Abstract:
A device is presented including a host controller capable of attaching a quantity of queue heads to a frame list. The quantity of queue heads are attached to the frame list before any transaction descriptors where split-isochronous transaction descriptors are supported.

Description:
[0001]    The application is a divisional of U.S. patent application, Ser. No. 09/895,126, filed Jun. 29, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to universal serial bus (USB) environments, and more particularly to an apparatus to improve performance of an enhanced host controller interface (EHCI) for USB devices.  
           [0004]    2. Description of the Related Art  
           [0005]    In many of today&#39;s processors and systems, such as personal computer (PC) systems, there exist USB ports for connecting various USB devices. Many USB devices are frequently used by PC users. For example, USB devices may be printers, compact disc read-only memory (CD-ROM) drives, CD-ROM writer (CDRW) drives, digital versatile disc (DVD) drives, cameras, pointing devices (e.g., computer mouse), keyboards, joy-sticks, hard-drives, speakers, etc.  
           [0006]    Different standards of USB technology have different bandwidths. For example, Universal Serial Bus Specification, revision 1.1, Sep. 23, 1998 (USB 1.1) devices are capable of operating at 12 Mbits/second (Mbps), and Universal Serial Bus Specification, revision 2.0, Apr. 27, 2000 (USB 2.0; also known as high-speed USB) devices are capable of operating at 480 Mbps. USB 2.0 defines a multiple speed-signaling environment where a single high-speed bus may support one or more USB 1.1 classic busses through a USB 2.0 hub (Transaction Translator). In this environment, system software (the Host Controller Driver) must allocate and manage the bandwidth of USB 1.1 classic busses.  
           [0007]    The Enhanced Host Controller Interface (EHCI) specification for a Universal Serial Bus, revision 0.95, Nov. 10, 2000, describes the register-level interface for a Host Controller (HC) for USB 2.0. In the USB EHCI specification, a single data structure known as the interrupt queue head is defined. The interrupt queue head represents and manages traffic to interrupt endpoints behind a given transaction translator (TT). A timed event, known as period promotion, may consume up to 255× the typical bandwidth of interrupt queue heads. Therefore, period promotion consumes a large portion of bandwidth in a USB 2.0 system. Thus, period promotion is very costly in a USB 2.0 system in terms of bandwidth usage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.  
         [0009]    [0009]FIG. 1 illustrates a Universal Serial Bus (USB) system.  
         [0010]    [0010]FIG. 2 illustrates a USB host controller.  
         [0011]    [0011]FIG. 3 illustrates an enhanced host controller interface (EHCI).  
         [0012]    [0012]FIG. 4 illustrates a queue head structure layout.  
         [0013]    [0013]FIG. 5 illustrates a periodic schedule.  
         [0014]    [0014]FIG. 6A-B illustrates a structure of a isochronous transfer descriptor (iTD).  
         [0015]    [0015]FIG. 7 illustrates a structure of a split-transaction isochronous transfer descriptor (siTD).  
         [0016]    [0016]FIG. 8 illustrates an embodiment of the invention having queue heads coupled directly to a frame list.  
         [0017]    [0017]FIG. 9 illustrates a block diagram of an embodiment of the invention having queue heads coupled directly to a frame list during initialization.  
         [0018]    [0018]FIG. 10 illustrates a block diagram of an embodiment of the invention having queue heads coupled directly to a frame list after initialization. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    The invention generally relates to an apparatus and method to improve bandwidth usage of Universal Serial Bus (USB) devices. Referring to the figures, exemplary embodiments of the invention will now be described. The exemplary embodiments are provided to illustrate the invention and should not be construed as limiting the scope of the invention.  
         [0020]    A typical USB host system is composed of a number of hardware and software layers. FIG. 1 illustrates a block diagram of typical building block layers in a USB 2.0 system. System  100  is comprised of client driver software  110 , universal bus driver (USBD)  120 , companion host controller (HC) driver  130 , companion HC  140 , enhanced host controller driver (EHCD)  150 , universal host controller (UHC)  160  and USB device  170 . In system  100 , system software consists of client driver software  110 , USBD  120 , companion HC driver  130 , and EHCD  150 . In system  100  the hardware comprises companion HC  140 , UHC  160 , and USB device  170 .  
         [0021]    Client driver software  110  typically executes on the host PC corresponding to a particular USB device. Client driver software  110  is typically part of the operating system (OS) or may be provided with a USB device. USBD  120  is a system bus driver that abstracts the details of the particular HC driver for a particular OS. Companion HC driver  130  is typically a UHC interface (UHCI) driver or an open HCI (OHCI) driver for USB. The HC driver provides a software layer between specific HC hardware and the USBD. Companion HC  140 , is typically UHCI or OHCI standards. Companion HC  140  is the specific hardware implementation of the HC. There is one HC specification for USB 2.0 functionality, and two specifications for full-and low-speed HCs.  
         [0022]    [0022]FIG. 2 illustrates typical USB 2.0 HC  200 . A USB 2.0 HC includes one high-speed mode HC and zero (0) or more USB 1.1 HCs. USB 2.0 HC  200  comprises companion USB HC and high-speed mode (enhanced interface) HC  160 . Companion HC  140  comprises HC control logic/data buffering  210  (including port  1  through port N). High-speed mode HC  160  comprises enhanced HC control logic/enhanced data buffering  220  (including port  1  through port N). Also included in USB 2.0 HC  200  is port routing logic  230  (including port  1  through port N).  
         [0023]    [0023]FIG. 3 illustrates the general architecture of enhanced host controller interface (EHCI)  300 . EHCI  300  comprises three interface spaces: peripheral component interconnect (PCI) configuration  310 , register  320 , and schedule interface  330 . PCI configuration  310  includes PCI registers used for system component enumeration and PCI power management. PCI configuration registers in PCI configuration  310  comprise PCI class code  311 , USB base address  312 , and PCI power management interface  313 . Register  320  comprises memory based input/output (I/O) registers. Memory based I/O registers are comprised of capability registers  321  and operational registers  322 . Register  320  must be implemented as memory-mapped I/O. Schedule interface  330  is typically memory allocated and managed by the HC driver for the periodic and asynchronous schedules. EHCI  300  allows software to enable or disable each schedule.  
         [0024]    [0024]FIG. 4 illustrates a typical structure layout of a queue head. Queue head horizontal link pointer (QHLP)  410  comprises four fields. QHLP field  411  contains the address of the next data object to be processed in the horizontal list and corresponds to memory address signals  31 : 5 , respectively. Field  412  is reserved, and bits  4 : 3  must be written as Os. Field  413  comprising bits  2 : 1 , indicates to the hardware whether the item referenced by the link pointer is a isochronous transaction descriptor (iTD), split transaction isochronous transaction descriptor (siTD) or a queue head. Field  413  allows the HC to perform the proper type of processing on the item after it is fetched. Field  14 , bit  0 , is the terminate field. If the queue head is in the context of the periodic list, a set (1) bit in field  414  indicates to the HC that this is the end of the periodic list. This bit, however, is ignored by the HC when the queue head is in the asynchronous schedule.  
         [0025]    Field  420  illustrates queue head DWord 1 , and field  430  illustrates end point characteristics comprising queue head DWord 2 . Field  421  is the not acknowledged or negative acknowledged (Nak) count re-load field. Field  421  contains a value, which is used by the HC to reload Nak counter field. Field  433  illustrates a control end-point flag. Field  423  represents the maximum packet length. The maximum packet length directly corresponds to the maximum packet size of the associated endpoint. The maximum value of field  423  is 0×400 ( 1024 ).  
         [0026]    Field  424  illustrates head of reclamation list flag. Field  424  is set by system software to mark a queue head as being the head of the reclamation list. Field  425  illustrates data toggle control. Field  425  specifies where the HC should get the initial data toggle on an overlay transition. Field  426  illustrates endpoint speed. Field  426  is the speed of the associated endpoint. Field  427  illustrates the endpoint number. Field  427  selects the particular endpoint number on the device serving as the data source or sink. Field  428  is a reserved bit. Field  429  illustrates the device address. Field  429  selects the specific device serving as the data source or sink.  
         [0027]    Field  431  illustrates the high-bandwidth pipe multiplier. Field  431  is a multiplier used to key the HC as the number of successive packets the HC may submit to the endpoint in the current execution. The HC makes the simplified assumption that software properly initializes this field. Field  432  illustrates the port number. Field  432  is ignored by the HC unless field  426  indicates a full-speed or low-speed device. The value is the port number identifier on the USB 2.0 hub, below which the full- or low-speed device associated with this endpoint is attached. This information is used in the split-transaction protocol. Field  433  illustrates the hub address. Field  433  is ignored by the HC unless field  426  indicates a full- or low-speed device. The value is the USB device address of the USB 2.0 hub below which the full- or low-speed device associated with this endpoint is attached.  
         [0028]    Field  434  illustrates the split-completion mask. Field  434  is ignored by the HC unless field  426  indicates the device is a low- or full-speed device and this queue head is in the periodic list. Field  434  is used to determine during which micro-frames the HC should execute a complete-split transaction. When the criteria for using this field are met, a zero value in this field has undefined behavior. Field  435  illustrates the interrupt schedule mask. Field  435  is used for all endpoint speeds. When the queue head is on the asynchronous schedule, software should set this field to a zero. A non-zero value in this field indicates an interrupt endpoint.  
         [0029]    Field  440  illustrates the current queue transaction descriptor link pointer. Field  440  contains the address of the current transaction being processed in this queue and corresponds to memory address signals  31 : 5 , respectively. Field  441  is reserved for future use. Field  442  illustrates the next qTD pointer. Field  443  illustrates the alternate next qTD pointer. Fields  450  through  454  illustrate buffer pointer pages  0 - 4 , respectively.  
         [0030]    [0030]FIG. 5 illustrates an example of a periodic schedule. The periodic schedule is used to manage all isochronous and interrupt transfer streams. The base of the periodic schedule is periodic frame list  510 . Software links schedule data structures to periodic frame list  510  to produce a graph of scheduled data structures. The graph represents the appropriate sequence of transactions on the USB. Periodic schedule  500  also illustrates isochronous transfers, (using iTDs and siTDs) with a period of one, linked directly to periodic frame list  510 . Interrupt transfers (are managed with queue heads) and isochronous streams, with periods other than one, are linked following the period-one iTD/siTDs. Interrupt queue heads  530  are linked into periodic frame list  510  ordered by poll rate. Longer poll rates are linked first (e.g. closest to periodic frame list  510 ), followed by shorter poll rates, with queue heads with a poll rate of one (1), on the very end.  
         [0031]    [0031]FIG. 6A-B illustrates the structure of an iTD. The structure illustrated in FIG. 6A-B is used only for high-speed isochronous endpoints. All other transfer types should use queue structures. Link pointer  605  is a pointer to the next schedule data structure (iTD, siTD, or queue head. Field  606  is reserved. Field  606  indicates to the HC whether the item referenced is a iTD, siTD, or a queue head. By informing the HC of the type of data structure, the HC can perform the proper type of processing on the item after it is fetched. Field  611  records the status of the transaction executed by the HC for the particular slot. Field  612  is the transaction length (i.e. number of data bytes) the HC will send during the transaction. Field  613  is the interrupt on complete (IOC) bit. If the IOC bit is set to a one (“1”), it specifies that when the transaction completes, the HC should issue an interrupt at the next interrupt threshold. Field  614  is the page select.  
         [0032]    The page select field  614  are set by software to indicate which of the buffer page pointers the offset field  615  in the particular slot should be concatenated to produce the beginning memory address for the particular transaction. Offset field  615  is a value that is an offset, expressed in bytes, from the beginning of a buffer. Offset field  615  is concatenated onto the buffer page pointer indicated in the page select field  614  to produce the beginning buffer address for the particular transaction. Buffer page pointer list  620  provides 7 page pointers to support the expression of eight (“8”) isochronous transfers. The seven pointers allow for three (“3”) transactions *  1024  (maximum packet size) * eight (“8”) transaction records (24,576 bytes) to be moved with this data structure, regardless of the alignment offset of the first page.  
         [0033]    [0033]FIG. 7 illustrates a siTD. All full-speed isochronous transfers through transaction translators (TTs) are managed using the siTD data structure. Field  710  is the next link pointer. Field  710  contains the address of the next data object to be processed in the periodic list and corresponds to memory address signals  31 : 5 , respectively. Field  715  is the QH/(s)iTD select. Field  715  indicates to the HC whether the item referenced is a iTD/siTD or QH. Field  716  is the terminate field. Field  717  is reserved.  
         [0034]    Field  720  is the direction, that is input or output. Field  720  encodes whether the full-speed transaction is IN or OUT. Field  721  is the port number of the recipient TT. Field  722  is reserved. Field  723  is the device address of the TT&#39;s hub. Field  724  is reserved. Field  725  is a four-bit field that selects the particular endpoint number on the device serving as the data source or sink. Field  726  is reserved. Field  727  selects the specific device serving as the data source or sink.  
         [0035]    Field  730  is reserved. Field  731 , the split completion mask, and field  732 , the split start mask, are used to determine during which micro-frames the HC should execute complete-split transactions. Field  740  is the interrupt on complete field. When field  740  is set to a one (1), the HC will assert a hardware interrupt at the next interrupt threshold when the HC determines that the split transaction has completed. When field  740  is set to a zero (0), the HC will not assert an interrupt when the HC determines that the split transaction has completed. Field  741  is sued to indicate which data page pointer should be concatenated with field  751  (discussed below) to construct a data buffer pointer. Field  742  is reserved. Field  743  is initialized to the total number of bytes expected in the transfer (maximum value is 1023). Field  743  is used by the HC to record which split-completes have been executed. Field  744  records the status of the transaction executed by the HC for this slot.  
         [0036]    Field  750  is the buffer pointer list for page  0 . Field  751  is the current offset field. In field  751 , the twelve least significant bits of the Page  0  pointer is the current byte offset for the current page pointer. Field  760  is the buffer pointer list for Page  1 . Field  761  is reserved. Field  762  is the transaction position. Field  762  is used with field  763  to determine whether to send all, first, middle, or last with each outbound transaction payload. Field  763  is initialized by software with the number of OUT start-splits the transfer requires. Field  770  is the siTD back pointer. Field  770  is a physical memory pointer to an siTD. Field  771  is reserved. Field  772  is a terminate field.  
         [0037]    [0037]FIG. 8 illustrates a resulting frame list of an embodiment of the invention that couples interrupt queue heads directly to the HC frame list, but before any siTDs in a USB 2.0 system. Note that embodiments of the invention can be used with future USB systems where queue heads are typically not directly coupled to the frame list before siTDs. One should note that the FIG. 8 is an example with only eight (“8”) elements in the frame list, but the invention is not limited to eight (“8”) elements. In this embodiment of the invention, interrupt queue heads  810  are not part of the standard interrupt tree. An example of a standard interrupt tree can be seen in FIG. 5.  0036  In FIG. 5, it can be seen that iTDs  520  are directly coupled to periodic frame list  510 . In FIG. 5, interrupt queue heads  530  are part of the interrupt tree. In this embodiment of the invention, by coupling interrupt queue heads  810  directly to frame list  820 , where the coupled interrupt queue heads are coupled before split iTDs  830 , interrupt queue heads  810  are not subject to period promotion. In this embodiment of the invention, the HC Driver maximizes the number of devices using periodic (isochronous and interrupt) endpoints that can be connected to a TT. By preventing period promotion, this embodiment of the invention uses less of the available bandwidth on a USB 2.0 system.  
         [0038]    [0038]FIG. 9 illustrates a block diagram of an embodiment of the invention having process  900  that couples queue heads directly to a frame list during initialization. Block  910  determines whether a queue head max packet size is less than or equal to a predetermined size (such as one (“1”) byte) and that the period is greater or equal to a predetermined schedule window (dependent on number of data structures, such as iTD and siTD). In one embodiment of the invention, block  910  also determines whether the queue head is full speed or not. Note that the queue heads can be of any sufficiently small maximum packet size that allows sufficient bandwidth to remain for a maximum sized (1023 bytes per frame) full speed isochronous transfer.  
         [0039]    If block  910  determines that a queue head max packet size is not equal to or less than a predetermined size and/or that the period is not greater or equal to a predetermined schedule window, then process  900  continues with block  950 . Block  950  places the queue head in the interrupt tree. Process  900  then continues to block  940 . Process  900  continues with block  940  that determines whether initialization is complete or not (i.e., all queue heads are processed). If block  940  determines that all queue heads are not processed, then process  900  continues with block  910 . If block  940  determines that all queue heads are processed, process  900  completes.  
         [0040]    If block  910  determines that a queue head max packet size is less than or equal to a predetermined size and that the period is greater or equal to a predetermined schedule window, then process  900  continues with block  920 . Block  920  initializes the next pointer in the queue head to contain the contents of the current entry in the frame list. Process  900  continues with block  930  that replaces the current entry in the frame list with a pointer to a new queue head. Process  900  then continues with block  940 .  
         [0041]    [0041]FIG. 10 illustrates a block diagram of an embodiment of the invention having process  1000  that couples queue heads directly to a frame list after initialization of the interrupt tree. Block  1010  determines whether a queue head maximum packet size is less than or equal to a predetermined size (such as one (“1”) byte) and that the period is greater or equal to a predetermined schedule window (dependent on number of data structures, such as iTD and siTD). In one embodiment of the invention, block  1010  also determines whether the queue head is full speed or not. Note that the queue heads can be of any sufficiently small maximum packet size that allows sufficient bandwidth to remain for a maximum sized ( 1023  bytes per frame) full speed isochronous transfer.  
         [0042]    If block  1010  determines that a queue head max packet size is not less than or equal to a predetermined size and/or that the period is not greater or equal to a predetermined schedule window, then process  1000  continues with block  1050 . Block  1050  determines whether more queue heads exist in the interrupt tree. If block  1050  determines that more queue heads exist in the interrupt tree, process  1000  continues with block  1010 . If block  1050  determines that there are not any more queue heads in the interrupt tree, process  1000  is complete.  
         [0043]    If block  1010  determines that a queue head max packet size is less than or equal to a predetermined size and that the period is greater or equal to a predetermined schedule window, then process  1000  continues with block  1020 . Block  1020  initializes the next pointer in the queue head to contain the contents of the current entry (queue head, iTD, siTD) in the frame list. Process  1000  continues with block  1030  that replaces the next pointer of the queue head to point to the current entry in the frame list. Process  1000  then continues with block  1040 . Block  1040  replaces the current entry in the frame list with a pointer to a new queue head. Process  1000  then continues with block  1050 .  
         [0044]    The above embodiments can also be stored on a device or machine-readable medium and be read by a machine to perform instructions. The machine-readable medium includes any mechanism that provides (i.e., stores and/or transmits) information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). The device or machine-readable medium may include a solid state memory device and/or a rotating magnetic or optical disk. The device or machine-readable medium may be distributed when partitions of instructions have been separated into different machines, such as across an interconnection of computers.  
         [0045]    While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.