a host computer

Description:
BACKGROUND 
     This invention relates generally to personal computers and pertains particularly to a versatile keyboard controller. 
     Keyboard controllers for personal computers generally use an eight-bit microprocessor, such as an 8052 processor, to collect and pass data between the keyboard/mouse and a system processor, such as a Pentium processor. The interface between the system and the keyboard controller consists of two eight-bit registers (i.e., port 64/60) and two interrupt lines (IRQ1 and IRQ12). This interface was introduce with the IBM PC/AT personal computer and expanded to include the mouse in the IBM PS/2 personal computer. It is the de facto industry standard. 
     The universal serial bus (USB) is designed as an alternate standard to current keyboard controllers. Further, the USB is specified to interface to a multitude of device types, not just keyboards and mice. The host controller interface (HCI) to the USB controller consists of more than twenty 32-bit registers. All communication between the system processor and the USB controller is currently specified to operate at the operating system level. The system processor, via its USB driver, must perform a lengthy configuration with the USB controller before any device can become operational. For general information on the USB, see the Universal Serial Bus Specification, Revision 1.0, Jan. 19, 1996, by Compaq Computer Corporation, Digital Equipment Corporation, IBM PC Company, Intel Corporation, Microsoft Corporation, NEC and Northern Telecom. 
     Current implementations of USB utilize a USB controller rather than a keyboard controller. These implementations of the USB are not backwards compatible with keyboards and mice which operate with prior versions of the keyboard controller. Further, current implementations of the USB do not utilize the port 64/60, therefore application programs, such as certain game programs, which directly access port 64/60, do not work properly on a system which utilizes the USB. 
     SUMMARY OF THE INVENTION 
     In accordance with the preferred embodiment of the present invention, a keyboard controller supports both a first keyboard/mouse interface and a second keyboard/mouse interface. For example, the first keyboard/mouse interface is a universal serial bus serial interface and the second keyboard/mouse interface is a PS/2 serial interface. Data is routed between the first keyboard/mouse interface and a first host interface when the first host interface is active. For example, the first host interface is a host controller interface (HCI). Data is routed between the first keyboard/mouse interface and a first shell when a second host interface is active. The first shell provides compatible connection between the first keyboard/mouse interface and the second host interface. The second host interface is, for example, a port 64/60 interface. Data is routed between the second keyboard/mouse interface and the second host interface when the second host interface is active. Data is routed between the second keyboard/mouse interface and a second shell when the first host interface is active. The second shell provides compatible connection between the second keyboard/mouse interface and the first host interface. 
     In the preferred embodiment of the present invention, the second (USB) shell includes a virtual serial keyboard, a serial keyboard inbound queue, a serial keyboard outbound queue, a virtual mouse, a mouse inbound queue, and a mouse outbound queue. The second shell also includes a virtual matrix keyboard, a matrix keyboard inbound queue, and a matrix keyboard outbound queue. 
     Likewise in the preferred embodiment, the first shell includes a virtual keyboard, a first linked list of transfer descriptors for virtual keyboard data, a virtual mouse, and a second list of transfer descriptors for virtual mouse data. 
     The present invention provides for a versatile keyboard controller which supports USB keyboards and mice as well as the current industry standard. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a logic flow for a keyboard controller which supports both a universal serial interface and a PS/2 serial interface in accordance with the preferred embodiment of the present invention. 
     FIG. 2 shows logic flow for the keyboard controller shown in FIG. 1 when an HCI interface is active in accordance with the preferred embodiment of the present invention. 
     FIG. 3 shows a block diagram of a USB shell program in accordance with the preferred embodiment of the present invention. 
     FIG. 4 shows logic flow for the keyboard controller shown in FIG. 1 when a Port 64/60 interface is active in accordance with the preferred embodiment of the present invention. 
     FIG. 5 shows a block diagram of a PS/2 shell program in accords with the preferred embodiment of the present invention. 
     FIG. 6, FIG. 7, FIG. 8 and FIG. 9 are a flow chart which describes initialization of the keyboard controller shown in FIG. 1, in accordance with the preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a block diagram of logic flow through a keyboard controller 11 which supports both a universal serial bus (USB) interface and a PS/2 serial interface. Keyboard controller 11 receives input from a USB serial interface engine 16, a PS/2 serial interface 17, and/or matrix (unscanned) keyboard 18. Keyboard controller 11 interfaces with HCI registers 14 and/or a port 64/60 registers 15. 
     In a default mode a routing switch 19 and a routing switch 20 within keyboard controller 11 are set so that PS/2 serial interface 17 and any matrix (unscanned) keyboard 18 are connected to port 64/60 registers 15. USB serial interface engine 16 is routed through a PS/2 shell 13 to port 64/60 registers 15. PS/2 shell 13 allows USB devices connected to USB serial interface engine 16 to effectively communicate as PS/2 devices across port 64/60 registers 15. 
     If the operating system loads a USB driver, routing switch 19 and routing switch 20 within keyboard controller 11 are changed so that PS/2 serial interface 17 and any matrix (unscanned) keyboard 18 are routed through a USB shell 12 to HCI registers 14. USB serial interface engine is connected through to HCI registers 14. USB shell 12 allows PS/2 devices connected to PS/2 serial interface 17 and/or a matrix keyboard 18 to effectively communicate as USB devices across HCI registers 14. 
     FIG. 2 shows logic flow for the keyboard controller 11 when the HCI interface is active. An HCI interface handler 71 within keyboard controller 11 interfaces with HCI registers 14. USB serial interface engine 16 handles information from three ports: a port 74, a port 75 and a port 76. On the host side, USB shell 12 interfaces with HCI interface handler 71. On the port side, USB shell 12 interfaces with PS/2 serial interface 17 and PS/2 matrix keyboard handler 72. PS/2 serial interface 17 has a keyboard port 77 and a mouse port 78. PS/2 matrix keyboard handler 72 includes a matrix scanner 73 for scanning matrix keyboard 18. 
     FIG. 3 gives additional information of the operation of USB shell 12. USB shell 12 includes a USB virtual matrix keyboard block 87, a USB virtual serial keyboard block 88 and a USB virtual mouse block 89. PS/2 matrix keyboard inbound queue 101 queues PS/2 matrix keyboard inbound traffic 111 to be processed by USB virtual matrix keyboard 87 for transfer to HCI interface handler 71 along a data path 81. PS/2 matrix keyboard outbound queue 102 queues PS/2 matrix keyboard outbound traffic 112 received by USB virtual matrix keyboard 87 from HCI interface handler 71 along a data path 82. 
     PS/2 serial keyboard inbound queue 103 queues PS/2 serial keyboard inbound traffic 113 to be processed by USB virtual serial keyboard 88 for transfer to HCI interface handler 71 along a data path 83. PS/2 serial keyboard outbound queue 104 queues PS/2 serial keyboard outbound traffic 114 received by USB virtual serial keyboard 88 from HCI interface handler 71 along a data path 84. 
     PS/2 mouse inbound queue 105 queues PS/2 mouse inbound traffic 115 to be processed by USB virtual mouse 89 for transfer to HCI interface handler 71 along a data path 85. PS/2 mouse outbound queue 106 queues PS/2 mouse outbound traffic 116 received by USB virtual mouse 89 from HCI interface handler 71 along a data path 86. 
     FIG. 4 shows logic flow for the keyboard controller 11 when the port 64/60 interface is active. A port 64/60 interface 79 within keyboard controller 11 interfaces with port 64/60 registers 15. On the host side, PS/2 shell 13 interfaces with port 64/60 registers 15. On the port side, PS/2 shell 13 interfaces with USB serial interface engine 16. 
     FIG. 5 gives additional information of the operation of PS/2 shell 13. PS/2 shell 13 includes a PS/2 virtual serial keyboard block 129 and a PS/2 virtual mouse block 130. Inbound and outbound transactions for PS/2 virtual keyboard 129 are stored in a linked list of transfer descriptors. For example transfer descriptors 131, 132, 133 and 134 are shown. Transfer descriptor 131 includes inbound traffic 141 to be forwarded to port 64/60 registers 15 on a data path 121. Transfer descriptor 132 includes inbound traffic 142 to be forwarded to port 64/60 registers 15 on a data path 122. Transfer descriptor 133 includes outbound traffic 143 received from port 64/60 registers 15 on a data path 123. Transfer descriptor 134 includes inbound traffic 144 to be forwarded to port 64/60 registers 15 on a data path 124. An endpoint descriptor 130 is included at the end of the linked list of transfer descriptors. 
     Inbound and outbound transactions for PS/2 virtual mouse 130 are stored in a second linked list of transfer descriptors. For example transfer descriptors 135, 136, 137 and 138 are shown. Transfer descriptor 135 includes inbound traffic 145 to be forwarded to port 64/60 registers 15 on a data path 125. Transfer descriptor 136 includes outbound traffic 146 received from port 64/60 registers 15 on a data path 126. Transfer descriptor 137 includes outbound traffic 147 received from port 64/60 registers 15 on a data path 127. Transfer descriptor 138 includes inbound traffic 148 to be forwarded to port 64/60 registers 15 on a data path 128. An endpoint descriptor 140 is included at the end of the linked list of transfer descriptors. 
     FIG. 6, FIG. 7, FIG. 8 and FIG. 9 are a flow chart which describes initialization of keyboard controller 11 shown in FIG. 1, in accordance with the preferred embodiment of the present invention. In a step 21, which occurs at power-on, all USB ports are disabled. The preferred embodiment of the present invention supports three USB ports (i.e., USB ports 74, 75 and 76). 
     In a step 22 start of frame (SOF) generation is enabled. In a step 23, the USB keyboard device address is reset by resetting the variable &#34;USB --  KEYBD --  ADR&#34; to zero. In a step 24, the USB mouse device address is reset by resetting the variable &#34;USB --  MOUSE --  ADR&#34; to zero. 
     In a step 25, the variable &#34;PORT --  ADR&#34; is set equal to one. The variable &#34;PORT --  ADR&#34; is used to indicate the port currently being addressed. The three USB ports shown in FIGS. 2 and 3 are ports 74, 75 and 76. These are assigned port addresses (PORT --  ADR) of 1, 2 and 3, respectively. 
     In a step 26, the PS/2 serial keyboard device address is reset by resetting the variable &#34;PS/2 --  SERIAL --  KBD --  ADR&#34; to zero. In a step 27, the PS/2 matrix keyboard device address is reset by resetting the variable &#34;PS/2 --  MATRIX --  KBD --  ADR&#34; to zero. In a step 28, the PS/2 mouse device address is reset by resetting the variable &#34;PS/2 --  MOUSE --  ADR&#34; to zero. P/S2 devices, if found, will be assigned USB addresses. Since USB devices are point-to-point devices, the three possible PS/2 devices will &#34;appear&#34; on non-existent (virtual) ports, e.g., with port addresses of 4, 5 and 6. A connect 29 shows a connection between the flowchart from FIG. 6 to FIG. 7. 
     The flowchart portion shown in FIG. 7 starts with connect 29. In a step 30, the port specified by the variable &#34;PORT --  ADR&#34; is enabled. In a step 31, a determination is made as to whether there is a device attached to the port specified by the variable &#34;PORT --  ADR&#34;. If not, program flow jumps to step 37. 
     If there is a device attached to the port specified by the variable &#34;PORT --  ADR&#34;, in a step 32, a determination is made as to whether the device attached to the port specified by the variable &#34;PORT --  ADR&#34; is a slow speed device. If the device attached to the port specified by the variable &#34;PORT --  ADR&#34; is a slow speed device, in a step 34, the low speed bit in the HcRhPortStatus register is set to logic one. If the device attached to the port specified by the variable &#34;PORT --  ADR&#34; is not a slow speed device, in a step 33, the low speed bit in the HcRhPortStatus register is reset to logic zero. 
     In a step 35, the default device descriptor is read. This is a USB control transfer consisting of a setup, data and a status transaction. In a step 36 a determination is made as to whether the read of the default device descriptor in step 35 failed. If the read of the default device descriptor in step 35 did not fail, configuration continues via connect 40 to the portion of the flowchart shown in FIG. 8. 
     If the read of the default device descriptor in step 35 failed, in a step 37, the current port is turned off by disabling the current port specified by the variable &#34;PORT --  ADR&#34;. 
     In a step 38, a determination is made as to whether this is the last USB port (i.e., with a port address of 3). If this is not the last USB port, in a step 39, the variable &#34;PORT --  ADR&#34; is incremented and configurations continues via a return to step 30. If, in step 39, a determination is made that this is the last USB port, configuration continues via connect 41 to the portion of the flowchart shown in FIG. 9. 
     The flowchart portion shown in FIG. 8 starts with connect 40. The logic shown in FIG. 8 enables one USB keyboard (if found) and one USB mouse device (if found). In a step 51, a determination is made as to whether the default device is a keyboard. If so, in a step 52, a determination is made as to whether the variable &#34;USB --  KEYBD --  ADR&#34; equals zero. If the variable &#34;USB --  KEYBD --  ADR&#34; does not equal zero, this indicates that a USB keyboard has already been enabled. Therefore, since only one keyboard is allowed to be enabled, the flow jumps to step 55. 
     If in step 52 a determination is made that the variable &#34;USB --  KEYBD --  ADR&#34; equals zero, in a step 53, the keyboard is configured by setting the variable &#34;USB --  KEYBD --  ADR&#34; equal to the configuration address. 
     In a step 54, a determination is made as to whether the variable &#34;USB --  MOUSE --  ADR&#34; equals zero. If &#34;USB --  MOUSE --  ADR&#34; does not equal zero, this means that both a keyboard and a mouse have been enabled. Thus, configuration of the USB ports is done and configurations continues via connect 41 to the portion of the flowchart shown in FIG. 9. 
     If in step 54, it is determined that the variable &#34;USB --  MOUSE --  ADR&#34; equals zero, in a step 55, a determination is made as to whether this is the last USB port. If this is not the last USB port, in a step 56, the variable &#34;PORT --  ADR&#34; is incremented and configurations continues via connect 29 to the portion of the flowchart shown in FIG. 6. If, in step 55, a determination is made that this is the last USB port, configuration continues via connect 41 to the portion of the flowchart shown in FIG. 9. 
     If in step 51 it is determined the default device is not the keyboard, in a step 57, a determination is made as to whether the default device is a mouse. If in step 57 it is determined that the default device is not a mouse, control jumps to step 55. If in step 57 it is determined that the default device is a mouse, in a step 58, a determination is made as to whether the variable &#34;USB --  MOUSE --  ADR&#34; equals zero. If the variable &#34;USB --  MOUSE --  ADR&#34; does not equal zero, this indicates that a USB mouse has already been enabled. Therefore, since only one mouse is allowed to be enabled, the flow jumps to step 55. 
     If in step 58 a determination is made that the variable &#34;USB --  MOUSE --  ADR&#34; equals zero, in a step 59, the keyboard is configured by setting the variable &#34;USB --  MOUSE --  ADR&#34; equal to the configuration address. 
     In a step 60, a determination is made as to whether the variable &#34;USB --  KEYBD --  ADR&#34; equals zero. If &#34;USB --  KEYBD --  ADR&#34; does not equal zero, this means that both a keyboard and a mouse have been enabled. Thus, configuration of the USB ports is done and configurations continues via connect 41 to the portion of the flowchart shown in FIG. 9. 
     If in step 60, it is determined that the variable &#34;USB --  KEYBD --  ADR&#34; equals zero, the flow continues at step 55. 
     The flowchart portion shown in FIG. 9 starts with connect 41. The logic shown in FIG. 9 configures any PS/2 devices which are present. In a step 61 a determination is made as to whether a matrix keyboard is attached. If so, in a step 62, a USB configuration table is assigned to the matrix keyboard interface (A pin in the matrix keyboard interface is pulled low when the matrix keyboard is attached). The configuration table contains sufficient information to permit the emulation of a USB device by the matrix keyboard. The matrix keyboard appears on port 4. When it gets configured by the host&#39;s USB driver, the USB address assigned to the matrix keyboard is saved in the HCI interface handler. This address is needed so that traffic to the matrix keyboard is routed through USB shell 12. 
     In a step 63 a determination is made as to whether a serial keyboard is attached. If so, in a step 64, a USB configuration table is assigned to the serial keyboard interface (PS/2 echo commands are used to determine if a serial keyboard is plugged in). The configuration table contains sufficient information to permit the emulation of a USB device by the serial keyboard. The serial keyboard appears on port 5. When it gets configured by the host&#39;s USB driver, the USB address assigned to the serial keyboard is saved in the HCI interface handler. This address is needed so that traffic to the serial keyboard is routed through USB shell 12. 
     In a step 65 a determination is made as to whether a mouse is attached. If so, in a step 66, a USB configuration table is assigned to the mouse interface (PS/2 echo commands are used to determine if a mouse is plugged in). The configuration table contains sufficient information to permit the emulation of a USB device by the mouse. The mouse appears on port 6. When it gets configured by the host&#39;s USB driver, the USB address assigned to the mouse is saved in the HCI interface handler. This address is needed so that traffic to the mouse is routed through USB shell 12. Upon reaching step 67, initialization is complete. 
     Table 1 below sets out pseudo code which describes operation of port 64/60 interface handler 79. 
     
                       TABLE 1                                                     
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START:                                                                    
Execute PS/2 matrix scanner                                               
                 /***Any keystrokes detected will be                      
                 stored in the PS/2 matrix keyboard                       
                 queue***/                                                
Read port 64     /***The port 64/60 interface does not                    
                 issue any kind of command                                
                 requesting inbound traffic. Inbound                      
                 traffic to the host is put in the port 60                
                 register when it is available and when                   
                 port 60 is empty***/                                     
IF outbound traffic                                                       
Reset &#34;USB HOST ACTIVE&#34; flag                                              
                     /***This turns off the USB                           
                     shell***/                                            
Go to OUTBOUND PS/2  /***This section sends                               
                     traffic to an active PS/2                            
                     device***/                                           
IF USB host active                                                        
Go to PS/2 INBOUND to HCI                                                 
                     /***The USB shell is active                          
                     so a check is made for                               
                     inbound traffic. Any traffic                         
                     will be posted to USB shell                          
                     12***/                                               
Go to PS/2 USB to PORT 64/60                                              
                     /***The PS/2 shell is active                         
                     so a check is made for                               
                     inbound traffic. Any traffic                         
                     will be passed through to                            
                     port 60.***/                                         
OUTBOUND PS/2:                                                            
IF Keyboard traffic                                                       
IF USB Keyboard Active                                                    
        Go to PS/2 VIRTUAL                                                
                     /***This sends traffic to the                        
        KEYBD        PS/2 virtual keyboard (i.e.,                         
                     the USB keyboard as it                               
                     appears in PS/2 shell 13).                           
                     The traffic is handled                               
                     as described below.***/                              
        Go to DONE   /***This pass is                                     
                     complete***/                                         
IF PS/2 Keyboard Active                                                   
        Go to PS/2 KEYBD                                                  
                     /***This sends traffic to the                        
                     PS/2 keyboard. The traffic                           
                     is handled as in the                                 
                     customary manner.***/                                
        Go to DONE                                                        
                 /***This pass is complete***/                            
Go to PS/2 MATRIX KEYBD                                                   
                     /***This sends traffic to a                          
                     routine which handles                                
                     matrix keyboard traffic.***/                         
Go to DONE       /***This pass is complete***/                            
IF Mouse traffic                                                          
IF USB Mouse Active                                                       
        Go to PS/2 VIRTUAL                                                
                     /***This sends traffic to the                        
        MOUSE        PS/2 virtual mouse (i.e.,                            
                     the USB mouse as it                                  
                     appears in PS/2 shell 13).                           
                     The traffic is handled as                            
                     similarly to the way the                             
                     PS/2 virtual keyboard is                             
                     implemented.***/                                     
        Go to DONE   /***This pass is                                     
                     complete***/                                         
Go to PS/2 MOUSE     /***This sends traffic to the                        
                     PS/2 mouse. The traffic is                           
                     handled as in the customary                          
                     manner.***/                                          
Go to DONE       /***This pass is complete***/                            
Process Keyboard controller                                               
                     /***Traffic not directed to                          
command and/or data  either a keyboard or mouse                           
                     is processed by the                                  
                     keyboard controller. The                             
                     keyboard controller consists                         
                     primarily of diagnostics and                         
                     the turning on or of the                             
                     keyboard or mouse                                    
                     interfaces.***/                                      
Go to DONE           /***This pass is                                     
                     complete***/                                         
PS/2 INBOUND to 64/60:                                                    
                     /***This routine checks                              
                     PS/2 and USB devices for                             
                     inbound traffic to port                              
                     64/60 interface***/                                  
IF Port 60 NOT empty /***Wait until data can be                           
                     sent to the host via port 60                         
                     before checking if any data                          
                     is available***/                                     
Go to DONE           /***This pass is                                     
                     complete***/                                         
Access PS/2 virtual KBD in the                                            
                     /***This checks if there is                          
PS/2 shell           any traffic from the USB                             
                     keyboard***/                                         
IF inbound traffic                                                        
Get next character from transfer descriptor                               
Translate from USB to PS/2 code                                           
Put code in Port 60                                                       
Reset all active Keyboard Flags                                           
Set &#34;USB KBD ACTIVE&#34;                                                      
Update transfer descriptor pointer                                        
Go to DONE       /***This pass is complete***/                            
Access PS/2 virtual mouse in                                              
                 /***This checks if there is                              
the PS/2 shell   any traffic from the USB                                 
                 mouse***/                                                
IF inbound traffic                                                        
Get next character from transfer descriptor                               
Translate from USB to PS/2 code                                           
Put code in Port 60                                                       
Reset &#34;PS/2 MOUSE ACTIVE&#34; Flag                                            
Set &#34;USB MOUSE ACTIVE&#34;                                                    
Update transfer descriptor pointer                                        
Go to DONE       /***This pass is complete***/                            
Access PS/2 interface registers                                           
                     /***This checks if there is                          
                     any serial keyboard PS/2                             
                     traffic***/                                          
IF PS/2 Serial Keyboard traffic                                           
Put code in Port 60                                                       
Set &#34;PS/2 KBD ACTIVE&#34; Flag                                                
Reset all other active KBD Flags                                          
Go to DONE       /***This pass is complete***/                            
IF PS/2 Mouse Keyboard traffic                                            
Put code in Port 60                                                       
Set &#34;PS/2 MOUSE ACTIVE&#34; Flag                                              
Reset &#34;USB MOUSE ACTIVE&#34; Flag                                             
Go to DONE       /***This pass is complete***/                            
READ PS/2 Matrix Queue                                                    
IF inbound traffic                                                        
Put code in Port 60                                                       
Set &#34;PS/2 MATRIX ACTIVE&#34; Flag                                             
Reset all other active KBD Flags                                          
Go to DONE       /***This pass is complete***/                            
PS/2 INBOUND to HCI:                                                      
                 /***This routine checks PS/2 and                         
                 USB devices for inbound traffic to                       
                 the HCI interface***/                                    
Read PS/2 Serial Interface                                                
                 /***USB shell is active***/                              
IF PS/2 Serial Keyboard Traffic                                           
Queue PS/2 code to PS/2 Matrix Inbound Queue in USB                       
Shell 13.                                                                 
Go to HCI OUTBOUND to PS/2                                                
IF PS/2 Mouse Traffic                                                     
Queue PS/2 code to PS/2 Mouse Inbound Queue in USB                        
Shell 13.                                                                 
Go to HCI OUTBOUND to PS/2                                                
Read PS/2 Matrix keyboard queue                                           
IF Data Available                                                         
Queue PS/2 code to PS/2 Serial Keyboard Inbound Queue in                  
USB Shell 13                                                              
Go to HCI OUTBOUND to PS/2                                                
HCI OUTBOUND to PS/2                                                      
IF PS/2 Matrix Keyboard Outbound Queue has data                           
Send DATA to PS/2 MATRIX KEYBOARD                                         
IF PS/2 Serial Keyboard Outbound Queue has data                           
Send DATA to PS/2 SERIAL KEYBOARD                                         
IF PS/2 Mouse Outbound Queue has data                                     
Send DATA to PS/2 MOUSE                                                   
DONE:            /***This is the end of the routine***/                   
EXIT ROUTINE.                                                             
______________________________________                                    
 
    
     Table 2 below sets out pseudo code which describes operation of USB virtual serial keyboard block 88 as it appears in PS/2 shell 12. 
     
                       TABLE 2                                                     
______________________________________                                    
PS/2 VIRTUAL KEYBD:                                                       
IF Not Command     /***This checks Port 64 for                            
                     status***/                                           
IF Command Operation in Progress                                          
Go to GET DATA BYTE                                                       
Post &#34;RESEND&#34; Response                                                    
                   /***This is posted to Port                             
                     60***/                                               
Go to DONE         /***This pass is complete***/                          
IF Not a Valid Command                                                    
                   /***Valid commands are                                 
                     numbered from ED through                             
                     FF***/                                               
Post &#34;RESEND&#34; Response                                                    
                   /***This is posted to Port                             
                     60***/                                               
Go to DONE         /***This pass is complete***/                          
IF INDICATOR COMMAND                                                      
                   /Command ED***/                                        
Post &#34;ACK&#34; Response                                                       
                   /***Posted to Port 60***/                              
&#34;Command-In-Progress = &#34;Indicators&#34;                                       
Go to DONE         /***This pass is complete***/                          
IF READ.sub.-- ID COMMAND                                                 
                   /Command F2***/                                        
Post &#34;ACK&#34; Response                                                       
                   /***Posted to Port 60***/                              
Post Keyboard ID   /***There are several bytes of                         
                     storage maintained in this                           
                     logic for storing such things                        
                     as multi-byte scan code                              
                     translations and command                             
                     responses (i.e. keyboard                             
                     ID&#39;s)                                                
Go to DONE         /***This pass is complete***/                          
IF ENABLE COMMAND  /Command F4***/                                        
Post &#34;ACK&#34; Response                                                       
                   /***Posted to Port 60***/                              
Set &#34;Scanning&#34; Flag                                                       
Go to DONE         /***This pass is complete***/                          
IF DISABLE COMMAND /Command F5***/                                        
Post &#34;ACK&#34; Response                                                       
                   /***Posted to Port 60***/                              
Reset &#34;Scanning&#34; Flag                                                     
Go to DONE         /***This pass is complete***/                          
IF RESEND COMMAND  /***Command FE***/                                     
Resend &#34;LAST.sub.-- CHAR&#34;                                                 
                   /***Posted to Port 60. Every                           
                     time a character is loaded                           
                     into port 60 it is also saved                        
                     in &#34;LAST.sub.-- CHAR&#34; in case                        
                     the host issues a resend                             
                     command.***/                                         
Go to DONE         /***This pass is complete***/                          
IF SELECT SCAN CODE                                                       
                   /***Command F0***/                                     
TABLE                                                                     
Post &#34;ACK&#34; Response                                                       
                   /***Posted to Port 60***/                              
&#34;COMMAND.sub.-- IN.sub.-- PROGRESS&#34; = &#34;SCANCODE.sub.-- TBL&#34;               
Go to DONE         /***This pass is complete***/                          
IF SELECT TYPEMATIC                                                       
                   /Command F3***/                                        
RATE                                                                      
Post &#34;ACK&#34; Response                                                       
                   /***Posted to Port 60***/                              
&#34;COMMAND.sub.-- IN.sub.-- PROGRESS&#34; = &#34;TYPE.sub.-- RATE&#34;                  
Go to DONE         /***This pass is complete***/                          
IF RESET           /***Commmand FF***/                                    
Construct &#34;Reset&#34; transfer descriptor                                     
                 /***empty transfer descriptors                           
                   reside in the PS/2 shell                               
                   and are attached to the USB                            
                   keyboard&#39;s endpoint                                    
                   descriptor. They are filled-                           
                   in as needed.***/                                      
Construct Reset Response transfer descriptor                              
Attach transfer descriptor to PS/2 endpoint descriptor                    
Go to DONE         /***This pass is complete***/                          
Post `ACK` Response                                                       
                   /**Ignore USB unsupported                              
                     stuff**/                                             
Go to DONE         /***This pass is complete***/                          
GET DATA BYTE:                                                            
Get a data byte    /***Read Port 60***/                                   
IF Indicator Operation                                                    
Construct &#34;Indicator&#34; Transfer Descriptor                                 
Construct Indicator Response transfer descriptor                          
Attach transfer descriptor to PS/2 endpoint descriptor                    
Go to DONE         /***This pass is complete***/                          
Post `ACK` Response                                                       
                   /**Ignore Typematic rate, and                          
                     scan code table                                      
                     operations***/                                       
DONE:              /***This is the end of the                             
                     routine***/                                          
EXIT ROUTINE.                                                             
______________________________________                                    
 
    
     Table 3 below sets out pseudo code which describes operation of HCI interface handler 71. 
     
                       TABLE 3                                                     
______________________________________                                    
START HCI INTERFACE:                                                      
IF NOT USB Operational State                                              
Go to USB INACTIVE                                                        
                 /***USB traffic is normally disabled                     
                   until the controller is put into                       
                   the USB operational state by the                       
                   Host***/                                               
Set &#34;USB Host Active&#34; Flag                                                
PROCESS NEXT LIST:                                                        
                 /***An entry point from below***/                        
IF Process Periodic lists                                                 
IF Not Last Endpoint Descriptor processed                                 
Get next Endpoint Descriptor from Periodic List                           
Get next Transfer Descriptor (From Endpoint)                              
ELSE                                                                      
Get next Endpoint Descriptor from Non-Periodic List                       
Get next Transfer Descriptor (From Endpoint)                              
IF Transfer Descriptor Exists                                             
IF PS/2 Device                                                            
Go to PS/2 DEVICE HANDLER                                                 
Perform transfer on USB Wire                                              
COMPLETE TRANSFER                                                         
                 /***This is a return point for PS/2                      
                   DEVICE HANDLER***/                                     
IF transfer complete                                                      
Put Transfer Descriptor in Done Queue                                     
IF Not End of Frame                                                       
Go to PROCESS NEXT LIST                                                   
DONE:            /***This is the end of the routine***/                   
EXIT ROUTINE.                                                             
PS/2 DEVICE HANDLER:                                                      
IF PS/2 Matrix Address                                                    
IF Inbound Transaction                                                    
IF PS/2 Matrix Inbound Queue Empty                                        
        Go to    /***This is a &#34;NACK&#34; response.                           
        COMPLETE   No changes are made to the                             
        TRANSFER   Transfer Descriptor***/                                
Get Data from queue and put in Transfer Descriptor                        
Post good completion transfer descriptor                                  
Go to COMPLETE TRANSFER                                                   
Translate USB Data to PS/2 Data                                           
Post data to PS/2 Matrix outbound queue                                   
Post good completion transfer descriptor                                  
Go to COMPLETE TRANSFER                                                   
IF PS/2 Serial Keyboard Address                                           
IF Inbound Transaction                                                    
IF PS/2 Serial KBD Inbound Queue Empty                                    
Go to            /***This is a &#34;NACK&#34; response.                           
COMPLETE           No changes are made to the                             
TRANSFER           Transfer Descriptor***/                                
Get Data from queue and put in Transfer Descriptor                        
Post good completion transfer descriptor                                  
Go to COMPLETE TRANSFER                                                   
Translate USB KBD Data to PS/2 Data                                       
Post data to PS/2 Serial outbound queue                                   
Post good completion transfer descriptor                                  
Go to COMPLETE TRANSFER                                                   
IF Inbound Transaction                                                    
IF PS/2 Mouse Inbound Queue Empty                                         
Go to COMPLETE   /***This is a &#34;NACK&#34; response.                           
TRANSFER           No changes are made to the                             
                   Transfer Descriptor***/                                
Get Data from queue and put in Transfer Descriptor                        
Post good completion transfer descriptor                                  
Go to COMPLETE TRANSFER                                                   
Translate USB Mouse Data to PS/2 Data                                     
Post data to PS/2 Mouse outbound queue                                    
Post good completion transfer descriptor                                  
Go to COMPLETE TRANSFER                                                   
USB INACTIVE:    /***USB Host is Asleep (or non-                          
                   existent?). Process any PS/2                           
                   Host traffic***/                                       
Get PS/2 Virtual Keyboard Endpoint Descriptor                             
               /***This Endpoint Descriptor                               
                 and any attached Transfer                                
                 Descriptors reside in PS/2 shell                         
                 13***/                                                   
IF any Transfer Descriptors connected to Endpoint Descriptor              
Get next Transfer Descriptor                                              
Perform transfer on USB wire                                              
IF transfer complete                                                      
Put Transfer Descriptor in Done queue                                     
Get PS/2 Virtual mouse End descriptor                                     
               /***This Endpoint Descriptor                               
                 and any attached Transfer                                
                 Descriptors reside in PS/2 shell                         
                 13***/                                                   
IF any Transfer Descriptors connected to Endpoint Descriptor              
Get next Transfer Descriptor                                              
Perform transfer on USB wire                                              
IF transfer complete                                                      
Put Transfer Descriptor in Done queue                                     
IF End of Frame                                                           
Go to DONE       /***This pass is complete***/                            
Go to USB INACTIVE                                                        
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     The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.