Abstract:
A method and apparatus for dynamically assigning and enabling a unique functional address for a Universal Serial Bus device. A host assigns the unique functional address during a control transaction. The Universal Serial Bus device disables the default address and enables the unique functional address during a status stage of the control transaction to avoid an error window.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This apparatus and method relates to initializing a Universal Serial Bus device and, in particular, to assigning a unique functional address to a Universal Serial Bus device. 
     2. Description of the Related Art 
     Universal Serial Bus (USB) is a standard peripheral interface for attaching personal computers to a wide variety of devices: e.g., digital telephone lines, monitors, modems, mice, printers, scanners, game controllers, keyboards, and other peripherals. A USB thus replaces existing interfaces such as the RS-232C serial ports, parallel ports, PS/2 interface and game/MIDI ports. 
     In accordance with USB, all attached devices connect to a personal computer through a single connector type using a tiered-star topology. A host personal computer includes a single USB controller. The host controller provides the interface between the USB network and the host personal computer. The host controller controls all accesses to USB resources and monitors the bus topology. A USB hub provides USB attachment points for USB devices. 
     An example of the tiered-star topology of a USB network is shown in FIG.  1 . Host PC  100  is a typical personal computer having a USB port connection via host controller  102 . Host controller  102  connects directly to hub  110 . Compound device  120 , hub  130 , and device  140  connect to the host controller  102  through hub  110 . Devices  132  and  134  connect to the host controller  102  through hub  130  and through hub  110 . 
     Compound device  120  includes devices  124 ,  126  and hub  122 . Hub  122  of compound device  120  connects to the host controller through hub  110 . Devices  124  and  126  of compound device  120  connect to the host controller  102  through hub  122  and through hub  110 . A practical example of a compound device would be an integrated printer and fax. The printer could be device  124 , and the fax could be device  126 . 
     The tiered-star topography illustrated in FIG. 1 allows data to be transmitted into and out of the host PC  100  to the various devices. When data is transmitted from the host to a device it is transmitted downstream through the interconnecting hubs. When data is transmitted from a device to the host it is transmitted upstream through the interconnecting hubs. 
     USB hubs and devices may be connected and disconnected without completely re-starting the USB network. Upon connection of a device or hub to an upstream hub the upstream hub will notify the host controller of a change in status. Following USB protocol, the host controller will enable the port of the hub to which the device is connected. The host controller will then assign a unique functional address to each device. Ports are enabled one at a time as the host controller  102  assigns unique functional addresses. Upon connection of a compound device, the host controller assigns a unique functional address to each device contained within the compound device. Returning to FIG. 1, devices  124 ,  126 ,  132 ,  134 , and  140  in addition to hubs  110 ,  122 , and  130  will each be assigned a unique functional address upon attachment to the USB network. 
     Devices  124 ,  126 ,  132 ,  134 , and  140  in addition to hubs  110 ,  122 , and  130  will each respond to a default address of 00h until they are assigned the unique functional address. Each of the devices include registers which may be read by the host controller. The registers include a default (DEF) bit, a functional address enable (AE) bit, and a functional address register (FAR). The default bit indicates whether the device will respond to the default address. If it is set, the device will respond to the default address, if it is cleared it will not. The functional address enable bit indicates whether the device will respond to the address stored in the functional address register. If it is set, the device will respond to the address stored in the functional address register, if it is cleared it will not. 
     All of the devices  124 ,  126 ,  132 ,  134 , and  140  attach to the host controller  102  through at least one hub. Each hub has one upstream port and at least one downstream port. Upon attachment or removal of a device on a downstream port, a hub will notify the host controller of a change in status. The host controller then queries the hub to determine the change in status on the hub&#39;s ports. 
     Upon attachment of a device to one of a hub&#39;s downstream ports, the above procedure is followed to notify the host controller of the attachment of a new device. A hub&#39;s downstream ports are by default disabled until the host controller enables them. Consequently, the host controller will enable the port. 
     Upon removal of a device from one of a hub&#39;s downstream ports, the hub automatically disables the appropriate port and notifies the host of the change. The host controller updates the topography status to reflect the change. 
     The process of activating a newly attached device will now be described in greater detail. When a device is attached to a downstream port of a hub, the hub will notify the host controller of the change in status via a status change pipe. The host controller queries the hub to determine which of the downstream ports have experienced a connection. The host controller then issues a port enable and reset command to the appropriate port. The enable command enables the port and provides power to the device. The reset command resets all of the devices registers and state information. The device will respond to a default address and is accessible over a default pipe. The host controller then reads a device descriptor to determine the characteristics of the default pipe. The host then assigns a unique functional address to the device thereby moving the device to the addressed state. The host then reads the configuration information from the device, and writes a configuration value to the device. This moves the device to the configured state. 
     The transaction for assigning a unique functional address during the above described activation process will now be described in greater detail. These transactions are first described generally, then are described as applied to assigning a unique functional address. 
     The USB specification defines a control transfer protocol for use in configuring a device. A control transfer is composed of a setup transaction which moves request information from the host to the device, optional data transactions which send data in the direction indicated by the setup transaction, and a status transaction which returns status information from the device to the host. 
     The occurrence of an IN or OUT data transaction in the control transaction provide three possible transaction sequences: a control write sequence, a control read sequence, and a control no-data sequence. Each of these will now be described in greater detail. 
     Turning to FIG. 4A, a control write sequence is shown. The control write sequence includes three stages: a setup stage, a data stage and a status stage. The setup stage consists of a SETUP transaction  410  having a DATA 0  PID. The SETUP transaction  410  specifies that an OUT data stage will follow. The data stage consists of an OUT transaction  412  having a DATA 1  PID. The OUT transaction  412  is followed by an OUT transaction  414  having a DATA 0  PID. This transaction is followed by as many transactions as are required to transmit the necessary data from the host. This will depend both upon the size of the data in the host and the size of the transmitted packets. The DATA PID alternates between 1 and 0 for the OUT transactions used in the data stage. The final OUT transaction  416  ends the data stage. The status stage consists of a single IN transaction  418  having a DATA 1  PID. 
     Turning to FIG. 4B, a control read sequence is shown. The control data IN sequence includes three stages: a setup stage, a data stage and a status stage. The setup stage consists of a SETUP transaction  420  having a DATA 0  PID. The SETUP transaction  420  specifies that an IN data stage will follow. The data stage consists of an IN transaction  422  having a DATA 1  PID. The IN transaction  422  is followed by an IN transaction  424  having a DATA 0  PID. This token is followed by as many transaction as are required to transmit the necessary data from the device. This will depend both upon the size of the data in the device and the size of the transmitted packets. The DATA PID alternates between 1 and 0 for the IN transactions used in the data stage. The final IN transaction  426  ends the data stage. The status stage consists of a single IN transaction  428  having a DATA 1  PID. 
     Turning to FIG. 4C, a control no-data sequence is shown. The control no-data sequence includes two stages: a setup stage and a status stage. The setup stage consists of a SETUP transaction  420  having a DATA 0  PID. The status stage consists of a single OUT transaction  428  having a DATA 1  PID. 
     A flow chart illustrating a setup transaction is shown in FIG.  3 . The transaction begins with SETUP token  310  sent from the host. A setup transaction always includes a DATA 0  PID for the data field. The device then responds by sending an ACK handshake to complete the SETUP transaction. 
     A flow chart illustrating an IN transaction is shown in FIG.  5 . The IN transaction begins with an IN token  510  which is sent from the host to the device. The device should then respond with the appropriate DATA packet  512  (either a DATA 0  or a DATA 1  packet). If, however, the device is temporarily unable to return a DATA packet, it will instead return NAK handshake  514 . If the device is unable to return a DATA packet and will require host intervention to recover, it will return a STALL handshake  516 . Returning to DATA packet  512 , the host will respond with an ACK handshake  518  upon receipt of this packet. 
     A flow chart illustrating an OUT transaction is shown in FIG.  6 . The OUT transaction begins with an OUT token  610  which is sent from the host to the device. The host then sends the appropriate DATA packet  612  (either a DATA 0  or a DATA 1  packet). If the device receives DATA packet  612  without errors and is ready to receive another packet, it returns ACK handshake  614 . If the device receives DATA packet  612  without errors but needs the host to resend the packet, it returns NAK handshake  616 . The NAK handshake is used when a DATA packet&#39;s intended function is in a state which temporarily prevents it from receiving the DATA packet. If the device receives the DATA packet  612  but is in a stall condition, it returns a STALL handshake to indicate that the host should not attempt to resend the packet. If the data packet  612  is received with a CRC or bit stuffing error, no handshake is returned. 
     Upon connection of a device to a host port, the host will use a control write transfer to assign a unique functional address. As described above, a successful control write transfer consists of a SETUP transaction, at least one OUT transactions, and an IN transaction. The SETUP transaction is addressed to the default address. The OUT transaction(s) include the unique functional address for the device. The IN transaction consists of the IN token from the host, a zero-length DATA 1  packet from the device to the host, and an ACK handshake from the host to the device. 
     To enable the functional address, each of the devices  124 ,  126 ,  132 ,  134 , and  140  and hubs  110 ,  122  and  130  in turn sets a functional address bit. After completion of the OUT transactions of a setup control transfer for assigning a unique functional address, a device has received the unique functional address. This address is loaded into the device&#39;s functional address register, and the address enable bit is set. The host then sends an IN token to begin the status stage of a setup control transfer. The status stage is used to confirm completion of the control transfer. Having loaded a unique functional address, the default address bit is cleared upon receipt of the following IN token. The device simultaneously sends a DATA 1  packet to the host. The DATA 1  packet indicates that the endpoint is now in a condition to be addressed by the host. If the device is experiencing temporary delays, it can transmit instead a NAK handshake packet. Alternatively, if the device is experiencing an error condition, it can transmit a STALL to indicate that the host should not attempt to resend data. 
     On many USB networks, the transmission of data is not completely errorless. Occasionally data transmissions are corrupted, and any of the above described transmissions may be corrupted. 
     For example, the zero-length DATA 1  packet sent by the device during the status stage may be corrupted or simply lost on it&#39;s way through the USB network to the host. During the window of time after such a loss, the host will not send the appropriate ACK because it has not properly received the DATA 1  packet. 
     Instead, the host may attempt to restart the setup control transfer by sending a SETUP token or an IN token to the default address of the device. As the device has cleared the default address bit, it will no longer respond to this token. 
     Additionally, the host may have already enabled another hub port connected to an as yet unconfigured device. Although the SETUP token is not directed to the unconfigured device, it will respond. Such a response may cause further errors particularly in the hosts monitoring to the bus topography. 
     Accordingly, methods and apparatus for avoiding the potential errors resulting from the corruption or loss of data transmissions during the setup control transfer are desired. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide for robust assignment of a functional address using a setup control transfer. 
     It is a further object of the invention to complete a functional address assignment even where some of the data transmitted during a setup control transfer may be lost or corrupted. 
     It is an advantage of the invention to avoid the undefined window of time following the loss or corruption of a status stage DATA 1  packet. 
     It is a feature of one aspect of the invention to enable a unique functional address upon receipt of a valid ACK after the status phase or on a SETUP token for another device. 
     It is a feature of the invention to accept address assignment in compound devices having multiple functional addresses. 
     According to one aspect of the invention a USB device has a default address, and a default address enable bit wherein the default address enable bit enables the use of the default address. The device receives an IN token from a host; sends a DATA 1  packet to the host; receives an ACK from the host; and clears the default address bit only after receiving the ACK. 
     According to another aspect of the invention a USB device has a default address, and a default address enable bit wherein the default address enable bit enables the use of the default address. The device receives an IN token from a host; sends a zero-length DATA 1  packet to the host; receives a SETUP packet from the host; and clears the default address enable bit upon receipt of the SETUP packet. 
     According to another aspect of the invention a USB network includes a host and a plurality of devices, wherein the devices are of the type having a default address and a default address enable bit, and further wherein the default address enable bit enables the use of the default address. A method for operating the USB network sends an IN token from the host to a first device; receives the IN token by the first device; sends a DATA 1  packet from the first device to the host; receives the DATA 1  packet by the host; sends an ACK from the host to the first device; sends a SETUP token from the host to a second device; and clears the default address bit of the first device upon receipt of one of the ACK or the SETUP token. 
     According to another aspect of the invention, a USB device utilizes a default address enable bit, wherein when the default address enable bit is set the USB device responds to a default address and when the default address bit is cleared the USB device does not respond to the default address, and further wherein the default address enable bit is cleared upon receipt of an ACK handshake during a status stage of a control transfer. 
     These and other objects, features, and advantages will become apparent when considered with reference to the following description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a Universal Serial Bus network. 
     FIG. 2 is a block diagram of one preferred embodiment of an interface module for a Universal Serial Bus device in accordance with the present invention. 
     FIG. 3 is a flow chart showing data flow over a USB network during a SETUP transaction. 
     FIG. 4A is a flow chart showing data flow over a USB network during a control write transfer. 
     FIG. 4B is a flow chart showing data flow over a USB network during a control read transfer. 
     FIG. 4C is a flow chart showing data flow over a USB network during a control no-data transfer. 
     FIG. 5 is a flow chart showing data flow over a USB network during an IN transaction. 
     FIG. 6 is a flow chart showing data flow over a USB network during an OUT transaction. 
     FIG. 7 is a functional address register for a USB device according to one preferred embodiment of the invention. 
     FIG. 8 is a device control register for a USB device according to one preferred embodiment of the invention. 
     FIG. 9 is a flow chart showing the assignment of functional addresses according to one preferred embodiment of the invention. 
     FIG. 10 is a flow chart showing a control transaction which assigns and enables a unique functional address according to one preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference now to FIG. 2, a USB device  210  in accordance with the invention is described. The preferred embodiment of the device conforms to Revision 1.0 of the USB Specification while providing a number of advantages over conventional USB devices. The USB device  210  includes a USB interface module  220 , a register set  214 , a RAM  212 , and a BIU  216 . 
     The interface module  220  connects to a USB network to send and receive data. The interface module  200  also connects to register set  214 , RAM  212 , and BIU  216  via a core bus  218 . The core bus  218  allows the interface module  200  to access the register set  214  and the RAM  212 . 
     The register set  214  includes a functional address register and a device control register. Turning to FIG. 7, one preferred embodiment of a functional address register  710  is shown. The functional address register  710  is 32 bits long and provides space for four functional addresses. 
     Bits  0 - 6  of the functional address register  710  provide space for a first functional address designated FA 0 . Bit  7  provides space for a first address enable bit designated AE 0 . Bits  8 - 14  of the functional address register  710  provide space for a second functional address designated FA 1 . Bit  15  provides space for a second address enable bit designated AE 1 . Bits  16 - 22  of the functional address register  710  provide space for a third functional address designated FA 2 . Bit  23  provides space for a third address enable bit designated AE 2 . Bits  24 - 30  of the functional address register  710  provide space for a fourth functional address designated FA 3 . Bit  31  provides space for a first address enable bit designated AE 3 . 
     The four functional addresses, FA 0 , FA 1 , FA 2 , and FA 3  along with the four address enable bits, AE 0 , AE 1 , AE 2 , and AE 3  are provided to support the operation of a compound device having up to four address. After a functional address has been assigned, the related address enable bit may be set to enable use of the functional address. 
     Turning to FIG. 8, one preferred embodiment of a device control register  810  is shown. The device control register  810  is  16  bits long. 
     Bit  4  provides space for a first default address enable bit, DEF 0 , which relates to the first functional address, FA 0 . Bit  5  provides space for a second default address enable bit, DEF 1 , which relates to the second functional address, FA 1 . Bit  6  provides space for a third default address enable bit, DEF 2 , which relates to the third functional address, FA 2 . Bit  7  provides space for a fourth default address enable bit, DEF 3 , which relates to the fourth functional address, FA 3 . 
     The default address enable bits are used to indicate whether the device will respond to the default address. When these bits are set the device will respond to the default address, when they are cleared it will not. 
     After a functional address has been assigned, the related functional address bit is set to indicate that the address is valied. After this, the related default address bit will be cleared and the device will no longer respond to the default address and will instead respond to the functional address. 
     Turning to FIG. 9, the assignment of functional addresses will now be described in detail. Starting at block  910 , a USB device having four possible functional addresses is connected to a USB device. At block  912 , the USB device tests for receipt of a SETUP token indicating a control transfer for assigning a functional address. Upon receipt of such a token, at block  914 , the USB device performs the control transfer, assigns FA 0 , and sets AE 0 . DEF 0  is cleared by the device the next time an ACK is received in response to an IN token. If no ACK is received within a timeout period, if the next token is a SETUP, this will also cause the DEF 0  bit to be reset. 
     At block  916 , the USB device again tests for receipt of a SETUP token indicating a control transfer for assigning a functional address. Upon receipt of such a token, at block  918 , the USB device performs the control transfer, assigns FA 1 , and sets AE 1 . DEF 1  is cleared as described above. At block  920 , the USB device again tests for receipt of a setup token indicating a control transfer for assigning a functional address. Upon receipt of such a token, at block  922 , the USB device performs the control transfer, assigns FA 2 , and sets AE 2 . DEF 2  is cleared as described above. At block  924 , the USB device again tests for receipt of a setup token indicating a control transfer for assigning a functional address. Upon receipt of such a token, at block  926 , the USB device performs the control transfer, assigns FA 3 , and sets AE 3 . DEF 3  is cleared as described above. This completes assignment of the four functional addresses. 
     Depending upon how many functional addresses have been assigned, the device  210  may respond to one or more assigned functional address and a default address. 
     Preferred embodiments of the device activate the functional addresses depending upon the particular needs of the implementation. Consequently, one to four functional addresses may be assigned. 
     The enablement of a functional address according to one preferred embodiment of the invention is shown in FIG.  10 . At start block  1010  a USB device is connected to a USB network and tests for a SETUP token indicating a control transfer for assigning a functional address. Upon receipt of such a token the device proceeds to block  1012  where it completes a setup transaction. Upon completion of the setup transaction, the device proceeds to block  1014  to receive an OUT token. The device then proceeds to complete one or more OUT transactions. These transactions contain a unique functional address which is stored in the appropriate functional address register. Upon completion of the data stage at block  1014 , the device tests for an IN token. Upon receipt of the IN token, the device proceeds to block  1018  where it sends a zero-length DATA 1  packet. After sending the DATA 1  packet, the device proceeds to block  1020 , where it tests for receipt of either an ACK handshake or else another SETUP token. Upon receipt of either, the device proceeds to block  1022  where it clears the related DEF bit. This enables use of the unique functional address and disables use of the related default address. 
     If the device does not receive either an ACK handshake or a SETUP token at block  1020 , it returns to block  1016  to test for receipt of a new IN token to restart the status stage. If the IN transaction is retried, (i.e. no ACK was received) the DEF bit will not be cleared. Thus when the transaction is retried to the Default address, it will still be received by this device. 
     By clearing the DEF bit only after receipt of an ACK handshake of an IN packet or a SETUP token, the device avoids problems associated with a lost or corrupted DATA 1  packet or a lost or corrupted ACK handshake. 
     Specifically, if the DATA 1  packet is lost or corrupted, the host will not send an ACK. Consequently, the host will continue to attempt to complete the initialization process by addressing the device at the default address. Since the device has not yet cleared the default bit, the device will still respond to the default address. This allows the host to reattempt a status stage by retransmitting an IN token to the default address. 
     If the ACK from the host is lost or corrupted, the device will not yet respond to it&#39;s unique functional address. However, as the host has no indication that the ACK was not received by the device, it must assume that the transaction has properly completed and that the device will now respond to it&#39;s functional address. Consequently, the host will continue with the process of enumerating the USB network. Upon transmission of a new SETUP token to a second device on the network, the first device will clear the default address bit and set the functional address bit. The first device will now respond to the functional address only. 
     Although the embodiments described herein are with reference to specific device structure, the present invention can be applied in a variety of other devices without departing from the scope of the invention. The invention has been described with reference to an embodiment having register space for a default address bit, an functional address enable bit, and a functional address register, however alternative equivalent embodiments may implement other register and memory configurations for enabling or disabling the default and unique functional address. Those having ordinary skill in the art will certainly understand from the embodiments disclosed herein that many modifications are possible without departing from the teachings hereof. All such modifications are intended to be encompassed within the following claims.