Abstract:
The present invention concerns a method for reducing power consumption in a device, comprising the steps of (A) receiving one or more packets, (B) determining a type of each of the one or more packets and (C) suspending, waking, or partially waking the device in response to a particular type of packet.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and/or architecture for universal serial bus (USE) devices generally and, more particularly, to a method and/or architecture for reducing power consumption in USB devices. 
     BACKGROUND OF THE INVENTION 
     When implementing modern computer devices, in particular peripheral devices, it is generally desirable to provide low power consumption in the devices. Achieving a low power consumption during normal operating modes is typically a function of hardware. For example, through software control, specific hardware components of a particular device may be selected to be turned off to lower power consumption in suspend or sleep modes. However, it is often difficult to reach aggressive low power targets. 
     USB devices (which typically have current consumption of 10-100 mA) implement a low power suspend mode in which device current drops to 0-0.5 mA. The suspend mode is normally only entered on a system command (i.e., a suspend indication signal). Additionally, extensive use of the suspend mode can cause the USB device to miss USB traffic. 
     Referring to FIG. 1, an example illustrating a USB microcontroller continuously operating (i.e., on) during normal operation, since USB traffic is constantly received (i.e., traffic is received on each frame at 1 ms intervals). The microcontroller remains on, with clocks running, in order to immediately respond to any received USD traffic. Thus, conventional USB microcontrollers are either off (i.e., for a low-power state as directed by a host) or completely on during normal operation. The disadvantage of such an architecture is that full power consumption is required at all times during normal operation. In power sensitive applications, such as battery powered devices, meeting power consumption targets is a difficult challenge for USB devices. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a method for reducing power consumption in a device, comprising the steps of (A) receiving one or more packets, (B) determining a type of each of the one or more packets and (C) suspending, waking, or partially waking the device in response to a particular type of packet. 
     The objects, features and advantages of the present invention include providing a method and/or architecture for reducing power consumption in USB devices that may (i) remain in suspend mode until the beginning of a USB packet, (ii) receive synchronization fields partly asynchronously (with no clock available) and partly synchronously (with a stable clock) to verify a valid packet has been received, and/or (iii) provide a mechanism for remaining in suspend during low-speed USB keep alive markers, while waking for data packets or bus reset events. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims and drawings in which: 
     FIG. 1 is a timing diagram illustrating conventional suspend operations; 
     FIG. 2 is a block diagram illustrating an implementation of the present invention; 
     FIGS. 3 a - 3   c  are timing diagrams of approaches for reducing power in USB devices; 
     FIG. 4 is a block diagram of a preferred embodiment of the present invention; 
     FIG. 5 is a block diagram illustrating a packet of data implemented in connection with the present invention; 
     FIG. 6 is a timing diagram illustrating an operation of the present invention; 
     FIG. 7 is a timing diagram illustrating an operation of the present invention; 
     FIG. 8 is a timing diagram illustrating an operation of the present invention; and 
     FIG. 9 is a timing diagram illustrating an operation of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2, a block diagram of a system  50  is shown in accordance with a preferred embodiment of the present invention. The system  50  generally comprises a computer (e.g., a personal computer (PC))  52  and a peripheral device  54 . In one example, the peripheral device  54  may be implemented as a Universal Serial Bus (USB) peripheral device. The system  50  may provide a low power mode of operation. The computer  52  may include an interface  56 . In one example, the interface  56  may be implemented as a USB interface. The peripheral device  54  may include a microprocessor block (or circuit)  60 . In one example, the circuit  60  may be implemented as a low power consumption microprocessor circuit. The circuit  60  may interface with the host device  52  (via the interface  56 ). 
     The system  50  may provide a method for reducing power consumption in a USB Device. The system  50  may be particularly useful in battery powered applications. The system  50  may implement a low power USB device that have a low peak current consumption (e.g., 5 mA or less). 
     Referring to FIGS. 3 a - 3   c , implementations are shown that utilize suspend modes in order to lower overall average power consumption of a USB device. FIG. 3 a  shows typical USB bus traffic. FIG. 3 b  illustrates the use of suspend mode during periods of normal traffic. The device wakes up on all bus activity, including frame marker events. In some cases the device may remain awake in anticipation of data packets, so that clock circuits are operating properly at the beginning of the received data. FIG. 3 c  illustrates the use of a partial suspend mode. The USB microcontroller  100  may allow the clock generator circuit  106  and the SIE  110  to remain on, allowing the clock to be available at the beginning of data packets. The remainder of the circuitry is left in a low-power suspended state until needed. The approaches shown in FIGS. 3 a-c  reduce power consumption compared to conventional architectures. 
     Referring to FIG. 4, a diagram of a circuit  100  illustrating an implementation of the present invention is shown. The circuit  100  may be implemented as a USB microcontroller. The circuit  100  generally comprises a circuit  102 , a circuit  104 , a circuit  106 , a circuit  108  and a circuit  110 . The circuit  102  may be implemented as a traffic detect circuit. The circuit  104  may be implemented as a suspend/sleep controller circuit. The circuit  106  may be implemented as a clock generator circuit. The circuit  108  may be implemented as a processor core circuit. The circuit  110  may be implemented as a USB serial interface engine (SIE) . USB devices normally contain a serial interface engine to process incoming and outgoing USB data. 
     The circuit  104  may generate a control signal (e.g., SS) that may be used to control the sleep/suspend state of the circuits  106 ,  108  and  110 , in response to a control signal (e.g., CT) received from the traffic detect circuit  102 . The traffic detect circuit  102  may generate the signal CT in response to data (or a non-idle state) received on a signal (e.g., DATA). The traffic detect circuit  102  may also receive a signal (e.g., IRQ). The signal IRQ may indicate an interrupt (e.g., a key press on a keyboard, etc.). The clock generator  106  may generate a signal (e.g., CLK) that may be used to clock the circuit  100 . The signal CLK is generally presented to the processor  108  and the SIE  110 . 
     Alternatively, the clock generator  106  may generate a number of clock pulses for the various circuits of the system  100 . The clock pulses may have the same or different frequency and/or phase. Alternatively, an external USB SIE (not shown) may be implemented to interface with the microcontroller  100 . However, implementing an external USB SIE may have reduced integration, with associated higher costs and power consumption. 
     The clock signal CLK may remain off until a USB packet arrives. The clock signal CLK may require a fast start-up time. The clock signal CLK may be required to be ready by an end of a packet synchronization field (to be discussed in connection with FIGS.  5 - 7 ). The circuit  100  may receive the synchronization field partly asynchronously. The system  100  may remain in the suspend mode during keep alive indications for low speed USB applications. The keep alive indicators may be implemented as packets, marker signals, or other appropriate type indications in order to meet the requirements of a particular implementation. The system  100  may process the keep alive markers with minimal power, only waking on relevant data. However, the circuit  100  may also wake up for all received packets. The system  100  may be configured to optimize possible power savings. The system  100  may be implemented for all To USB type devices. Additionally, the system  100  may be implemented for UART applications or other appropriate type implementations. 
     The circuit  100  may provide an architecture for optimizing low power consumption for USB devices. Specifically, the circuit  100  may be implemented for very low power applications, such as battery-powered devices. The circuit  100  may optimize the SIE  110  to allow for proper processing of USB data while minimizing power consumption. The circuit  100  may maximize the time spent in suspend mode (e.g., with no circuitry running, such as the clock generator  106 ). 
     A battery powered device may typically have a current consumption of 1 mA. Since USB microcontrollers typically consume 10 mA or more, spending considerable time in suspend mode allows such devices to have average currents that may meet targets for low power applications. The circuit  100  may significantly reduce power, by remaining suspended for a maximum possible time. 
     The present invention may allow the circuit  100 , including the SIE  110  to remain completely off until a data packet arrives. However, the circuit  100  may wake and operate for any other device specific environmental changes, such as pressing a key on a keyboard, returning to suspend mode whenever possible. 
     Referring to FIG. 5, a set of typical USB packets is shown. USB traffic includes data packets that contain a preamble synchronization field (e.g., SYNC) followed by the packet information, such as Packet ID, addresses, data, CRC, etc. 
     Referring to FIG. 6, a detailed diagram of the SYNC field is shown. The SYNC field, includes a KJKJKJKK data pattern, where ‘J’ is the idle state (DP low, DM high, in low-speed), and ‘K’ is the active state (DM low, DP high, in low-speed). In low-speed USB mode, the keep alive frame markers may indicate that the USB bus is active such that conventional devices do not go into suspend mode. The keep alive marker may be a simple single low pulse on the DM data line, while the DP line is held low. 
     Referring to FIG. 7, a clock stabilization process of the circuit  100  is shown. The clock circuit  106  may be required to wake up and stabilize rapidly. The clock signal CLK may be required to be stabilized before the end of the packet SYNC field. Thus, the clock generation circuit  106  may be a fast starting, precision clock circuit. 
     Until the clock CLK is stable and accurate, the SIE  110  may receive the SYNC field asynchronously. During the time when the bit timing cannot be verified, the existence of a proper number of edges in the SYNC field may be verified. Once the clock signal CLK is accurate, the SIE  110  may implement the clock signal CLK to receive the remainder of the packet. As long as the clock signal CLK is available before the long bit (e.g., kk) at the end of the synchronization is received, the packet may be received properly. However, the precise point in the packet when the clock must be valid may vary with the particular SIE design, although a proper clock will generally be required sometime during the synchronization field. 
     The circuit  100  may maximize the time spent in suspend mode. The circuit  100  may not wake up until a USB packet begins to arrive (e.g., by recognizing the USB ‘K’ state at the beginning of the packet.) The circuit  100  may return to suspend mode immediately after the end of the packet, the ‘kk’ state or if no further action is required from the device (e.g., if the packet is not addressed to the device). 
     For low-speed USB application, a keep alive marker is sent at least once during every 1 ms frame. Processing the keep alive packets in the low-speed USB mode increases unnecessary power consumption. For a constantly-suspending device, the keep alive markers carry no additional information (e.g., the keep alive stops the device from suspending). Therefore, it may be desirable to optionally ignore the keep alive to spend as little power as possible on processing such events. The keep alive may be distinguished from the beginning of a normal USB data packet. Thus, the keep alive may be ignored to avoid initiating the power-up sequence. 
     Referring to FIG. 8, an example keep alive signal is shown. The keep alive signal generally comprises two data lines (e.g., DM and DP) . The signals DM and DP may be low for approximately 2 low-speed bit times (nominally 1.33 microseconds). A bus-reset signal also forces the signals DM and DP low, but for a longer time (at least 10 ms). When both the signals DM and DP are low, a single-ended zero (SE 0 ) state occurs. To minimize power, a device may ignore keep alive signals (remaining in a suspend state). However, the device may awake on a bus reset to take appropriate reset actions. 
     To distinguish the keep alive from data packets or a bus reset, the device may be configured to awake if either (i) the USB ‘K’ state occurs (e.g., start of a data packet) or (ii) a SE 0  occurs. The SEQ may be distinguished from a keep alive with an internal timer such as a one-shot type circuit, configured to it provide a time reference longer than a keep alive, but shorter than a bus reset. The timer could be made with low-power techniques and without a need for an accurate clock, since the timing requirements are not critical. Such a timer may be implemented on a typical integrated circuit as part of the fabrication of the circuit  100 . 
     Referring to FIG. 9, an overall power usage for the device  100  is shown. The device  100  is typically placed in suspend mode when no activity is present. A small amount of power may be consumed to process keep alive packets (via the traffic detect circuit  102 ). However, during other USB packets, the clock generator  106  and the SIE  110  may wake and process the packet accordingly. The device  100  may remain awake to process the packet, then return to suspend mode. The particular circuits of the chip required to remain awake may vary with application. Additionally, the device  100  may wake for non-USB activity, such as pressing a key of a keyboard. The circuit  100  may optionally wake the remainder of the chip only if a received packet requires action from the device (e.g., only when the packet is addressed to the specific device). 
     The circuit  100  generally remains in a suspend mode until the beginning of a USB packet. The circuit  100  may also receive the synchronization field both partly asynchronously (no clock available) and partly synchronously (with a stable clock) to verify a valid packet has been received. The circuit  100  may immediately return to suspend mode after packets that require no further action have been processed. The circuit  100  may remain in suspend during a low-speed USB keep alive state, while waking for data packets or bus reset events. 
     The circuit  100  may allow a given USB device to achieve essentially the minimum possible power consumption by maximizing the time spent in suspend mode. The circuit  100  may be implemented for battery powered applications. The circuit  100  may lower power consumption in USB devices by remaining suspended until data packets are received. For example, the circuit  100  may reduce power in a low-speed USB device by remaining suspended during keep alive packets. The circuit  100  may remain in suspend mode until the beginning of a USB packet. The circuit  100  may provide a mechanism for remaining in suspend during a low-speed USB keep alive, while waking for data packets or bus reset events. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.