WO2006003539A1

WO2006003539A1 - Method and circuit for buffering a stream of data

Info

Publication number: WO2006003539A1
Application number: PCT/IB2005/051982
Authority: WO
Inventors: 0Zcan Mesut; Johannes Henricus Maria Korst; Jozef Pieter Van Gassel; John Hamers
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-06-29
Filing date: 2005-06-15
Publication date: 2006-01-12
Also published as: CN1977233A; KR20070027626A; EP1784708A1; JP2008504641A; TW200622574A

Abstract

Energy still is a precious commodity for portable consumer devices. In such devices, data is usually read from a mass storage device like a harddisk, buffered in a solid state memory and then rendered (processed) for reproduction over usually headphones (and a screen when applicable). The invention is aimed at more efficient use of the buffer memory, which is usually divided in compartments. The invention is based on the recognition that individual compartments of a (e.g.) dynamic buffer memory should be emptied as fast as possible as compared to gradually reading data from various compartments of the memory. In this way, considerable amounts of energy can be saved as an inactive memory compartment consumes less power than an active memory compartment.

Description

Method and circuit for buffering a stream of data

The invention relates to a method for buffering a first stream of audiovisual data and a second stream of audiovisual data in a buffer memory comprising at least two compartments.

The invention also relates to a method of buffering a stream of data in a buffer memory comprising at least two compartments.

The invention further relates to a circuit for buffering a first stream of audiovisual data and a second stream of audiovisual data in a buffer memory comprising at least two compartments.

The invention relates to a circuit for buffering a stream of data in a buffer memory comprising at least two compartments as well.

The invention also relates to a computer programme product comprising computer readable and executable instructions.

The invention further relates to a medium carrying such computer programme product.

With the downsizing and capacity increase of memory products like harddisk drives and Flash EEPROM ICs, currently a large variety of portable music and video players are available today. Although technology has made some advantages over the recent years, energy consumption is still a major issue for such devices. Especially devices that have a harddisk drive as mass storage device consume a lot of power. Several proposals for saving power for such devices have been proposed in the past, for example in WO 2004/023279, but there is still a need for improvement.

Therefore, it is an object of the invention to provide a more efficient method of buffering data when retrieved. To achieve this object, the invention provides in a first aspect a method of buffering a first stream of audiovisual data and a second stream of audiovisual data in a buffer memory comprising at least two compartments, comprising the steps of : writing at least part of the first stream and the second stream interleaved in the buffer memory, such that each compartment of the memory comprises data of the first stream of audiovisual data and the second stream of audiovisual data; and retrieving the data stored in the buffer memory for retrieval for further processing. A person skilled in the art would allocate a first part of the memory for storing data for buffering the first stream and a second part of the buffer memory for buffering the second stream. In this case, the data of the first stream would be in a first set of compartments and the data of the second stream would be in a complementary set of compartments. This would mean that most of the memory would be active and that it is quite likely that data would have to be read from two compartments. In an active state of a compartment, i.e. read and/or write state, a memory compartment consumes considerably more energy than in an inactive state, i.e. refresh or standby (no refresh, so no data preservation).

By applying this method according to the invention, the number of compartments in active state is reduced. Because both streams of data are stored interleaved, at least in first instance only one memory compartment will be active, as data from both streams to process is located in the same memory compartment. Only this compartment has to be active; the other compartments are in an inactive state.

In an embodiment of the invention, the method further comprises the steps of: determining a first data rate at which the first stream is being processed after retrieval; determining a second data rate at which the second stream is being processed after retrieval; writing a first amount of data of the first stream in the buffer memory; and writing a second amount of data of the second stream in the buffer memory; such that the ratio of the first amount and the second amount equals the ratio of the first data rate and the second data rate. In this way, the buffer is empty with respect to the first stream as well as the second stream. This means that in case the data of both streams is stored on a harddisk, data of both stream can be retrieved from the harddisk in one reading session. In other cases, each stream would need a separate reading session. This is not efficient from an energy consumption point of view, as preferably, the harddisk is in a mode with less power consumption between the read sessions and it costs a considerable amount of energy to go to the active reading mode of the harddisk. Furthermore, when the data is stored interleaved, the compartments are emptied one by one. This may not be exactly the case when the streams have a variable bitrate for processing, but on average, only one compartment of the buffer memory will be active. A second aspect of the invention provides a method of buffering a stream of data in a buffer memory comprising at least two compartments, comprising the steps of: writing the data sequentially in a buffer memory comprising at least a first compartment and a second compartment; retrieving the data from the buffer memory for further processing; and when data stored in the first compartment has been fully retrieved for further processing, switching the first compartment to a low power mode.

When only one stream is buffered, only one compartment of the buffer memory is active. The advantage of this aspect of the invention is that it is known that data will not be used anymore, directly after it has been read. When data is read in a rather random way over the memory and it is not certain whether and/or when it will have to be read again (like for example in a PC), a compartment of which all data has been read cannot be just switched off. First, depending on the nature of the low power mode (only refresh or no refresh at all), data might be lost. Second, going from a low power state to an active state costs time. US 6141283 proposes to monitor memory banks of an SDRAM and switch them to an idle state when those banks are not being accessed. In the application disclosed by this patent publication, however, the memory is not being used as a buffer and even in the idle state, the contents of the memory have to be preserved. This means that also in the idle state, the memory has to be fed with energy to refresh the data in the DRAM memory. This is not the case when a DRAM memory is used as a buffer. The reason for this is that data does only have to be read once. After the data has been read, no energy has to be spent on a refresh operation anymore.

Therefore, in an embodiment of the second aspect of the invention, the buffer memory is a dynamic memory and the low power mode is a mode wherein the memory is not refreshed anymore. In this way, a considerable amount of extra energy can be saved compared to the state of the art.

The first and second aspects of the invention rely on one single inventive concept, which is the recognition that individual compartments of a (e.g.) dynamic buffer memory should be emptied as fast as possible as compared to gradually reading data from various compartments of the memory. In this way, considerable amounts of energy can be saved as an inactive memory compartment consumes less power than an active memory compartment. It will be apparent to a person skilled in the art that the embodiments of the first aspect as claimed in dependent claims can be applied to the second aspect and vice versa. A third aspect of the invention provides a circuit for buffering a first stream of audiovisual data and a second stream of audiovisual data in a buffer memory comprising at least two compartments, comprising: a buffer memory comprising at least two compartments; and a central processing unit conceived to control the buffer memory to: write at least part of the first stream and the second stream interleaved in the buffer memory, such that each compartment of the memory comprises data of the first stream of audiovisual data and the second stream of audiovisual data; and retrieve the data stored in the buffer memory for retrieval for further processing.

A fourth aspect of the invention provides a circuit for buffering a stream of data in a buffer memory comprising at least two compartments a buffer memory comprising at least two compartments; and a central processing unit conceived to control the buffer memory to: write the data sequentially in a buffer memory comprising at least a first compartment and a second compartment; retrieve the data from the buffer memory for further processing; and when data stored in the first compartment has been fully retrieved for further processing, switch the first compartment to a low power mode.

A fifth aspect of the invention provides a computer programme product comprising computer readable and executable instructions to let a computer execute the method according to claim 1.

A sixth aspect of the invention provides a computer programme product comprising computer readable and executable instructions to let a computer execute the method according to claim 9.

Unpublished application WO IB2004/050091 also proposes a method of reducing power consumption in - for example - portable devices.

The embodiments of the invention will be elucidated by means of Drawings. In these drawings:

Figure 1 shows an embodiment of the apparatus according to the invention comprising an embodiment of the circuit according to the invention and an embodiment of the medium according to the invention;

Figure 2 shows a more detailed drawing of the buffer memory; and Figure 3 shows a more detailed drawing of the buffer memory comprising data for two streams of data. Figure 1 shows a portable audio player 100 as an embodiment of the apparatus according to the invention, comprising a harddisk drive 102 as a storage device, a rendering unit 104, user input means 106 and a circuit 110 as an embodiment of the circuit according to the invention, the circuit 110 comprising a buffer memory 114, a central processing unit 112 and a ROM memory 116 as an embodiment of the record carrier according to the invention.

A user can put audio data on the harddisk 102 via a PC link (not shown). When a user selects an audio track to be played over headphones 150 by means of the user input means 106, audio data is read from the harddisk 102, written into the buffer memory 114, read from the buffer memory 114 and processed by the rendering unit 104 for reproduction by the headphones 150. These operations are controlled by the central processing unit 112, which is programmed by a computer programme stored in the ROM memory 110. In another embodiment of the invention, the central processing unit is an ASIC (Application Specific Integrated Circuit), dedicated for performing the embodiment of the method according to the invention without the need of being programmed.

The audio data is not directly sent from the harddisk drive 102 to the rendering unit 104 for several reasons. The most important reason is that data rates should be matched. The bandwidth of data retrieval from a (small, 1 inch) harddisk is in the order of tens of megabits per second (for larger drives, it is over a hundred megabits per second), whereas the rendering unit renders audio tracks at a much lower bandwidth, which is for MP3 compressed audio usually 128 kilobits per second. Another reason for buffering is reduction of power consumption of the total portable audio player 100. A harddisk drive is known to consume a lot of power when the disc is kept spinning. Therefore, it is advantageous to buffer data read from a harddisk drive in a memory that consumes less power and put the harddisk drive in low power mode or even shut it off. The buffer memory can be implemented in for example an SRAM or a DRAM memory. More details to this principle can be found in publication WO 2004/023279-A2, application WO IB2003/006342, application WO IB2004/000016 and application EP 03104522.2.

Even more power can be saved when the buffer memory 114 is built up from several memory banks that can be controlled separately. This is elucidated by means of Figure 2, Table 1 and Table 2. Table 1 provides data on power dissipation of 128Mb SDRAM (Synchronous Dynamic Random Access Memory) of Micron in various states that can be controlled. In the Standby mode, the memory is empty and no data is kept. In the Refresh mode, data read into the memory is kept. In the Read mode, data is read from the memory. In the Write mode, data is written to the memory. In the Read & Write mode, data can be read from and written to the memory.

State Operating Mode Power Consumption of Micron SDRAM

Mobile SDRAM Normal SDRAM

SB Standby 1.2 mW 6.6 mW

RF Refresh 6.9 mW 9.I mW

R Read 7.7 mW 10.4 mW

W Write 18.5 mW 28.7 mW

RW Read & Write 19.3 mW 30.1 mW

Table 1

Phase Time Slot Bank l Bank 2 Bank 3 Bank 4

1 0.00 - 1.34 RW SB SB SB

2 1.34 - 2.68 R W SB SB

3 2.68 - 4.03 R RF W SB

4 4.03 - 5.37 R RF RF W

5 5.37 - 33.55 R RF RF RF

6 33.55 - 67.11 SB R RF RF

7 67.11 - 100.66 SB SB R RF

8 100.66 SB SB SB R

134.22

Table 2

In Phase 1 (Table 2), data is read from the harddisk drive 102 and written to a first memory bank 202. The other banks are set on standby, to minimize the power consumption while no data is stored in those banks. In Phase 1, data is also read from the first bank 202 of the buffer memory 114. In Phase 2, the process of reading data from the first bank 202 continues and data is being written to a second memory bank 204 of the buffer memory 114.

This process continues until a third memory bank 206 and a fourth memory bank 208 have been filled. A lot of energy is saved by setting a memory bank to refresh when a memory bank has been filled and setting the memory bank to 'standby' when all data has been read for processing by the rendering unit 104.

This embodiment yields an energy saving of 10% when using normal SDRAM and even 30% when using mobile SDRAM using the method according to the invention. The method according to the invention can be used handling multiple streams as well, in an embodiment that will be described by means of Figure 3. In this embodiment, data from a first stream and a second stream are stored interleaved. The four memory banks of the buffer memory 114 are filled with first data of the first stream (diagonal stripes) and second data of the second stream (vertical stripes). Data handling of the two streams will be done with time division multiplexing, so while data of both streams is read from the first memory bank 202, the other memory banks can be kept in standby or refresh mode, saving energy.

To properly fill the four memory banks of the buffer memory 114 according to this embodiment of the invention, the data rates at which both streams are being processed by the rendering unit 104 should be known. When both streams have a continuous data rate, this is no problem. However, more and more compression algorithms apply variable bit rate compression, like MPEG2, MPEG4 and variable bit rate MP3 (MPEG 1, layer 3 audio compression). In these cases, the bit rate of the stream of audiovisual data has to be averaged. Several methods for performing this are known by the person skilled in the art, so no further details will be given in this description.

The embodiment described above is especially well suited for portable server applications.

To achieve good energy saving, the ratio between the amounts of data stored in the buffer memory 114 of each stream of data equals the ratio of bandwidth of retrieval from the buffer memory 114, which is usually equal to the bandwidth of data processing by the rendering unit 104. In this way, no further data will be retrieved from the harddisk drive 102 until the buffer memory 114 is empty (or preferably until it is nearly empty). This means that the harddisk drive 102 - preferably powered off or in standby mode when no data is read from it - is used as less as possible. This saves a considerable amount of power. When several streams are processed by the portable audio player 100, even more energy can be saved by making the ratio between the amounts of data of each stream stored in each memory bank of the buffer memory 114 equal to the ratio of bandwidth of retrieval from the buffer memory 114. In this way, the memory banks are emptied one by one, so they can be switched to 'standby' one by one. The memory banks can be embodied as separate ICs, but also memory ICs in which the status of the internal banks can be controlled separately can be used to embody the invention as well and are commercially available. When the invention is embodied using separate ICs, also the clock frequency of the banks of the buffer memory 114 can be controlled. It is well known in the art that the power consumption of ICs increases with the clock frequency of the ICs.

The maximum read/write speed used by the buffer is determined by the maximum speed of the storage medium (during writing) and the rate at which the rendering unit 104 processes the data. These frequencies are lower than the processing speed of the central processing unit 112. The data retrieval rate of an exemplary (1-inch) harddisk drive is 36 Mb-s^"1, which is 4,5 MB-s^"1 at the transfer of one byte per clock cycle. This requires a clock speed of 4,5 MHz for parallel data transfer from the harddisk drive to the buffer. The other components of the portable audio player, however, operate at a higher clock frequency. Decreasing the operating clock frequency of the memory instead of using the (general) system clock may therefore result in a power saving as well.

As mentioned before, the invention may also be embodied in a computer programme to programme a central processing unit. This computer programme can be stored in a ROM IC, but also on a magnetic medium like a harddisk, an optical medium as a CD- ROM or DVD-ROM, or an opto-magnetic medium. Embodiments of the invention have been described in cases where data is being retrieved from a local storage device like a harddisk drive. However, data may just as well be derived from a remote storage device, over a wired or wireless link. This is irrelevant for the scope of the invention.

Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in Figure 1, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

In summary, the invention relates to the following: Energy still is a precious commodity for portable consumer devices. In such devices, data is usually read from a mass storage device like a harddisk, buffered in a solid state memory and then rendered (processed) for reproduction over usually headphones (and a screen when applicable). The invention is aimed at more efficient use of the buffer memory, which is usually divided in compartments. The invention is based on the recognition that individual compartments of a (e.g.) dynamic buffer memory should be emptied as fast as possible as compared to gradually reading data from various compartments of the memory. In this way, considerable amounts of energy can be saved as an inactive memory compartment consumes less power than an active memory compartment.

Claims

CLAIMS:

1. Method of buffering a first stream of audiovisual data and a second stream of audiovisual data in a buffer memory (114) comprising at least two compartments (202, 204, 204, 206, 208), comprising the steps of : a) writing at least part of the first stream and the second stream interleaved in the buffer memory, such that each compartment of the memory comprises data of the first stream of audiovisual data and the second stream of audiovisual data; and b) retrieving the data stored in the buffer memory for retrieval for further processing.

2. Method as claimed in claim 1, wherein the data has been stored sequentially in the compartments of the buffer memory.

3. Method as claimed in claim 1 or 2, wherein the each compartment of the buffer memory can be switched off separately.

4. Method as claimed in claim 3, further comprising the step of switching off a memory bank when all data stored in said memory bank has been retrieved for further processing.

5. Method as claimed in claim 1, wherein the method further comprises the steps of: a) determining a first data rate at which the first stream is being processed after retrieval; b) determining a second data rate at which the second stream is being processed after retrieval; c) writing a first amount of data of the first stream in the buffer memory; and d) writing a second amount of data of the second stream in the buffer memory; such that the ratio of the first amount and the second amount equals the ration of the first data rate and the second data rate.

6. Method as claimed in claim 5, wherein each compartment of the buffer comprises data of the first stream and the second stream.

7. Method as claimed in claim 1, wherein the buffer memory is working at a first clock frequency that is independent from the a second clock frequency at which other circuits are working, the other circuits being comprised by an apparatus comprising the buffer memory.

8. Method as claimed in claim 7, wherein the clock frequency during presenting data same as streaming rate of stream.

9. Method of buffering a stream of data in a buffer memory (114) comprising at least two compartments (202, 204, 206, 208), comprising the steps of: a) writing the data sequentially in a buffer memory comprising at least a first compartment and a second compartment; b) retrieving the data from the buffer memory for further processing; and c) when data stored in the first compartment has been fully retrieved for further processing, switching the first compartment to a low power mode.

10. Method according to claim 9, wherein the buffer memory is a dynamic memory and the low power mode is a mode wherein the memory is not refreshed anymore.

11. Circuit (110) for buffering a first stream of audiovisual data and a second stream of audiovisual data in a buffer memory comprising at least two compartments(202, 204, 206, 208), comprising: a) a buffer memory (114) comprising at least two compartments (202, 204, 206, 208); and b) a central processing unit (112) conceived to control the buffer memory to: i) write at least part of the first stream and the second stream interleaved in the buffer memory, such that each compartment of the memory comprises data of the first stream of audiovisual data and the second stream of audiovisual data; and ii) retrieve the data stored in the buffer memory for retrieval for further processing.

12. Circuit (110) for buffering a stream of data in a buffer memory (114) comprising at least two compartments (202, 204, 206, 208) a) a buffer memory comprising at least two compartments(202, 204, 206, 208); and b) a central processing unit conceived to control the buffer memory to: i) write the data sequentially in a buffer memory comprising at least a first compartment and a second compartment; ii) retrieve the data from the buffer memory for further processing; and iii) when data stored in the first compartment has been fully retrieved for further processing, switch the first compartment to a low power mode.

13. Apparatus (100) for reproduction of audiovisual data, comprising: a) a mass storage device (102); b) a rendering unit (104) for rendering the audiovisual data; and c) the circuit according to claims 11 or 12 for buffering data transport from the mass storage device to the rendering unit.

14. Computer programme product comprising computer readable and executable instructions to let a computer execute the method according to claim 1.

15. Medium (116) carrying the computer programme product according to claim

14.

16. Computer programme product comprising computer readable and executable instructions to let a computer execute the method according to claim 9.

17. Medium (116) carrying the computer programme product according to claim 16.