Abstract:
A block transfer technique is provided for controlling a data transfer to and/or from a WLAN (Wireless Local Area Network) device connected to a data processing system. The data processing system comprises an operating system independent access controller and a platform specific data block transfer engine. The operating system independent access controller is configured to prepare the platform specific data block transfer engine to perform the data transfer to and/or from the WLAN device.

Description:
This application claims benefit of priority to German patent application 103 55 584.6 filed on Nov. 28, 2003. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to controlling WLAN (Wireless Local Area Network) devices connected to a data processing system, and in particular to a data processing system and method for controlling a data transfer to and/or from such a WLAN device. 
     2. Description of the Related Art 
     A wireless local area network is a flexible data communications system implemented as an extension to or as an alternative for, a wired LAN. Using radio frequency or infrared technology, WLAN systems transmit and receive data over the air, minimizing the need for wired connections. Thus, WLAN systems combine data connectivity with user mobility. 
     Today, most WLAN systems use spread spectrum technology, a wide-band radio frequency technique developed for use in reliable and secure communication systems. The spread spectrum technology is designed to trade-off bandwidth efficiency for reliability, integrity and security. Two types of spread spectrum radio systems are frequently used: frequency hopping and direct sequence systems. 
     The standard defining and governing wireless local area networks that operate in the 2.4 GHz spectrum, is the IEEE 802.11 standard. To allow higher data rate transmissions, the standard was extended to 802.11b that allows data rates of 5.5 and 11 Mbps in the 2.4 GHz spectrum. Further extensions exist. 
     Controlling a WLAN device usually requires some software running on a particular hardware platform. Such software needs to write data from the host to the device and read data from the device to the host. Thus, the software and the WLAN device need to support some transfer mechanism between the host CPU (Central Processing Unit) memory and the WLAN device. One possible transfer mechanism is the DMA (Direct Memory Access) mechanism. 
     In present computer systems, one way of relieving the central microprocessing unit of performing repetitive input/output functions is to avoid interrupts and to realize these functions by means of a DMA controller which is a control unit that enables direct memory access. Before the actual input/output process takes place, the processor initializes the DMA controller by writing initialization data to its registers, and the DMA controller is then able to independently perform data transfers between memory and interface. That is, during the phase where the control and address registers are initialized, the controller acts as slave. However, as soon as the controller receives a transfer request and begins data transmission, the controller independently performs bus cycles, i.e. it acts as master and shares the bus with the processor, for memory access. 
       FIG. 1  depicts a conventional system employing a DMA controller. In this system, the processor  100  is connected to the memory  105 , the DMA controller  110  and a device control unit  120  that controls the peripheral device  125 . Dependent on the mode of operation of the DMA controller  110 , the data transfer between memory  105  and device control unit  120  may be performed directly or indirectly, i.e. by means of a buffer  115 . In the direct transfer mode, the DMA controller  110  requires only one bus cycle per data item by addressing the memory  105  via the address bus and at the same time, addressing the interface data registers via a control line (single address mode). In the indirect transfer mode, the DMA controller  110  first performs a read cycle and stores the read data in the buffer  115 . In a subsequent write cycle, the DMA controller  110  then transfers the buffered data to the respective target unit. Memory and interface are both addressed via the address bus (dual address mode). 
     While the DMA mechanism provides a data transfer technique that has many advantages when controlling devices such as WLAN devices, this technique cannot be used under all circumstances. For instance, situations exist where no bus master DMA is available in the WLAN device that is to be controlled. 
     Thus, the existing techniques suffer from the fact that they are strongly dependent on the used hardware and operating system. For instance, if the hardware and software are designed to use DMA, the architecture is limited to this mechanism. This is likewise true for other memory transfer techniques apart from DMA. Thus, the prior art software is limited to run on the respective specific hardware to use hardware acceleration mechanisms like DMA. 
     SUMMARY OF THE INVENTION 
     A data transfer control technique is provided for controlling the data transfer to and/or from a WLAN device, capable of extending the common way of abstraction of a hardware/software platform an application or device driver is running on, thereby allowing to use the capabilities of the hardware without limiting the software to run on this hardware only. 
     In an embodiment, a data processing system for controlling a data transfer to and/or from a WLAN device is provided where the WLAN device is connected to the data processing system. The data processing system comprises an operating system independent access controller and a platform specific data block transfer engine. The operating system independent access controller is configured to prepare the platform specific data block transfer engine to perform the data transfer to and/or from the WLAN device. 
     In another embodiment, a computer-readable storage medium is provided, storing instructions that when executed by a processor of a data processing system, operate the data processing system to control a data transfer to and/or from a WLAN device that is connected to the data processing system. The computer-readable storage medium comprises instructions to implement an operating system independent access controller, and instructions to implement a platform specific data block transfer engine. The operating system independent access controller is configured to prepare the platform specific data block transfer engine to perform the data transfer to and/or from the WLAN device. 
     In a further embodiment, a method of controlling a data transfer to and/or from a WLAN device is provided where the WLAN device is connected to a data processing system that performs the method. The method comprises operating an operating system independent access controller, and operating a platform specific data block transfer engine. Operating the operating system independent access controller comprises preparing the platform specific data block transfer engine to perform the data transfer to and/or from the WLAN device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are incorporated into and form a part of the specification for the purpose of explaining the principles of the invention. The drawings are not to be construed as limiting the invention to only the illustrated and described examples of how the invention can be made and used. Further features and advantages will become apparent from the following and more particular description of the invention, as illustrated in the accompanying drawings, wherein: 
         FIG. 1  is a block diagram illustrating a conventional system employing a DMA controller; 
         FIG. 2  is a software/hardware arrangement according to an embodiment; and 
         FIG. 3  is a flow chart illustrating the use of the block transfer function in a write transfer example according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrative embodiments of the present invention will be described with reference to the figure drawings wherein like elements and structures are indicated by like reference numbers. 
     Turning now to  FIG. 2  which depicts a block diagram illustrating a software/hardware arrangement according to an embodiment, an OS (Operating System) wrapper  200  is provided that is interconnected to the WLAN device  205 . The OS wrapper  200  is shown to comprise a MAC (Media Access Control) core  210  and a block transfer engine  220 . The MAC core  210  comprises a host memory block or region  215  while the WLAN device  205  comprises a device memory block (or region)  225 . 
     The OS wrapper  200  is a wrapper that may be operating system dependent. In one embodiment, the OS wrapper  200  is part of the operating system. In another embodiment, the OS wrapper  200  is not part of the operating system, but is distributed as separate software product. 
     A wrapper is defined to be software that encases resources. A wrapper may also append code or other software for some purposes. The resources encased in the present embodiment will be described below in more detail, noting that also the block transfer engine  220  may be considered such a resource. 
     The MAC core  210  provides access control functionality. It may be described to relate to the MAC sublayer which is part of the data link layer that supports topology-dependent functions and uses the services of the physical layer to provide services to the logic link control. 
     Before discussing the modes of operation of the architecture shown in  FIG. 2 , some details with respect to the resources are provided that may be used in the embodiments. 
     Generally, communications between processors may be available in the embodiment using messages sent to queues. For attaching data to messages, pointers to the data may be attached. The respective memory may then be needed to be allocated from shared memory. Memory which is intended to be used as a shared resource may be allocated using a predefined parameter. This allows access from all software blocks of the driver. 
     A function call may be available to get a list of hardware resources available. The list may contain two or more elements such as the PCI (Peripheral Component Interconnect) configuration space and a memory mapped register file. A resource identifier may be used for hardware access. The following hardware resource types may be defined: a configuration space, a mapped memory, an I/O (Input/Output) space, and the availability of block transfer functionality. 
     A call of the resource list function may return a pointer to a linked list of resource descriptors. The descriptors hold information about the hardware found. Only the resource type element in a descriptor may be of interest for the MAC core  210 . It provides the necessary information to select the right resource when accessing the WLAN hardware  205 . The pointer to the resource descriptor may be provided with every call to access hardware, allowing the OS wrapper  200  to identify the resource access requested. A pointer may be provided for allowing the OS wrapper  200  to attach data to this structure. The OS wrapper  200  may use this OS dependent data structure to identify the resource. It may be defined in the OS wrapper  200  and not used by the MAC core  210 . 
     Resource access may be available using generic functions. The OS wrapper  200  of the present embodiment is responsible to take care of the type of bus the hardware is connected to. To select the right resource (between memory mapped registers and the PCI configuration space), the resource descriptor corresponding to the selected resource may be passed to read and write functions. 
     The operating system independent MAC core  210  may have the following functions available to access memory mapped registers, I/O space, and the PCI configuration space: write functions for write accesses, with given parameters such as adapter, resource, offset and value; and read functions for read accesses, with given parameters such as adapter, resource, offset and pointer to a value. The write and read access functions may support 8, 16 and 32-bit accesses. As mentioned above, a special resource in the resource list of the present embodiment is the block transfer resource. It allows the operating system independent MAC core  210  to initiate a memory block transfer from the host CPU memory to a location in the device  205  and vice versa. Access to the block transfer resource may be done using the 32-bit read and write access functions. 
     It is to be noted that the block transfer resource  220  does abstract this transfer. It may be used in systems where no bus master DMA from the WLAN device  205  to the host memory and vice versa is available. 
     A block transfer may generally be described to be a process, initiated by a single action, of transferring one or more blocks of data. 
     The location in the device  205  is not necessarily a block of memory. It may be only a register or memory window written with the stream of data representing the block to transfer. The implementation of this block transfer may be a memory copy operation to an interface mapped directly to the host CPU address space, a DMA operation utilizing an available DMA engine on the host, or any other transfer mechanism between the host CPU memory and the WLAN device  205 . 
     In the present embodiment, the block transfer resource  220  provides a number of features including the transfer from host CPU memory to the WLAN device  205 , a transfer from the WLAN device  205  to host CPU memory, and the use of a linked list of memory blocks as source and destination of the transfer. The use of a linked list may, for instance, allow to utilize scatter-gather DMA functionality. 
     The block transfer resource  220  of the present embodiment may provide a number of virtual registers for programming the block transfer state machine. Examples of the virtual registers are one or more host CPU address registers, a device address register, a transfer length register, a command register, and a status register. 
     When writing the host CPU address, the highest 32 bits may be assumed to be zero if they are not written. All other virtual registers not explicitly written may be assumed to be invalid by the state machine. A programming sequence for the state machine may be finished with writing a command using the command register. The status information is valid after sending a command to the block transfer state machine. 
     Examples of block transfer commands are a read command for starting a read block transfer from the WLAN device  205  to the host CPU memory, a write command to start a write block transfer from the host CPU memory to the WLAN device  205 , an abort command to abort the programming sequence, and a “more” command to indicate that more information follows. The use of the commands will be described in more detail below. 
     When the block transfer is finished, an interrupt may either be generated by hardware used or a software interrupt may be used to signal this asynchronous event to the system. When handling this interrupt, the deferred procedure registered by the MAC core  210  may be called. Further, a software interrupt bit in an interrupt status word may be set to signal the source of the interrupt. 
     Turning now to  FIG. 3 , an example for a block transfer is provided. As mentioned above, block transfer may be used in particular when no bus master DMA is available in the WLAN device  205 . In this case, the block transfer function  220  may take care of an efficient transfer of the data between the host memory block  215  and the device memory block  225 . 
     The block transfer engine  220  may therefore be part of the OS wrapper  200  and, due to this, it may be able to make use of platform dependent interfaces or hardware support. An example for this would be the use of a DMA engine available on the host system to do an efficient memory-to-memory transfer. 
     In the block transfer example of  FIG. 3 , a data block is transferred from the host to the WLAN device  205 . In step  300 , the MAC core  210  provides the data in the host memory block  215 . The MAC core  210  then writes the physical address of the host memory block  215  to the block transfer engine  220  in step  305 , using the virtual host address registers. 
     Further, the MAC core  210  writes the relative address of the device memory block  225  to the block transfer engine  220  in step  310 , using the virtual device address register. 
     After that, the MAC core  210  starts the transfer in step  315  by writing a write command to the block transfer engine  220 . The block transfer is then started by the block transfer engine  220 , and the data is copied from the host memory block  215  to the device memory block  225 . 
     Upon finishing the transfer, an interrupt may be generated by real hardware used, or a software interrupt will be generated. The interrupt may be transferred to the MAC core  210  like any other interrupt that is signaled by the WLAN hardware  205 . The interrupt indicates the end of a block transfer operation. The MAC core  210  may then retrieve the status of the transfer by reading the virtual status register of the block transfer engine  220 . 
     In an embodiment, the block transfer engine is also capable of transferring fragmented memory blocks. To be able to cope with fragmented memory on both the host and the device side of the transfer, the block transfer engine  220  supports the “more” data command. If a first address is written and more addresses are to follow, this command is transferred to the block transfer engine  220 . Subsequent addresses are handled as part of a list of blocks to be transferred. Each address may be accompanied by a length indication. With this handling, it does not matter whether none, only one, or both memory blocks  215 ,  225  are fragmented. 
     Given the above description of the various embodiments, a block transfer technique is provided that abstracts data transfer and makes it possible to be used independently from the used hardware or operating system. The transfer may use DMA but is not limited to this mechanism. It is to be noted that the block transfer engine  220  may have a variety of interfaces to the WLAN device  205 , such as busses, host specific DMA engines, shared memory, etc. The described way of abstraction allows to split software in operating system independent parts regardless of the capabilities of the platform this software is running on. 
     It is further to be noted that the embodiments provide other advantages. For instance, the described block transfer technique improves reliability and efficiency. Further, the component parts may be reduced, leading to reduced manufacturing costs. 
     While the invention has been described with respect to the physical embodiments constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications, variations and improvements of the present invention may be made in the light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention. In addition, those areas in which it is believed that those of ordinary skill in the art are familiar, have not been described herein in order to not unnecessarily obscure the invention described herein. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.