Patent Publication Number: US-8989071-B2

Title: Inter-chip data communications with power-state transition management

Description:
PRIORITY INFORMATION 
     This application claims the benefit of U.S. Provisional Application No. 61/695,601, entitled “Inter-Chip Data Communications With Power-State Transition Management,” filed Aug. 31, 2012. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure relates generally to wireless communication systems and devices, and more particularly to methods, apparatus, and integrated circuits for inter-chip data communications with power-state transition management. 
     2. Description of the Related Art 
     In recent years, wireless devices such as smart phones and tablet computers have become increasingly sophisticated. In addition to supporting telephone calls, many mobile devices now provide access to the internet, email, text messaging, and navigation using the global positioning system (GPS). Furthermore, many mobile devices are capable of operating sophisticated applications, many of which may utilize the functionality mentioned above. Wireless devices that support such sophisticated functionality often include many components, each of which consume power. Power in such wireless devices is often provided by a battery. As such, there is often a tradeoff between controlling power consumption of the many components of a wireless device and increasing performance of those same components. 
     SUMMARY 
     Various example methods for inter-chip data communications are disclosed. One example method of inter-chip data communications between a power-managed integrated circuit (IC) and a peer IC includes generating, by the peer IC, a data frame to be transmitted to the power-managed IC. The peer IC, in generating the data frame, may also prepend a discardable preamble of a predefined size to a payload of the data frame. The predefined size of discardable preamble may be a size not less than a size of data discarded by the power-managed IC upon the power-managed IC receiving a data frame while in a low-power state. The peer IC may then transmit the data frame, with the discardable preamble, to the power-managed IC. 
     In some embodiments, the power-managed IC may receive a data frame with a discardable preamble from a peer IC while the power-managed IC is in a low-power state. In response to receiving the data frame, the power-managed IC may begin to exit the low-power state and discard a portion of the data frame while exiting the low-power state. The portion of the data frame discarded by the power-managed IC may be no greater in size than the size of the discardable preamble. That is, the power-managed IC may discard a portion of the data frame without discarding any payload data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  sets forth a block diagram of one embodiment of a wireless communication system. 
         FIG. 2  sets forth a block diagram of one embodiment of a wireless communication device shown in  FIG. 1 . 
         FIG. 3  sets forth a flow chart illustrating an exemplary method of inter-chip data communications. 
         FIG. 4  sets forth a flow chart illustrating another exemplary method of inter-chip data communications in which a peer IC calculates a size of a discardable frame preamble. 
         FIG. 5  sets forth a flow chart illustrating another exemplary method of inter-chip data communications in which a peer IC dynamically determines whether to prepend a discardable preamble to the payload of a data frame. 
         FIG. 6  sets forth a flow chart illustrating another exemplary method of inter-chip data communications in which a power-managed IC exits from a low-power state to receive a set of data from a peer IC and re-enters the low-power state aggressively. 
         FIG. 7A  sets forth a line drawing illustrating an example set of data frames generated by a peer IC for inter-chip data communications. 
         FIG. 7B  sets forth a line drawing illustrating an example set of data frames received by a power-managed IC while in a low-power state. 
     
    
    
     Specific embodiments are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description are not intended to limit the claims to the particular embodiments disclosed, even where only a single embodiment is described with respect to a particular feature. On the contrary, the intention is to cover all modifications, equivalents and alternatives that would be apparent to a person skilled in the art having the benefit of this disclosure. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. 
     As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to. 
     Various units, circuits, or other components may be described as “configured to” perform a task or tasks. In such contexts, “configured to” is a broad recitation of structure generally meaning “having circuitry that” performs the task or tasks during operation. As such, the unit/circuit/component can be configured to perform the task even when the unit/circuit/component is not currently on. In general, the circuitry that forms the structure corresponding to “configured to” may include hardware circuits. Similarly, various units/circuits/components may be described as performing a task or tasks, for convenience in the description. Such descriptions should be interpreted as including the phrase “configured to.” Reciting a unit/circuit/component that is configured to perform one or more tasks is expressly intended not to invoke 35 U.S.C. §112, paragraph six, interpretation for that unit/circuit/component. 
     The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims. 
     DETAILED DESCRIPTION 
       FIG. 1  sets forth a block diagram of one embodiment of a wireless communication system. The system of  FIG. 1  is one example of any of a variety of wireless communication systems. The wireless communication system  10  includes a base station  102  which communicates over a wireless transmission medium such as, for example, an over the air interface with one or more user equipment (UE) devices,  106 A through  106 N. The base station  102  is also coupled a network  100  via another interface, which may be wired or wireless. Components identified by reference designators that include both a number and a letter may be referred to by the number only where appropriate. 
     The base station  102  may be a base transceiver station (BTS) or cell site, and may include hardware that enables wireless communication with one or more of the UEs  106 . The base station  102  may also be equipped to communicate with the network  100 . Thus, the base station  102  may facilitate communication between the UEs  106  and/or between the UEs  106  and the network  100 . The communication area (or coverage area) of the base station  102  may be referred to as a “cell.” In various embodiments, the base station  102  and the UEs may be configured to communicate over the transmission medium using any of various wireless communication radio access technologies such as LTE, eHRPD, GSM, CDMA, WLL, WAN, WiFi, WiMAX, etc. In embodiments that communicate using the eHRPD standard, the BTS  102  may be referred to as an HRPD BTS, and the network  100  may include an eAN/ePCF and a number of gateways including HRPD gateway (HSGW), a PDN gateway (P-GW), and a number of policy and packet control functions that may be associated with a service provider, for example. 
     In one embodiment, each of the UEs  106 A- 106 N may be representative of a device with wireless network connectivity such as a mobile phone, a hand-held device, a computer or a tablet, or virtually any type of wireless device. As described further below, the UE  106  may include at least one processor that is configured to execute program instructions stored in a memory. Accordingly, in some embodiments, the UE  106  may perform one or more portions of the functionality described below by executing such stored instructions. However, in other embodiments, the UE  106  may include one or more hardware elements and/or one or more programmable hardware elements such as an FPGA (field-programmable gate array) that may be configured to perform the one or more portions the functionality described below. In still other embodiments, any combination of hardware and software may be implemented to perform the functionality described below. 
     In the system  10  of  FIG. 1 , any of the UEs  106  may include a power-managed integrated circuit (IC) and peer IC. Either of the ICs may be implemented as any one of a variety of components including, for example, a processor, memory management unit, an I/O interface, a wireless communication receiver, a wireless communication transmitter, and others. 
     The power-managed IC is referred to as ‘power-managed’ in that the IC is configured to vary between a low power-state and one or more other power-states. Such an IC, for example, may enter a low-power state after a predefined time of inactivity. In the low-power state, one or more components of the power-managed IC may be powered down or off, the IC&#39;s core operating voltage may be reduced, the IC&#39;s clock speed may be throttled, and other functionality may be otherwise reduced. In this way, the power-managed IC consumes less power in a low-power state than when operating in a higher-power state. 
     The peer IC is referred to as a ‘peer’ in that the peer IC is coupled for data communications to the power-managed IC. The peer IC may communicate with the power-managed IC by transmitting one or more data frames serially to the power-managed IC over a bus or other data communications link. 
     The peer IC of a UE  106  in the example system of  FIG. 1  may be configured to generate a data frame for transmission to the power-managed IC of the UE  106 . In response to receiving a data frame from the peer IC when the power-managed IC is in a low-power state, the reception of a data frame initiates an exit from the low-power state. At the time the power-managed IC begins an exit from the low-power state, and for some time thereafter, components of the power-managed IC configured to process the received data may not be in a fully operational state. For this reason, the power-managed IC may, while exiting the low-power state, drop or discard a portion of the received data frame while exiting the low-power state. 
     To reduce the probability of the power-managed IC dropping useful payload data from a data frame while exiting a low-power state, the peer IC of a UE  106  may also be configured to prepend a discardable preamble of a predefined size to a payload while generating the data frame. The term ‘prepend’ as used here refers to generating a preamble to be transmitted prior to, or before, a payload. The predefined size of the preamble may be a size not less than a size of data discarded by the power-managed IC upon the power-managed IC receiving a data frame while in a low-power state. The discardable preamble may include a predefined value recognizable by the power-managed IC, such as a value of ‘0’ for each bit of every byte of the preamble, a value of ‘1’ for each bit of every byte of the preamble, or some other predefined pattern of bits. 
     The term ‘payload’ as used here refers to encoded information intended to be received and processed by a receiver (in this example a power-managed IC). Such a payload is contrasted with a discardable preamble as the term is used here. A discardable preamble contains no encoded information intended by a transmitter of the preamble to be processed or consumed by the receiver. In fact, the transmitter of the data frame intends for the entire discardable preamble to be completely discarded. 
     After generating the data frame with the discardable preamble prepended to the data frame&#39;s payload, the peer IC transmits the data frame. The peer IC may transmit the data frame serially, such that the discardable preamble is the first data transmitted to the power-managed IC followed by payload data. 
     The power-managed IC of the UE  106  may then receive the data frame from the peer IC. If the power-managed IC is in a low-power state, the reception of the data frame causes the power-managed IC to begin to exit the low-power state. During the exit, the power-managed IC may discard a portion of the data frame where the discarded portion is of a size not greater than the size of the discardable preamble. That is, the portion of the data frame discarded is some portion, up to the entirety, of the discardable payload. In this way, the power-managed IC may discard, while exiting, a portion of the data frame that includes only discardable preamble data without discarding payload data. As such, there is no need for the peer IC to re-transmit discarded payload data. 
     In some embodiments, the peer IC may transmit a data frame with a discardable preamble to the power-managed IC even when the power-managed IC is not a low-power state. If the power-managed IC is not in a low-power state when the power-managed IC receives the data frame from the peer IC, the power-managed IC may discard the preamble and process the payload. 
     It is noted that the peer IC and power-managed IC may, at times, swap roles. That is, the peer IC in may also be configured to vary between power-states and the power-managed IC may be configured to prepend discardable preamble to data frames intended for the peer IC. Any IC may be configured as a peer IC, as a power-managed IC, or as both. 
     For further explanation,  FIG. 2  sets forth a block diagram of one embodiment of a wireless communication device shown in  FIG. 1 . The UE  106  includes one or more processors  202  (or one or more processor cores  202 ) which are coupled to display circuitry  204  which is in turn coupled to the display  240 . The display circuitry  204  may be configured to perform graphics processing and provide display signals to the display  240 . 
     The one or more processors  202  are also coupled to a memory management unit (MMU)  220  and to a receiver/transmitter (R/T) unit  230 . The MMU  220  is coupled to a memory  206 . The UE  106  also includes an I/O interface  210  that is coupled to the processor(s)  202 , and may be used for coupling the UE  106  to a computer system, or other external device. It is noted that in one embodiment the components shown within UE  106  of  FIG. 2  may be manufactured as stand alone components. In other embodiments, however, various ones of the components may be part of one or more chipsets or part of a system on chip (SOC) implementation. 
     In various embodiments, the processors  202  may be representative of a number of different types of processors that may be found in a wireless communication device. For example, the processors  202  may include general processing capability, digital signal processing capability, as well as hardware accelerator functionality, as desired. The processors  202  may include baseband processing and therefore may digitally process the signals received by the R/T unit  230 . The processors  202  may also process data that may be transmitted by the R/T unit  230 . The processors  202  may also perform a number of other data processing functions such as running an operating system and user applications for the UE  106 . 
     In one embodiment, the MMU  220  may be configured to receive addresses from the one or more processors  202  and to translate those addresses to locations in memory (e.g., memory  206 ) and/or to other circuits or devices, such as the display circuitry  204 , R/T unit  230 , and/or display  240 . The MMU  220  may also return data to one or more of the processors  202  from the locations in memory  206 . The MMU  220  may be configured to perform memory protection and page table translation or set up. In some embodiments, the MMU  220  may be included as a portion of one or more of the processors  202 . 
     The R/T unit  230  may, in one embodiment, include analog radio frequency (RF) circuitry for receiving and transmitting RF signals via the antenna  235  to perform the wireless communication. The R/T unit  230  may also include down-conversion circuitry to lower the incoming RF signals to the baseband or intermediate frequency (IF) as desired. For example, the R/T unit  230  may include various RF and IF filters, local oscillators, mixers, and the like. Since the UE  106  may operate according to a number of radio access technologies, the R/T unit  230  may include a corresponding number of RF front end portions to receive and down-convert, as well as up-convert and transmit the respective RF signals of each technology. 
     In some embodiments, inter-chip data communications between a peer IC  214  and a power-managed IC  212  as mentioned above may be implemented with processors. The processors  202  in the UE  106  of  FIG. 2 , for example, include a power-managed IC  212  implemented as a power-managed processor  202   a  and a peer IC  214  implemented as a peer processor  202   b , each of which may be configured for inter-chip data communications as described above. In various embodiments, the processors  202  may execute software stored within a memory, such as memory  206  for example, to perform functionality associated with inter-chip data communications as mentioned above. In other embodiments, the processors  202  may include hardware configured to perform inter-chip data communications as described above. In the UE  106  of  FIG. 2 , for example, the each of the power-managed processor  202   a  and the peer processor  202   b  includes a Universal Asynchronous Receiver/Transmitter (UART) ( 208   a ,  208   b ) that is configured to perform functionality associated with inter-chip data communications mentioned above. 
     UART is a hardware component configured to translate data between parallel and serial forms. UARTs are commonly used in conjunction with communication standards such as EIA, RS-232, RS-422, or RS-485. The ‘universal’ designation indicates that the data format and transmission speeds are configurable and that the actual electric signaling levels and methods, such as differential signaling and the like, are typically handled by a special driver circuit (not shown in  FIG. 2 ) external to the UART. It is noted that UARTs are but one example serial communications component among a variety of possible components that may be configured to perform inter-chip data communications as mentioned above. Other examples include a serial peripheral interface (SPI), inter-integrated circuit (I2C), and the like. 
     For further explanation,  FIG. 3  sets forth a flow chart illustrating an exemplary method of inter-chip data communications. Portions of the method of  FIG. 3  may be carried out by one or more components of the example UE  106  of  FIG. 2 , such as the power-managed IC  212  and the peer IC  214 . For this reason and for purposes of clarity, the description of the method of  FIG. 3  refers to components of  FIG. 2 . 
     In the method of  FIG. 3 , the power-managed IC  212  may enter into a low-power state (block  302 ). The power-managed IC  212  may enter into a low-power state (block  302 ) for a variety of reasons, including for example, due to inactivity for a predefined period of time. The power-managed IC may maintain an internal timer that begins at a predefined amount of time and continually counts down. Upon activity, the timer may be restarted, and countdown may begin again. When the timer reaches zero, the power-managed IC  212  may enter the low-power state. 
     The peer IC  214  in the example of  FIG. 3  may generate a data frame (block  304 ). The peer IC  214  may generate a data frame for various reasons. For example, a software application or hardware component may cause the peer IC  214  to generate the data frame from purposes of data transmission to the power-managed IC  212 . The peer IC may, in generating the data frame, prepend a discardable preamble of a predefined size to a payload of the data frame (block  306 ). The predefined size may be a size not less than a size of data discarded by the power-managed IC  212  upon the power-managed IC receiving a data frame while in a low-power state. For example, if a power-managed IC typically discards 32 bytes of data upon reception of a data frame while in a low-power state, the discardable preamble may be no less than 32 bytes in size. 
     Once the peer IC  214  generates the data frame, the peer IC  214  may transmit the data frame to the power-managed IC  212  (block  308 ). The peer IC  214  may transmit the data frame serially to the power-managed IC  212 , beginning with the discardable preamble, followed by the payload of the data frame. 
     The power-managed IC  212 , while in a low-power state may receive the data frame from the peer (block  310 ). In response to receiving the data frame, the power-managed IC  212  may then begin exiting the low-power state (block  312 ). During the exit, the power-managed IC may increase power supply, increase clock frequency, disable power gates, disable clock gates, and the like to one or more components so that the components are fully operational. At the time the data frame is received and the power-managed IC begins the exit from the low-power state, however, the components of the power-managed IC  212  responsible for processing data received from the peer IC  214  are not fully operation. As such, the power-managed IC may discard a portion of the data frame while exiting the low-power state (block  314 ). The portion of the data frame that the power-managed IC discards may be of a size not greater than the size of the discardable preamble of the data frame. Consider, for example, that the discardable preamble is 32 bytes in size (length). In such an example embodiment, the power-managed processor may discard any portion of the first 32 bytes of the data frame. In this way, the power-managed IC may discard a portion of the data frame without discarding any of the payload of the data frame. 
     For further explanation,  FIG. 4  sets forth a flow chart illustrating another exemplary method of inter-chip data communications. The method of  FIG. 4  is similar to the method of  FIG. 3  in that portions of the method of  FIG. 4  may also be carried out one or more components of the example UE  106  of  FIG. 2 , such as the power-managed IC  212  and the peer IC  214 . For this reason and for purposes of clarity, the description of the method of  FIG. 4  refers to components of  FIG. 2 . The method of  FIG. 4  is also similar to the method of  FIG. 3  in that the method of  FIG. 4  includes many of the same blocks, where the corresponding blocks are numbered the same and operate in manner described above, with variations described below. 
     In the method of  FIG. 4 , prior to the power-managed IC  212  entering a low-power state (block  302 ), the power managed IC  212  may inform the peer IC  214  of a maximum expected time for exiting the low-power state. The maximum expected time for exiting the low-power state is a maximum expected duration between a time the power-managed IC begins to exit the low-power state and a time at which the components of the power-managed IC  212  to become fully operational. The maximum expected time for exiting the low-power state is said to be ‘expected’ because the actual time required to become fully operational from a low-power state may vary slightly with varying operating and environmental conditions. 
     The peer IC  214  when generating a data frame (block  304 ) in the method of  FIG. 4  may calculate a predefined size of a discardable preamble of the data frame in dependence upon the maximum expected time for the power-managed IC to exit the low-power state (block  404 ). That is, the size of the discardable preamble may vary in the method of  FIG. 4  with the time expected for the power-managed IC to exit the low-power state. The longer the power-managed IC  212  takes to fully exit the low-power state, the longer the components of the power-managed IC  212  responsible for processing received frame data take to become fully operation. Thus, the longer the power-managed IC  212  takes to fully exit the low-power state, the greater the size of data discarded by the power-managed processor during the exit process. The peer IC  214  in the method of  FIG. 4 , given the maximum expected time for the power-managed IC  212  to exit the low-power state, may calculate a size of the discardable preamble so as to insure that the preamble is large enough in size to insure that the power-managed processor discards only portions of the preamble rather than payload data. Further, peer IC  214  may calculate the size of the discardable preamble so as to insure that the preamble is not needlessly large in size. 
     For further explanation,  FIG. 5  sets forth a flow chart illustrating another exemplary method of inter-chip data communications. The method of  FIG. 5  is also similar to the method of  FIG. 3  in that the method of  FIG. 5  may be carried out one or more components of the example UE  106  of  FIG. 2 , such as the power-managed IC  212  and the peer IC  214 , and the method of  FIG. 5  includes many of the same blocks as  FIG. 3 , where the corresponding blocks are numbered the same and operate in manner described above, with variations described below. 
     The power-managed IC  212 , prior to entering a low-power state (block  302 ) in the method of  FIG. 5 , may inform the peer IC  214  of a minimum expected time between the power-managed IC exiting and re-entering the low-power state (block  502 ). The minimum expected time between the power-managed IC exiting and re-entering the low-power state is the minimum duration of time the power-managed IC will not be in the low-power state. In some embodiments, as mentioned above, the power-managed IC may be configured to enter a low-power state after a predefined period of inactivity. In some embodiments, then, the minimum amount of time that a power-managed IC may be fully operation before re-entering a low-power state may be the predefined period of inactivity. 
     Once informed of the minimum expected time in the method of  FIG. 5 , the peer IC  214 , may, in generating a data frame for transmission to the power-managed IC  212  (block  304 ), determine whether the power-managed IC is currently in a low-power state in dependence upon a time of the power-managed IC&#39;s most recent exit from the low-power state and the minimum expected time between exiting and re-entering the low-power state (block  504 ). To determine whether the power-managed IC  212  is currently in a low-power state, the peer IC  214  may calculate a duration of time since the power-managed IC  212  most recently exited from the low-power state. The peer IC  214  may then compare the calculated duration to the minimum expected time before re-entering the low-power state. If the calculated duration is greater than or equal to the minimum expected time before re-entering the low-power state, the peer IC  214  may determine that the power-managed IC  212  is currently in a low-power state. If the calculated duration is less than the minimum expected time before re-entering the low-power state, the peer IC  214  may determine that the power-managed IC  212  is not currently in a low-power state. 
     It is noted that the outcome of the determination as to whether the power-managed IC is currently in a low-power state (block  504 ) may not be accurate in all cases. That is, the peer IC may not be absolutely certain at all times as to whether the power-managed IC is currently in the low-power state. Instead, given the minimum expected time between exiting and re-entering the low-power state (which, by its very nature as a maximum, is an approximation of sorts), the peer IC makes an educated guess as to whether the power-managed IC is currently in a low-power state. In embodiments in which the power-managed IC is not currently in the low-power state but receives a data frame with a discardable preamble, the power-managed IC may discard the preamble and process the payload as mentioned above. 
     The peer IC  214  may then prepend a discardable preamble to the payload of the data frame (block  306 ) only if the peer IC determines that the power-managed IC  212  is currently in the low-power state. If the peer IC  214  determines that the power managed IC  212  is not currently in the low power state, the peer IC  214  may prepend a preamble that is not discardable—a preamble having a size less than the size of the discardable preamble—to the payload of the data frame (block  506 ). In another embodiment, the peer IC  214  may not prepend any preamble if the peer IC  214  determines that the power managed IC  212  is not currently in the low power state. In this way, the peer IC  214  is configured to reduce superfluous data traffic when the peer IC has determined that the power-managed IC is not in a low-power state and thus will not discard a portion of the data frame while exiting the low-power state. 
     For further explanation,  FIG. 6  sets forth a flow chart illustrating another exemplary method of inter-chip data communications. The method of  FIG. 6  is also similar to the method of  FIG. 3  in that the method of  FIG. 6  may be carried out by one or more components of the example UE  106  of  FIG. 2 , such as the power-managed IC  212  and the peer IC  214 , and the method of  FIG. 6  includes many of the same blocks as  FIG. 3 , where the corresponding blocks are numbered the same and operate in manner described above, with variations described below. 
     The peer IC  214  may generate a set of data frames to be transmitted to the power-managed IC  212  (block  602 ) and may prepend a discardable preamble to a first data frame of the set (block  604 ). As mentioned above, the power-managed IC  212  may be configured to enter the low-power state after a predefined period of inactivity. The peer IC  214 , however, may be configured to send the data frames of the set one after another, with little time in between the frames. While the first data frame may cause the power-managed IC  212  to exit the low-power state, the following data frames prohibit the power-managed IC from re-entering the low-power state. As such, the power-managed IC  212  may discard data only from the first data frame during the exit from the low-power state. 
     The peer IC  214  in the method of  FIG. 6  may also append a transmission complete notification to a payload of a last data frame of the set of data frames to be transmitted to the power-managed IC  212  (block  606 ). The term ‘append’ as used here refers to generating a transmission complete notification to be transmitted after a payload. The transmission complete notification may be a predefined value or a flag, recognize and well known by the power-managed IC, that indicates the completion of a transmission of a set of frames and some time with no further transmission from the peer IC  214 . 
     The peer IC  214  in the method of  FIG. 6  may transmit the set of data frames to the power-managed IC beginning with the first data frame that includes the discardable preamble and ending with the last data frame that includes the transmission complete notification (block  610 ) and the power-managed IC  212  may receive the set of data frames (block  612 ). 
     In response to receiving the first data frame of the set, the power-managed IC  212  begins exiting the low-power state (block  312 ) and discards a portion of the first data frame without discarding any of the payload of the first data frame (block  314 ). The power-managed IC  212 , in response to receiving the last data frame of the set, may immediately re-enter the low-power state (block  614 ). That is, once the power-managed IC receives and processes the transmission complete notification of the last data frame, the power-managed IC need not wait for a predefined period of inactivity, but rather may immediately (or nearly so) re-enter the low-power state. With such inbound framing techniques, power-state transitions of the power-managed IC may be aggressively and actively controlled. Such aggressive control of power-state transitions of the power-managed IC may provide a reduction in power consumption. Further, the inbound framing techniques may also provide increased data communications efficiency be insuring that payload data is not dropped during a power-managed IC&#39;s exit from a low-power state. 
     For further explanation,  FIG. 7A  sets forth a line drawing illustrating an example set of data frames generated by a peer IC for inter-chip data communications as described above with reference to  FIG. 3 ,  FIG. 4 ,  FIG. 5 , and  FIG. 6 .  FIG. 7B  sets forth a line drawing illustrating the same example set of data frames as received by a power-managed IC while in a low-power state. 
     The example set  700   a  of data frames generated by a peer IC includes a first data frame  702 , a second data frame  708 , and a last data frame  712 . Although only three data frames are depicted in the example of  FIG. 7A , any number of data frames may be included in such a set. 
     In the example of  FIG. 7A , a peer IC has prepended to a payload  706  of the first data frame  702  a discardable preamble  704 . As mentioned above, the size of the discardable preamble is greater than the size of data generally discarded by a power-managed IC upon receiving a data frame when in a low-power state. 
     In generating the second data frame  708  in the set  700   a , the peer IC has generated only a payload  710 . The peer IC may transmit the second data frame  708  relatively soon after transmitting the first data frame  702  to the power-managed IC. The first data frame will cause the power-managed IC to exit the low-power state and, as such, the second data frame  708  needs no discardable preamble. 
     For the last data frame  712  in the set  700   a , the peer IC has appended to the payload  714  of the last data frame  712  and transmission complete notification implemented as an end-of-transmission flag. The end-of-transmission flag indicates to the power-managed IC that the peer IC will not be transmitting additional data frames for at least some appreciable amount of time. 
     In  FIG. 7B , the power-managed IC receives the set  700   b  of data frames beginning with the first data frame  702 . Responsive to receiving the first data frame  702 , the power-managed IC begins exiting the low-power state and, while exiting, discards a portion  718  of the first data frame  702 . In the example of  FIG. 7B , the power-managed IC discards the entire preamble  704  as depicted by the discarded preamble  718 . In this example, the power-managed IC, in discarding the preamble  704 , does not discard the payload  706  of the first data frame  702 . 
     In  FIG. 7B , the power-managed IC may also receive the second data frame  710  and the second data frame&#39;s payload  710 . Finally, the power-managed IC may receive the last data frame  712 , process the payload  714  of the last data frame  712 , and process the end-of-transmission flag  716 . Immediately (or relatively so) upon and responsive to processing the end-of-transmission flag  716 , the power-managed IC may re-enter the low power state. That is, the power-managed IC need not wait for a period of inactivity to expire prior to re-entering the low-power state. 
     For the last data frame  712  in the set  700   a , the peer IC has appended to the payload  714  of the last data frame  712  and transmission complete notification implemented as an end-of-transmission flag. The end-of-transmission flag indicates to the power-managed IC that the peer IC will, for at least some appreciable amount of time, transmit no additional data frames. 
     Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.