WO2007107938A1

WO2007107938A1 - A device and a method for saving energy by sharing a buffer

Info

Publication number: WO2007107938A1
Application number: PCT/IB2007/050922
Authority: WO
Inventors: Ozcan Mesut
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-03-22
Filing date: 2007-03-16
Publication date: 2007-09-27

Abstract

A device and a method for saving energy by sharing a buffer are disclosed. The device (100) comprises at least a first processing unit (610) for processing a first stream (210) and a second processing unit (620) for processing a second stream (250) wherein the first processing unit (610) and the second processing unit (620) process the first stream (210) and the second stream (250) independently from each other. A buffer (110) for common use by the first processing unit (610) and the second processing unit (620) is optimally distributed into a first portion (111) and a remaining portion (112) for the first processing unit (610) and the second processing unit (620) respectively. The buffer (110) is distributed by a means for allocation (630) based upon first power consumption characteristics (640) of the first processing unit (610) and second power consumption characteristics (650) of the second processing unit (620).

Description

A device and a method for saving energy by sharing a buffer

FIELD OF THE INVENTION

The invention relates to a device for saving energy by sharing a buffer. The invention further relates to a method for saving energy by sharing a buffer. The invention further relates to a program element.

The invention further relates to a computer-readable medium.

BACKGROUND OF THE INVENTION

All electronics devices consume power. The power consumed translates directly into cost for an end user. For example, the power consumed by a home video cassette recorder results in an energy bill. For mobile devices the power consumed also translates into a certain time for which a device will operate. For example, when a portable audio player runs on batteries. In general saving power is always of benefit to an end user. This is true for both situations in the home and on the move. Electronic devices operating in the Consumer Electronics domain generally have further requirements of providing a guaranteed quality of service to an end user. For example, an audio playback device should always play the audio desired by an end user and a video playback device should always play the video desired by an end user and this should be performed without noticeable glitches in the audio or video playback. For dedicated devices it has been possible to tailor Consumer Electronics devices to provide a guaranteed quality of service in combination with optimized power consumption by using a buffer. The buffer is generally the remaining memory space that is not used by any processes running on the device. In this way all available remaining space is used to optimize the power consumption. For example, WO 2004/061843 provides energy efficient disk scheduling for mobile applications in which the standby time of a disk supplying information is adaptively extended to optimize power consumption. Use is made of a buffer to hold data for processing whilst the disk may be set in standby mode or powered-off completely. An energy saving scheduling means ensures that the quality of service remains guaranteed by filling the buffer when necessary. Multiple simultaneous audio and video streams may also be supported by summing the individual data rates of the individual streams to provide a total bit rate. The buffer is then optimally distributed according to the ratio of the processing rate, or data rate, of the individual streams. However, it is assumed that the disk must process all streams, i.e. they must all read from or written to the disk. In general, in the prior art, it is assumed that streams are processed in a sequential manner and that there is a single dominant power consumption process step upon which the buffer may be optimized. In WO 2004/061843 the single dominant power consumption process step is the disk access.

More recently, newer devices have emerged in which it has become possible to process multiple audio and video streams not only simultaneously but also fully independently from each other. For example, a mobile audio/video device with storage and networking facilities may stream information from the built-in storage device to a remote display simultaneously and independently from receiving, decoding and displaying video on a local display from a remote storage device. Such newer devices would also benefit from the optimization of power consumption in combination with providing a guaranteed quality of service, however, the prior art gives no indications as to how this may optimally be achieved. The inventors recognizing this problem devised the present invention.

BRIEF SUMMARY OF THE INVENTION

The present invention seeks to address one or more shortcomings of the prior art.

Accordingly, there is provided, in a first aspect of the present invention, a device for saving energy by sharing a buffer, the device comprising the buffer, the buffer comprising at least a first portion and a remaining portion, a first processing unit for processing a first stream, the first processing unit having first power consumption characteristics, a second processing unit for processing a second stream, the second processing unit having second power consumption characteristics and a means for allocating the first portion to the first processing unit and the remaining portion to the second processing unit characterized in that the device is adapted to process the first stream and the second stream independently and the means for allocating are adapted to allocate the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.

The use of a buffer provides a reduction in power consumption by allowing component units, within a device, that are processing the independent streams to operate in an efficient burst mode and then be shutdown to conserve power and therefore energy. The buffer then supplies information at the stream rate to provide a guaranteed quality of service whilst the component units are powered down. Also, the average power consumed reduces with increasing size of the buffer. Therefore by allocating the buffer distribution between the component units initially according to the power consumption characteristics of the component units it is possible to optimally share the buffer space available by providing the majority of the buffer space to the component unit consuming the majority of the power. For each component unit it is then possible to further allocate the distributed buffer for individual streams according to the prior art.

According to a second aspect of the invention a method for saving energy by sharing a buffer is provided, the method comprising the steps of determining first power consumption characteristics of a first processing unit, determining second power consumption characteristics of a second processing unit and allocating a first portion of the buffer to the first processing unit and the remaining portion of the buffer to the second processing unit characterized in that the first processing unit and the second processing unit process streams independently and the step of allocating further allocates the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.

According to a third aspect of the invention a program element is provided, the program element directly loadable into the memory of a programmable device, comprising software code portions for performing, when said program element is run on the device, the method steps of determining first power consumption characteristics of a first processing unit, determining second power consumption characteristics of a second processing unit and allocating a first portion of a buffer to the first processing unit and the remaining portion of the buffer to the second processing unit characterized in that the first processing unit and the second processing unit process streams independently and the step of allocating further allocates the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.

According to a fourth aspect of the invention a computer-readable medium is provided, the computer-readable medium directly loadable into the memory of a programmable device, comprising software code portions for performing, when said code portions are run on the device, the method steps of determining first power consumption characteristics of a first processing unit, determining second power consumption characteristics of a second processing unit and allocating a first portion of a buffer to the first processing unit and the remaining portion of the buffer to the second processing unit characterized in that the first processing unit and the second processing unit process streams independently and the step of allocating further allocates the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.

In one embodiment a processing unit may be a means for non-volatile storage. Such means for non- volatile storage are commonly applied in Consumer Electronics devices and they generally consume a significant amount of power during operation. Therefore, reducing the power consumption of such a means for non- volatile storage is beneficial.

In a further embodiment a processing unit may be a means for communication. Such means for communication are also commonly applied in Consumer Electronics devices and again, they generally consume a significant amount of power during operation. In another embodiment the first portion and the remaining portion may be allocated based further upon the processing rate of a first stream and the processing rate of a second stream. Taking into account also the processing rates of the streams allows further optimization of the buffer distribution between the processing devices.

In yet another embodiment a stream characteristics input may be provided. The stream characteristics input may receive stream characteristics from, for example, an application. Such an application may be under control of a user. Taking into account also the characteristics of the streams allows further optimization of the buffer distribution between the processing devices.

In an embodiment the first power consumption characteristics may comprise at least one of the group consisting of a data rate, a non-operating power consumption in a non- operating mode, an operating power consumption in an operating mode, a cycle time period required to transition from the operating mode to the non-operating mode and a cycle energy usage required to transition from the operating mode to the non-operating mode. Such power consumption characteristics provide a simple yet powerful model of the power consumption of the first processing unit.

In another embodiment the second power consumption characteristics may comprise at least one of the group consisting of a data rate, a non-operating power consumption in a non-operating mode, an operating power consumption in an operating mode, a cycle time period required to transition from the operating mode to the non-operating mode and a cycle energy usage required to transition from the operating mode to the non- operating mode. Such power consumption characteristics provide a simple yet powerful model of the power consumption of the second processing unit.

In a further embodiment the stream characteristics input may comprise a first data rate required of the first processing unit, a second data rate required of the second processing unit and a maximum size of the buffer. Such information can further improve the distribution of the buffer between the processing devices to further improve the power saving.

In an embodiment the means for non- volatile storage may be a hard disk drive or an optical disk drive or a flash memory device. Such drives and devices are applied in Consumer Electronics devices to provide large media collections and may contribute significantly to the power consumption of the Consumer Electronics devices.

In a further embodiment the means for communication may be a wireless Ethernet interface or a Blue tooth interface or a wireless mobile phone interface. Such communication means are also applied in Consumer Electronics devices to provide media exchange functionality and may also contribute significantly to the power consumption of the Consumer Electronics devices.

In another embodiment the non-operating mode may be a standby mode or a power-off mode. Since devices or component units may provide multiple non-operating modes with multiple power consumption levels and start-stop cycle times it is beneficial to take these into account when distributing the buffer between the processing devices.

In a further embodiment the operating mode may be read mode or a write mode. Such a mode is used prevalently in non-volatile storage drives and devices.

In another embodiment the non-operating mode may be a power-save mode or a power-off mode. Such a mode is used prevalently in wireless interfaces to provide multiple power consumption levels and start-stop cycle times. It is beneficial to take these into account when distributing the buffer between the processing devices.

In one embodiment the operating mode may be an active mode. Such a mode is used prevalently in wireless interface devices. In an embodiment the means for allocating may be a processor. Processors are commonly used in Consumer Electronics devices since they provide flexibility in the implementation of functionality.

In a further embodiment the first data rate may comprise a sum of a plurality of individual stream data rates required of the first processing unit. In situations wherein a processing unit may handle multiple streams it is sufficient to treat the multiple streams as a single stream with a total data rate equal to the sum of the data rates of the individual streams. The buffer may then be distributed without having to provide any further provisions than already disclosed. In another embodiment the second data rate may comprise a sum of a plurality of individual stream data rates required of the second processing unit. The buffer may then also be distributed without having to provide any further provisions than already disclosed. In a further embodiment a device according to the invention may be realized as at least one of the group consisting of a Set-Top-Box device, a digital video recording device, a network-enabled device, a conditional access system, a portable audio player, a portable video player, a mobile phone, a DVD player, a CD player, a hard disk based media player, an Internet radio device, a computer, a television, a public entertainment device and an MP3 player. However, these applications are only exemplary.

The data processing required according to the invention can be realized by a computer program, that is to say by software, or by using one or more special electronic optimization circuits, that is to say in hardware, or in hybrid form, that is to say by means of software components and hardware components.

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. Fig. 1 illustrates a device according to an exemplary embodiment of the invention.

Fig. 2a illustrates the processing of streams in a prior art device.

Fig. 2b illustrates the processing of streams in a device according to an exemplary embodiment of the invention. Fig. 3 illustrates a flow chart of a method according to an exemplary embodiment of the invention.

Fig. 4 illustrates an example of the variation in the power consumption versus buffer size according to an exemplary embodiment of the invention. Fig. 5 illustrates a second device for saving energy according to an exemplary embodiment of the invention.

Fig. 6 illustrates a third device for saving energy according to an exemplary embodiment of the invention. Fig. 7 illustrates a fourth device for saving energy according to an exemplary embodiment of the invention.

Fig. 8 illustrates the buffer distribution when multiple individual streams per processing device are required.

Fig. 9 illustrates an example of the variation in the power consumption versus time for a first wireless network device.

Fig. 10 illustrates an example of the variation in the power consumption versus time for a second wireless network device.

Fig. 11 illustrates an example of the variation in the power consumption versus time for a hard disk drive. The Figures are schematically drawn and not true to scale, and the identical reference numerals in different Figures refer to corresponding elements. It will be clear for those skilled in the art, that alternative but equivalent embodiments of the invention are possible without deviating from the true inventive concept, and that the scope of the invention will be limited by the claims only.

DETAILED DESCRIPTION OF THE INVENTION

In the following the term processing unit is prevalently used. The term processing unit may include a single processing step practiced on a data stream, or it may comprise multiple individual processing steps taken as one. Examples of processing units are audio/video encoders or decoders, data stream filters, audio processing for equalization, video processing for colors etc. The term processing unit may also include the process of storing a data stream. For example, in non- volatile memory, such as a hard disk drive, optical disc drive or on a flash memory device. The term processing unit may also include the process of transmitting or receiving a data stream via a network interface controller in wired or wireless configurations. In the scope of the present invention a processing unit should be understood as a unit having an input, or output, for a data stream, and that the data stream is processed in a streaming manner. For inherently non-streaming units which multiplex multiple data streams, such as hard disk drives and wireless interface cards, this may be achieved with the assistance of a streaming buffer. Fig. 1 shows a device 100 according to the invention. The device 100 comprises a means for non- volatile storage 170, which may be a hard disk drive, a floppy disc drive, a flash memory device or equivalent. The means for non- volatile storage 170 may be used to store audio and video that a user 192 would like to preserve or render. The device 100 may, for example, be a portable audio/video jukebox device running on a battery (not shown). The device 100 may also comprise a codec 150 for encoding and/or decoding audio/video data streams for display on a local display 160. An audio rendering device (not shown), such as a speaker, may also be present in the device 100. The device 100 may also comprise a means for communication 130, such as an Ethernet interface, in wired or wireless form, a WiFi interface, a Blue tooth interface or a mobile phone network interface. A network interface controller may also be understood as a means for communication 130. The device 100 may then also receive one or more data streams via the means for communication 130 for decoding using the codec 150 and further display on the local display 160 or for storing in the means for non- volatile storage 170. The means for communication 130 may also be used to transmit data streams to a remote display 165 via network 180. The network 180 may be a local network or a worldwide network such as the Internet. The user 192 may interact with the device 100 using a user interface 190. Typically, the user 192 interacts with the user interface 190 using a remote control 191, but other means of interaction are also possible. For example, the user 192 may interact with the device 100 using a touchscreen, a scroll wheel, buttons, a mouse or other pointer device, a keyboard etc.

The means for communication 130 and the means for non- volatile storage 170 generally consume significant amounts of power during operation. To reduce the power consumption a buffer 110 may be used to temporarily store data streams such that component units, such as the means for non- volatile storage 170 and the means for communication 130, may be powered down. This ensures that the data streams may still be processed and that the quality of service expected by the user 192 is preserved. For example, in Fig.l, the buffer 110 may be distributed, or split, amongst the means for non- volatile storage 170 and the means for communication 130 as a first portion 111 and a remaining portion 112 respectively. This may be achieved by the use of control program running on a processor 120 and a system bus 140. The system bus 140 may interconnect all of the component units comprised within the device 100, allowing the processor 120 to control each component unit.

In the prior art, as shown in Fig. 2a, all data streams make use of a single processing unit that dominates the power consumption during the processing of each stream, i.e. the data streams, whilst being unrelated from each other, are not fully independent in that they share the dominant power consuming processing unit. For example, in Fig. 2a, a first stream 210 is processed by the means for communication 130 and is stored on or retrieved from the means for non- volatile storage 170. In parallel, a local stream 230 is retrieved from the means for non- volatile storage 170 and is decoded by codec 150 as a decoded local stream 240 and displayed using local display 160. A multiplexed data stream 220 ensures that parallel operation of the first stream 210 and the local stream 230 is possible. In general, the means for non- volatile storage 170 is a more dominant power consumer than the means for communicating 130 and allocating the buffer 110 fully to the means for non- volatile storage 170 optimizes the total power consumption of the device 100. The buffer 110 may then be distributed amongst the first stream 210 and the local stream 230 according to the stream processing data rates. This is a characteristic of the prior art. In Fig. 2a an example is shown wherein the first stream 210 has a higher data rate than the local stream 230 and therefore receives the major portion of the buffer 110.

Given the functionality of modern Consumer Electronics devices it is, however, quite possible that configurations exist wherein the data streams to be processed do not share the processing unit which dominates the power consumption. For example, in Fig. 2b, the first stream 210 is processed as shown in Fig. 2a, but a second stream 250 also has to be processed. The second stream 250 is sourced via the means for communication 130 and is decoded by codec 150 as a decoded second stream 260 for display on local display 160. In this configuration, the first stream 210 and the second stream 250 are processed in a fully independent manner. Specifically, the second stream 250 is not processed by the means for non- volatile storage 170 at all. Allocation of the buffer 110 fully to the means for nonvolatile storage 170 would therefore not provide optimal power saving for the device as a whole. The power can still be optimized if the buffer 110 is initially distributed across the processing units according to their power consumption when independent streams are configured. For example, by distributing the buffer 110 as the first portion 111 and the second portion 112. The details of the process by which the buffer 110 is distributed will be described in more detail later in this specification.

In Fig. 5, a further example is shown of a configuration that requires that the buffer 110 be distributed across multiple processing units rather than assigned purely to the dominant power consuming processing unit. The configuration of Fig. 5 is similar to that of Fig. 2a, however, the dominant power consuming processing unit is the means for communication 130. In Fig. 5, the means for non-volatile storage 170 supplies the multiplexed data stream 220 comprising the first stream 210 and the second stream 250. The first stream 210 is decoded by codec 150 as a decoded local stream 240 for display on local display 160. The second stream 250 is transmitted, via the means for communication 130, for display on remote display 165 (not shown in Fig. 5). In this configuration, the first stream 210 and the second stream 250 are again processed in a fully independent manner, with respect to the dominant power consuming processing unit, i.e. the means for communication 130 in this configuration. Specifically, the second stream 250 is again not processed by the means for non- volatile storage 170 at all. The power can again be optimized if the buffer 110 is initially distributed across the processing units according to their power consumption when independent streams are configured. For example, by distributing the buffer 110 as the first portion 111 and the second portion 112.

In Fig. 6 a more generic embodiment according to the present invention is illustrated. The device 100 may comprise a first processing unit 610 for processing the first stream 210 and a second processing unit 620 for processing the second stream 250. The first processing unit 610 may be a means for non- volatile storage and may have first power consumption characteristics 640 whilst the second processing unit 620 may be a means for communication and may have second power consumption characteristics 650. Other processing means are also possible for the first processing unit 610 or the second processing unit 620. The details of the power consumption characteristics will be described in more detail later in this specification. A means for allocating 630 may be provided that analyses the first power consumption characteristics 640 and the second power consumption characteristics 650 and determines the distribution of the buffer 110 into the first portion 111 for use by the first processing unit 610 and the remaining portion 112 for use by the second processing unit 620. The means for allocating 630 may be embodied by the processor 120 running suitable program code. In Fig. 7 an embodiment is shown wherein the means for allocating 630 is provided with a stream characteristics input 710. The stream characteristics input 710 may receive information about the first stream 210 and the second stream 250 or, in fact, any stream to be processed by the device 100. The information may be provided as stream characteristics 720 and may be provided by an application under command of the user 192. In Fig. 7, the buffer 110 is distributed in the first portion 111 and the remaining portion 112 by taking into account the first power consumption characteristics 640, the second power consumption characteristics 650 and the stream characteristics 720. The stream characteristics 720 may also be considered as describing the requirements, for a normal quality of service, placed by the user 192 upon the device 100. The stream characteristics 720 may comprise a data rate required of the first processing unit 610 and a data rate required of the first processing unit 620. Optionally, the stream characteristics 720 may also comprise the maximum size of the buffer. This is useful when a decision is to be taken whether a component device should be powered down at all, i.e. whether energy would actually be saved given the maximum size of the buffer available. However, in some cases, a ratio indicating the buffer distribution may be enough. In these cases the maximum buffer size is not explicitly required.

In Fig. 3 a flowchart is illustrated which may be implemented upon the processor 120 of Fig. 1. A number of steps, namely steps 300, 310 and 320, may be completed in parallel, as is shown in Fig. 3, or in a sequential order (not shown in Fig. 3). In step 300, the first power consumption characteristics 640 are determined for the first processing unit 610. These may be measured, loaded from a memory, requested from the first processing unit 610 or obtained in any suitable manner. In step 310, the second power consumption characteristics 650 are determined for the second processing unit 620. This may be performed in a similar manner as that for the first processing device 610. Optionally, the stream characteristics 720 may also be supplied, for example, via an application using a suitable application programming interface, or API. In step 330, the buffer 110 is distributed into the first portion 111 and the remaining portion 112 by calculating the optimal buffer distribution. In a final step 340 the streams are started and are streamed into, or from, the respective portion of the buffer 110 to, or from, the respective processing unit. The calculation of the buffer distribution will now be disclosed in detail.

In the following the details of the process by which the buffer 110 is distributed will be described. Firstly, the power consumption characteristics of a number of typical processing units will be described. Thereafter, a model will be disclosed by which the processing units may be collectively modeled. Finally, it will be disclosed how the optimal buffer distribution may be determined.

In Fig. 11, a power consumption trace is illustrated for a hard disk drive. The horizontal axis 1100 of Fig. 11 is time in seconds. The vertical axis 1110 of Fig. 11 is power in Watts. The trace illustrated in Fig. 11 begins with the hard disk drive in standby mode 1120. This is the lowest power mode of all those illustrated in Fig. 11. Powering off the hard disk drive completely could save power further (this is not shown in Fig. 11). Upon receiving a command the hard disk drive may enter a load mode 1130. Generally this involves spinning the disk(s) inside the hard disk drive to normal operating speed and placing the read/write head in the data area of the disk. This may involve a mere seek action from a so-called landing zone or by unloading the read/write head from a ramp. A command may be executed in a read/write mode 1140. Generally a hard disk drive will remain in a performance idle mode 1150, where the hard disk drive waits for a certain period of time for further commands. In this mode the hard disk drive may respond immediately to the commands. In an active idle mode 1160 the hard disk drive may power down as much of the periphery components as possible. For example, it may stop active track following, shut down read/write channel electronics etc. If no further commands are received, the hard disk drive may unload the read/write head. This is typically performed in ramp load hard disk drives used in mobile or portable applications. The unload mode 1170 involves moving the read/write to the ramp. This reduces power consumption in a low power idle mode 1180 since the read/write head is no longer flying in close proximity to the disk surface and the "drag" is reduced. The spindle may also be run at a lower speed than normal operation and further periphery electronics may be disabled. The trace illustrated in Fig. 11 also indicates the duration required to perform a power mode transition. For example, the duration of the load mode 1130 is the duration required to transition from standby mode 1120 to read/write mode 1140.

The power consumption of the hard disk drive in the various power modes and the transitions durations between such power modes may be modeled. For example, the average power consumption of the hard disk drive during streaming via a stream buffer where the disk is spun up to refill the buffer only when the buffer filling drops below a predetermined level is equal to

where r is the bit rate of the stream, r_</ the data rate of the disk, t_sud and E_SU(j the time and energy required to spin up and spin down the disk once, P_r disk read or write power consumption depending upon the situation, P_sb the standby power consumption of the disk and b the buffer size. The first power consumption characteristics 640 may comprise one or more of these parameters. In Fig. 9 a power consumption trace is illustrated for a first wireless interface card. The horizontal axis 900 of Fig. 9 is time in seconds. The vertical axis 910 of Fig. 9 is power in Watts. The trace illustrated in Fig. 9 begins with the first wireless interface card in power-off mode 920. To reduce further any power drain by the mere interfacing of the first wireless card to a host, the first wireless card may be fully isolated using, for example field effect transistors, i.e. FETs, or other suitable means. After a period of time in power off mode 920 the first wireless card transitions to an active mode 930. Thereafter, the first wireless card transitions to a power save mode 940. This is generally under control of firmware within the first wireless card, or under control of a host system. Signals may be intermittently transmitted and/or received in the power save mode 940. If necessary, the first wireless card may transition again to the active mode 930. Typical measured values for the power consumption and the power mode transition durations of the first wireless card are shown in Table 1. The second power consumption characteristics 650 may comprise one or more of the parameters shown in Table 1.

Table 1 Power consumption and mode cycle times of a first wireless interface device measured using a 100 ms beacon interval. AM is Active mode, PS is Power Save mode.

In Fig. 10 a power consumption trace is illustrated for a second wireless interface card. The horizontal axis 1000 of Fig. 10 is time in seconds. The vertical axis 1010 of Fig. 10 is power in milliwatts. The trace illustrated in Fig. 10 begins with the second wireless interface card in active mode 930. After a period of time in active mode 930 the second wireless card transitions to a power save mode 940. Again, this is generally under control of firmware within the second wireless card, or under control of a host system. Signals may be intermittently transmitted and/or received in the power save mode 940. Such signals may be beacon signals transmitted at a beacon interval 1020. Typical measured values for the power consumption of the second wireless card are shown in Table 2. The second power consumption characteristics 650 may comprise one or more of the parameters shown in Table 2.

Table 2 Power consumption of a second wireless interface device ^measured using a 100 ms beacon interval. AM is Active mode, PS is Power Save mode.

The measurements shown in Table 2 are a worst-case situation. During a data transfer using a commonly used protocol, such as TCP/IP, the average transmit power consumption will be lower. As an example, from power up until ready it was measured that 14OmJ of energy was consumed during 2.3 seconds.

It is possible to apply a similar power consumption model to a wireless interface card as applied to the hard disk drive above. For example, the average power consumption of a wireless network interface card during streaming via the same buffering scheme as for the hard disk drive, equals

where r_w is the effective data rate of the wireless network interface card, t_ps._am and E_ps._am are the time and energy consumption to transition from the power save mode (ps) 940 to the active mode (am) 930 and back to the power save mode 940, P_rx the receive or transmit power consumption depending upon the situation and P_ps the power save mode 940 power consumption. Again, the second power consumption characteristics 650 may comprise one or more of these parameters.

The average power consumption of the hard disk drive of Fig. 11 and wireless network cards of Fig. 9 or Fig. 10 decreases with increasing buffer size and for very large buffers converges to

P_r r/r_d + P_sb (1 - r/r_d) and P_n r/r_w + P_ps (1 - r/r_w) respectively.

For the configuration illustrated in Fig. 2b and described in detail in the text accompanying Fig. 2b above, the total power consumption would be P_mal = PJr_l,b) + P_hdd(r_l,b) + P_w(r₂,b_total -b) (3) where rj is the bit rate of the stream being recorded, T2 the bit rate of the stream being played, b the stream buffer size for recording and b_totai is the total buffer size available for all streams.

The stream characteristics 720 may comprise one or more of these parameters. The size of the buffer for the playback stream equals b_totai - b. Such a configuration could describe a situation wherein the first stream 210 was recorded from the means for communication 130 to the means for non- volatile storage 170, whilst receiving the second stream 250 wirelessly for playback on the local display 160.

Since the average power consumption of both the means for non-volatile storage 170 and the means for communication 130 decreases with increasing stream buffer size and they both share the total available buffer memory, there is an optimal split of the buffer memory that minimizes the total power consumption of the means for non- volatile storage 170 and the means for communication 130. That optimum can be found by finding the roots of the first derivative of equation (3).

^-P_total = ^PM,b) + ^P_hdd(r_ι,b) + j-P_w(r₂A_otal -b) = 0 (4) ab ab ab ab with

Equation (4) has only one root that is smaller that b_totai- ^ri^r _W Ol - ^rd )(^Esud ^~ Kud^P _Sb ) + ^rΛ Ol - OiEps-am ^~ t_pS-am^P _pS ) + ^{• • •}

The "..." notation, appearing twice in Equation (8), should be read as merely a continuation of the line and has no mathematical meaning. Usually t_sudP_sb « E_SU(t and t_ps-_amPps « E_ps._am- This assumption leads to a simpler optimal buffer size b_opt,i- ψ_W Oi - ^rd )^Esud + Ψd (i - ^rw )^Eps-_am + ^{• • •} 4^rWd (^r2 ^{~ r}w )^E ps-am ^ fø ^{~ T}d )^E sud + ^Vd Ol ^~ ^w )^-_am ) ψΛn -^rd)^Esud +^rd(n(n -r_w) -Φ₂ -rj)E_ps__am

The "..." notation, appearing once in Equation (9), should again be read as merely a continuation of the line and has no mathematical meaning. Also the influence oϊP_w(ri,b) on the optimal buffer size is negligible. Removing P_w(ri,b) from equation (4) leads to the optimal buffer size b_opt, 2- ψ_W (i - ^rd )(^Esud - Kud^Psb ) + ^{■ ■ ■}

The "..." notation, appearing once in Equation (10), should again be read as merely a continuation of the line and has no mathematical meaning. Removing P_w(ri,b) from equation (4) and neglecting t_sudP_sb and t_ps._amP_Ps since t_sudP_sb « E_sud and t_ps._amPps « E_ps._am leads to the optimal buffer size b_opt,3-

Therefore, the optimal buffer distribution between the first portion 111 and the remaining portion 112 may be calculated according to b_opt, b_opt,i, b_opt,2, b_opt,3 or any derivative thereof.

Fig. 4 shows an example plot of the total power consumption versus the buffer size for a situation wherein the following parameters were used: r;=2Mb/s, r2=2Mb/s,

r_w=5.4Mb/s, P^=O.16W, t_ps._am=OA Is and P«=1W. In Fig. 4 the horizontal axis 400 is the buffer size in megabytes and the vertical axis 410 is power in Watts.

Fig. 4 shows the total power consumption, P_totø/450, the power consumed, Phodfri.b) 420, by the means for non- volatile storage 170, the power consumed, P_w(ri,b) 430, by the means for communication 130 for the first stream 210 and the power consumed, P_w(r2,b_totai-b) 440, by the means for communication 130 for the second stream 250. The two circles are the roots of 3Ptotai/3b. One of the roots, root 470, of dP_totai/db is larger than b_totai and not useful. The other root, root 460, is an optimal buffer size for b. The ratio b to b_totai gives the optimal buffer distribution. The power consumption of the buffer itself may also be taken into account in the determination of the optimal buffer distribution.

In configurations wherein the first processing unit 610 and/or the second processing unit 620 are required to support multiple streams in a streaming manner, it may be preferable to split the available buffer space between the first processing unit 610 and the second processing unit 620 before splitting the buffer space amongst the individual streams themselves. For example, in Fig. 8 a configuration is shown wherein the first processing unit 610 must process three streams. The three streams each have an associated data rate, namely a first data rate 810, a second data rate 820 and a third data rate 830. In Fig. 8 the second processing unit 620 must stream two streams. These two streams also each have an associated data rate, namely a fourth data rate 850 and a fifth data rate 860. In distributing the buffer 110 amongst the first processing unit 610 and the second processing unit 620 a first summed data rate 840 is calculated from the sum of the first data rate 810, the second data rate 820 and the third data rate 830. Also a second summed data rate 870 is calculated from the sum of the fourth data rate 850 and the fifth data rate 860. The first summed data rate 840 and the second summed data rate 870 are used as the applicable data rates in the calculation of the buffer distribution of the first portion 111 and the remaining portion 112, for example, as ri and T2 respectively in equation (3).

In summary the invention discloses methods and devices for saving energy by sharing a buffer. The device 100 may comprise at least a first processing unit 610 for processing a first stream 210 and a second processing unit 620 for processing a second stream 250 wherein the first processing unit 610 and the second processing unit 620 process the first stream 210 and the second stream 250 independently from each other. A buffer 110 for common use by the first processing unit 610 and the second processing unit 620 is optimally distributed into a first portion 111 and a remaining portion 112 for the first processing unit 610 and the second processing unit 620 respectively. The buffer 110 is distributed by a means for allocation 630 based upon first power consumption characteristics 640 of the first processing unit 610 and second power consumption characteristics 650 of the second processing unit 620. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. Furthermore, any of the embodiments described comprise implicit features, such as, an internal current supply, for example, a battery or an accumulator. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice- versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A device (100) for saving energy by sharing a buffer, the device comprising: the buffer (110), the buffer comprising at least a first portion (111) and a remaining portion (112); a first processing unit (610) for processing a first stream (210), the first processing unit having first power consumption characteristics (640); a second processing unit (620) for processing a second stream (250), the second processing unit having second power consumption characteristics (650); and a means for allocating (630) the first portion to the first processing unit and the remaining portion to the second processing unit characterized in that the device is adapted to process the first stream and the second stream independently; and the means for allocating are adapted to allocate the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.

2. The device of claim 1 wherein the first processing unit is a means for nonvolatile storage (170).

3. The device of claim 1 wherein the second processing unit is a means for communication (130).

4. The device of claim 1 wherein the means for allocating is further adapted to allocate the first portion and the remaining portion based further upon the processing rate of the first stream and the processing rate of the second stream.

5. The device of claim 1 wherein the means for allocating further comprises a stream characteristics input (710); and wherein the means for allocating is further adapted to allocate the first portion and the remaining portion based further upon stream characteristics (720) received from the stream characteristics input.

6. The device of claim 1 wherein first power consumption characteristics comprise at least one of the group consisting of: a data rate; a non-operating power consumption in a non-operating mode; an operating power consumption in an operating mode; a cycle time period required to transition from the operating mode to the non- operating mode; a cycle energy usage required to transition from the operating mode to the non-operating mode.

7. The device of claim 1 wherein second power consumption characteristics comprise at least one of the group consisting of: a data rate; a non-operating power consumption in a non-operating mode; an operating power consumption in an operating mode; a cycle time period required to transition from the operating mode to the non- operating mode; a cycle energy usage required to transition from the operating mode to the non-operating mode.

8. The device of claim 5 wherein the stream characteristics input comprises: a first data rate required of the first processing unit; a second data rate required of the second processing unit; and a maximum size of the buffer.

9. The device of claim 6 wherein the means for non- volatile storage is a hard disk drive or an optical disk drive or a flash memory device.

10. The device of claim 7 wherein the means for communication is a wireless Ethernet interface or a Blue tooth interface or a wireless mobile phone interface.

11. The device of claim 9 wherein the non-operating mode is a standby mode (1120) or a power-off mode.

12. The device of claim 9 wherein the operating mode is read mode or a write mode (1140).

13. The device of claim 10 wherein the non-operating mode is a power-save mode (940) or a power-off mode (920).

14. The device of claim 10 wherein the operating mode is an active mode (930).

15. The device of claim 1 wherein the means for allocating is a processor (120).

16. The device of claim 8 wherein the first data rate (840) comprises a sum of a plurality of individual stream data rates (810, 820, 830) required of the first processing unit.

17. The device of claim 8 wherein the second data rate (870) comprises a sum of a plurality of individual stream data rates (850, 860) required of the second processing unit.

18. The device of claim 1 realized as at least one of the group consisting of: a Set-Top-Box device; a digital video recording device; a network-enabled device; a conditional access system; a portable audio player; a portable video player; a mobile phone; a DVD player; a CD player; a hard disk based media player; an Internet radio device; a computer; a television; a public entertainment device; and an MP3 player.

19. A method for saving energy by sharing a buffer, the method comprising the steps of: determining (300) first power consumption characteristics (640) of a first processing unit (610); determining (310) second power consumption characteristics (650) of a second processing unit (620); and allocating (330) a first portion (111) of the buffer (110) to the first processing unit and the remaining portion (112) of the buffer to the second processing unit characterized in that the first processing unit and the second processing unit process streams independently; and the step of allocating further allocates the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.

20. The method of claim 19 wherein the first processing unit is a means for non- volatile storage (170).

21. The method of claim 19 wherein the second processing unit is a means for communication (130).

22. The method of claim 19 wherein the method further comprises the method steps of: receiving (320) stream characteristics (720); and wherein the step of allocating allocates the first portion and the remaining portion based further upon the stream characteristics.

23. The method of claim 19 wherein first power consumption characteristics comprise at least one of the group consisting of: a data rate; a non-operating power consumption in a non-operating mode; an operating power consumption in an operating mode; a cycle time period required to transition from the operating mode to the non- operating mode; a cycle energy usage required to transition from the operating mode to the non-operating mode.

24. The method of claim 19 wherein second power consumption characteristics comprise at least one of the group consisting of: a data rate; a non-operating power consumption in a non-operating mode; an operating power consumption in an operating mode; a cycle time period required to transition from the operating mode to the non- operating mode; a cycle energy usage required to transition from the operating mode to the non-operating mode.

25. The method of claim 22 wherein the stream characteristics comprise: a first data rate required of the first processing unit; a second data rate required of the second processing unit; and a maximum size of the buffer.

26. A program element directly loadable into the memory of a programmable device, comprising software code portions for performing, when said program element is run on the device, the method steps of: determining (300) first power consumption characteristics (640) of a first processing unit (610); determining (310) second power consumption characteristics (650) of a second processing unit (620); and allocating (330) a first portion (111) of a buffer (110) to the first processing unit and the remaining portion (112) of the buffer to the second processing unit characterized in that the first processing unit and the second processing unit process streams independently; and the step of allocating further allocates the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.

27. A computer-readable medium directly loadable into the memory of a programmable device, comprising software code portions for performing, when said code portions are run on the device, the method steps of: determining (300) first power consumption characteristics (640) of a first processing unit (610); determining (310) second power consumption characteristics (650) of a second processing unit (620); and allocating (330) a first portion (111) of a buffer (110) to the first processing unit and the remaining portion (112) of the buffer to the second processing unit characterized in that the first processing unit and the second processing unit process streams independently; and the step of allocating further allocates the first portion and the remaining portion based upon the first power consumption characteristics and the second power consumption characteristics.