Abstract:
A low-power digital audio decoding and playing system and method for computing devices provides a low-cost, low power-consumption, long-battery-life audio playing and decoding system, which may be used to play compressed audio files of various formats. In one aspect, a computer system adapted to play audio files comprises a system CPU, memory, at least one drive comprising compressed audio data, and an audio controller coupled to the system CPU, memory and drive. The audio controller is adapted to cause the drive to read the compressed audio data from the drive, to cause the system CPU to decompress the compressed audio data from the drive into decompressed audio data, to cause the decompressed audio to be stored in the memory, and to cause the decompressed audio data to be retrieved from the memory for playing.

Description:
This application claims the benefit of provisional application serial No. 60/250,899, filed on Dec. 1, 2000, entitled “Low Power Digital Audio Decoding System for Computing Devices” and provisional application serial No. 60/265,466, filed on Jan. 30, 2001, entitled “Low Power Digital Audio Decoding/Play System for Computing Devices”. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to portable devices (e.g., notebook computers) for reproducing audio recordings, and more particularly, to low-power hardware and software for decoding and reproducing compressed audio recordings in a variety of compression formats from a variety of sources. While particular utility for the present application is in the reproduction of MP3 digital audio files, especially for use with portable computers, other utilities are contemplated herein. 
   2. Description of Related Art 
   Presently there exist various portable devices for replaying digital audio recordings that have been compressed in accordance with one or more compressed audio digital recording formats, e.g., MPEG (Moving Picture Experts Group) Audio Layer-3 (MP3), Windows® Media Audio (WMA), and Advanced Audio Coding (AAC). To date, the most popular format has been MP3, a compression scheme that results in about a 10:1 compression of the size of digital music files. These devices can be divided into two classes, those which store the compressed digital audio recordings in an electronic solid-state memory, and those which record the compressed digital audio for subsequent reproduction using an electromechanical device such as a compact disk (“CD”) player or on a hard disk drive of a digital computer. 
   For example, portable devices for playing MP3 compressed digital audio recordings that use electronic solid-state memory, e.g., flash-memory, are capable of storing about ten (10) music selections. With an add-in memory card, such devices can carry a total of about twenty (20) music selections. These MP3 players that store the MP3 compressed digital audio recordings in an electronic solid-state memory consume comparatively little electrical power. Thus, such MP3 players provide an extended playing interval without having to power the computer&#39;s CD-ROM or hard disk drive. 
   U.S. Pat. No. 6,226,237, entitled “Low Power CD-ROM Player for Portable Computers”, issued May 1, 2001 (the “&#39;237” patent), which is hereby incorporated by reference in its entirety, describes how a conventional notebook computer, when simply playing a conventional music CD, consumes an unnecessarily large amount of electrical energy. That is largely due to the large number of background functions that are unrelated to the playing of music that the Operating System (e.g., Windows®) is performing whenever the computer is turned on. That excessive electrical energy consumption for functions unrelated to the function the user is performing at the moment, i.e., playing music, quickly drains the battery of a notebook computer of power that could more prudently be applied at another time in performance of microprocessor intensive tasks such as word processing and spreadsheet analysis. The solution presented in the &#39;237 patent is a state machine that operates when main power to the portable device is OFF. The invention of the &#39;237 patent couples a CD-ROM to the audio subsystem (when main power is OFF) so that CDs can be played, without excessive battery drain, or without having to boot up the portable computer. 
   The prior art also includes silicon solutions that are dedicated function integrated circuits (ICs) or incorporated into application-specific integrated circuits, or ASICs. These are usually expensive solutions as the digital signal processor (DSP) required in a dedicated chip results in a large, costly integrated circuit. One of the results is the use of a larger amount of PCB (printed circuit board) space. 
   Further, the 15 to 20 MIPS (million instructions per second) decode engine known in the art must be continuously running to generate the audio stream for the Codec. Additionally, the dedicated decode engine needs to have the high-power-consuming hard disk drive (HDD) continuously operating. These approaches are limited to functioning only with MP3 compression, thereby eliminating the opportunity to adapt the system to newly emerging music compression algorithms, such as Microsoft&#39;s WMA or the music industry&#39;s proposed Secure Digital Music Initiative (SDMI) for secure audio. 
   Dedicated silicon solutions known in the art employ a DSP that must constantly be decoding the compressed audio files from a hard disk drive, which must therefore be constantly reading the audio files. Such known methods require much power, resulting in a fast battery discharge, (e.g., much faster than the possible 4 to 10 hours of desired use on a transoceanic flight). 
   Thus, known hardware MP3 decoder and players requiring an IC implementation and a hard disk drive being accessed non-stop are high in power consumption, difficult to upgrade, and expensive. 
   The present invention provides a solution that is low in power consumption, can be upgraded in the field for various music compression formats, is expected to cost no more than half the cost of the currently available hardware implementation, and may be made capable of playing up to hundreds of musical selections, while only having to access the HDD or CD-ROM less than 0.5% of the time. 
   SUMMARY OF THE INVENTION 
   It is becoming more and more desirable for mobile platform companies to add MP3 and other compressed audio player capability to their products, with low cost, while providing very long music playing time, and perhaps even a player that can be later upgraded to other compression formats by the owner. These mobile platform companies may also want to market differentiate their products within a very short development time frame. 
   The music playing solution of the present invention utilizes a special purpose circuit in combination with the mini-OS (operating system) software of the present invention. The present invention uses the embedded computing power of the standard CPU to perform the file decompression. Since today&#39;s CPUs with clock rates of 500 MHz to 1 GHz have at least an order of magnitude higher processing power than the real time DSP engines used in currently available MP3 player/decoders, these powerful CPU processors can often finish the decoding process in less than 10% of the available time. The CPU may then be set to idle by the present invention for more than 90% of the time, saving large amounts of power and thus greatly slowing the discharge of the battery and extending the useful time of the equipment under battery power on a single charge. 
   The present invention is unlike the real-time DSP engines known in the art, which require a constant data stream from the HDD, and which result in high power consumption, since the HDD is being accessed all the time. Using the technology of the present invention, the HDD may be accessed less than 0.5% of the time with a typical complement of memory, i.e., 128 MB RAM. This results in a dramatic reduction in the rate at which power is dissipated from the equipment battery. Further, minimal PCB changes are required for the present invention, thus resulting in the quick adoption of new product features in PCs. 
   There are many possible music compression algorithms. Compression algorithms other than MP3 include WMA, AAC, and the proposed SDMI. The software decompression methodology of the present invention can be easily modified to decode any compression scheme, or with a software installation process, all the various compression schemes. This flexibility allows the adaptation to new and different algorithms, as they become popular, by permitting an after-market upgrade of computers equipped with the present invention. Also, since this portion of the present invention is a software system, new updates and/or algorithms may be downloaded (e.g., from the Internet) to upgrade machines in the field, eliminating the necessity for consumers to buy multiple players/decoders in order to listen to audio files having different compression formats. 
   Thus, the present invention provides a low-cost, low power-consumption, long-battery-life audio playing and decoding system, which may be used to play audio files of various formats. 
   In one aspect, a computer system adapted to play audio files comprises a system CPU, memory; at least one drive comprising compressed audio data residing in one or more audio files, a play list software program for selecting and storing a play list comprising one or more of the audio files, a first operating system adapted to control at least the system CPU and memory, and a second operating system stored in BIOS and adapted to retrieve the play list and cause the drive to read at least one audio file of the play list, to cause the system CPU to decompress the compressed audio data of the file and provide decompressed audio data, and to cause the decompressed audio data to be stored in memory. 
   In another aspect, a computer system adapted to play audio files comprises a drive comprising at least one audio file, an audio controller, and an operating system stored in BIOS, the operating system controlling the audio controller, so as to cause the audio controller to play at least one audio file. 
   In a further aspect, a computer system adapted to play audio files comprises: compressed audio data, a system CPU, an audio controller, a first operating system adapted to control at least the system CPU, a second operating system controlling the audio controller and system CPU, so as to cause the system CPU to decompress the compressed audio data, and a switch, the activation of the switch causing the second operating system to boot. 
   In yet another aspect, a computer system adapted to play audio files comprises a system CPU, memory, at least one drive comprising compressed audio data residing in one or more audio files, a play list software program for selecting a play list comprising one or more of the audio files, and an audio controller coupled to the system CPU, memory and drive. The audio controller is adapted to cause the drive to read at least one audio file of the play list, to cause the system CPU to decompress the compressed audio data of the file and thereby provide decompressed audio data, and to cause the decompressed audio data to be stored in memory. 
   In process form, a method of playing audio files on a computer system comprises: booting a first operating system; creating and storing a play list comprising a list of compressed audio files residing on one or more drives of a computer system having at least a drive, a CPU, and a memory; terminating the first operating system; booting a second operating system upon activation by a switch; reading the play list; reading the compressed audio files from the drive based on the play list; providing the compressed audio data to the CPU for decompressing the data of the compressed audio file into decompressed audio data; storing the decompressed audio data in memory; and retrieving the decompressed audio data from the memory for playing. 
   In another process form, a method of playing audio files on a computer system comprises: reading compressed audio data from the drive of a computer system having at least a drive, a CPU, and a memory; providing the compressed audio data to the CPU for decompressing the compressed audio data, thereby providing decompressed audio data; and storing the decompressed audio data in memory. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram representation an exemplary operational flow of one embodiment of the present invention; 
       FIG. 2  is a flow diagram of an exemplary power up of the mini-OS and initiation of the player function, in one embodiment of the present invention; 
       FIG. 3  is a block diagram of an exemplary audio player system consistent with one embodiment of the present invention; and 
       FIG. 4  is a block diagram of the internal portion of an exemplary special purpose circuit, in relation to the other components that interface with it, in one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The present invention comprises mini-OS (operating system) software and a hardware interface between the South Bridge and Codec to play the musical selections (or other stored audio) desired by the user. The mini-OS software of the present invention performs only those functions and enables those elements of the portable computer that are needed, when they are needed, to play the selected music, without performing all of the background functions performed by the full system operating system, e.g., Windows®, and without accessing the monitor circuitry and monitor screen of the portable computer. Additionally, the mini-OS of the present invention only accesses the HDD when compressed files are being transferred to RAM. Thus, it will be seen that the mini-OS software portion of the present invention performs both power saving and file management functions when playing audio. 
     FIG. 1  is a block diagram representation of the operational flow of the exemplary software compressed audio player in one embodiment of the present invention. 
   The operational concept illustrated in  FIG. 1  is as follows:
         1 st : A browser, running on a full system operating system, e.g., Windows®, of the portable computer is initially used to download compressed music files (for example 1000 songs) onto the PC hard disk drive (HDD) ( 2 ) (e.g., using 4 gigabytes of HDD space) at some time prior to the time at which the user desires to use the portable computer as an audio player and a playlist is created, comprising the songs the user desires to hear at a later time;   2 nd : When the user desires to use the portable computer as an audio player, once the desired music files are on the HDD, the user operates an audio player on-switch to turn the portable computer fully on, boot up the entire computer, load in the mini-OS of the present invention instead of the usual Microsoft Windows® OS (the full system operating system is not opened) with the power saving initialization subroutines and initializes only those portions of the portable computer as necessary, and the file management subroutines initialize the song play list or book generated in step 1, of a substantial number of songs, for desired music listening under direction of the user;   3 rd : The mini-OS software is then copied from the HDD ( 2 ) to RAM ( 4 ), and then the first set of compressed files from the song play list is copied from the HDD ( 2 ) to the system RAM ( 4 ) also using the mini-OS software of the present invention. For example, in today&#39;s PC&#39;s 128 Mbytes is a typical system RAM size, with the mini-OS software of the present invention taking about 8 Mbytes of the RAM, leaving approximately 120 Mbytes for use as a compressed music memory (i.e., a cache or buffer, using system memory, dedicated memory, or other memory). That 120 Mbytes represents about 2 hours of continuous compressed music with a compression ration of 10:1, typical of MP3 files. Similarly, in the case when flash media is used for MP3 storage, all or most of the contents of the flash media card can be copied to the system RAM ( 4 ), thus minimizing the access of the flash media reader and allowing for a more responsive control over the MP3 files;   4 th : The file management software of the present invention sequentially delivers portions of the first music file to the CPU ( 6 ) where the decode algorithm decompresses each file using the file management software of the present invention stored in RAM ( 4 ). Once decoded, the PCM audio data is transferred in one of three ways: the CPU delivers the PCM audio data to the South Bridge (see  FIG. 3  ( 32 )) FIFO buffer; the DMA in the South Bridge transfers the data internally within the South Bridge to the FIFO buffer; or the special purpose circuit transfers the data to the FIFO buffer from the LPC interface. The FIFO buffer then sequentially feeds each piece of decoded music to Codec ( 8 ) (also see  FIG. 3  ( 42 )), through the special purpose circuit of the present invention, where the decoded signal is converted from digital to analog.       

   Then the output signal from the Codec ( 8 ) is amplified ( 10 ) (also see  FIG. 3  ( 44 )) to drive the speakers and/or headset (see  FIG. 3  ( 46 )).
         5 th : While the final song of the first set from the play list is playing from memory, the file management software of the present invention stored in the RAM ( 4 ,  30 ) returns control to the 4 th  step to retrieve the next set of compressed music files from the memory of the RAM, as determined by the earlier scripted song play list developed in the 1 st  step. Thus, the 4 th  and 5 th  steps are repeated for each set of compressed music files until the last music selection in the set plays. At that point in time control returns to the 3 rd  step to load another set from the play list, which is similarly played through the 4 th  and 5 th  steps. When the last song is played from the overall play list of the 2 nd  step, or when the user turns off the music player function, the operation of the player ceases.       

   The mini-OS power saving software of the present invention ensures that the CPU, Peripheral Chips, HDD and other controllable system elements will be in idle state for the highest percentage time possible. An interesting attribute of the solution offered by the present invention is that the higher the MIPS (Million Instructions Per Second) capacity of the CPU, the smaller percentage of time the CPU will spend performing the decode function. This means that higher performance CPU&#39;s will demonstrate even lower power usage when playing compressed music performances, thus saving even more battery power and further extending the length of time that the battery maintains sufficient charge to power the portable computer. 
   The mini-OS monitors the audio control buttons (e.g., play, fast forward, rewind, pause, scan, previous track, next track, first track, last track, fast forward/rewind while listening, audio source/media select (e.g., HDD or CD), etc.) (see  FIG. 3  ( 48 )) for user actuation through the special purpose circuit (see  FIG. 3  ( 40 )) of the present invention, and communicates user requests to the mini-OS file management software of the present invention. Optionally, a small LCD display (see  FIG. 3  ( 34 )) can be connected to the special purpose circuit to provide visual status indicators (e.g., Song #, Song titles, track #, Playtime &amp; icons) under control of the mini-OS display management subroutines. 
   The mini-OS power saving software of the present invention primarily manages the usage of the CPU, and the MP3 storage devices such as CD, HDD, and flash media such as SD (Secure Digital) cards, MMC (Multimedia Card), memory stick, and SMC (Smart Media Card), while maintaining the rest of the system, including the memory, corelogic chipsets, in a fully on and functional state. Secondary power saving is applied to other PC subsystems to minimize power usage still further by putting them in an idle state. 
   For example, with a 500 MHz Pentium III CPU having about 225 MIPS of processing power and the decode algorithm requiring about 15 MIPS, the CPU will be operating less than 10% of the time. The other 90-95% of the time the CPU will be in a standby mode that requires only milliamps of current. Alternatively, the CPU can be run at a slower clock speed, which is usually an option provided by most of today CPUs, such as the AMD&#39;s Athlon CPU. Similarly the HDD is accessed during the time it takes to fill or refill the RAM. Thus, since the average song takes about 4 minutes to play and the RAM holds about 30 songs for 120 Mbytes, and since the HDD needs 1-5 seconds to spin up and only several seconds to load the song play list into RAM, the total access time for the HDD may be 30 seconds out of 120 minutes of play time; a ratio of 1:240, less than 0.5% of full power operating time. These factors add to the power savings gained by using the mini-OS of the present invention instead of the full operating system of the portable computer. The result of the overall power consumption of the present invention is very low when the portable computer is in the music play mode, and that directly translates into the battery maintaining a useful charge level for a much longer time than allowed by the prior art. As those skilled in the art will recognize, the compressed music data of this invention may reside on a hard disk, on other magnetic (e.g., tape) media, optical (e.g., CD-ROM) media, flash media (e.g., SD cards, MMC, memory stick, SMC), or any other storage medium. 
     FIG. 3  is a generalized overall block diagram of an exemplary system  31  consistent with one embodiment of the present invention. The majority of the blocks in system  31  are components known in the art and are generally included in all PC computers for producing sound through the speaker of the computer. Shown here is a system clock  56 , which, for simplicity of  FIG. 3 , is not shown connected to the various components that need a clock signal. Additionally, CPU  26  is shown interfacing with North Bridge  28 . In turn, North Bridge  28  interfaces with system RAM  30  and South Bridge  32 . Then South Bridge  32  interfaces with HDD  36  and CD-ROM  38 . Typically South Bridge  32  also interfaces directly with Codec  42  through AC_link; however, in the exemplary system  31  shown, special purpose circuit  40  (see discussion of  FIG. 4  below) is inserted between South Bridge  32  and Codec  42  to enable the playing of compressed digital audio in conjunction with the mini-OS  80  of the present invention from system RAM  30 , without affecting the ability to play non-compressed analog audio. In this configuration, the mini-OS  80  is stored in the BIOS, although those skilled in the art will recognize that the mini-OS could alternatively be stored in its own ROM (either within special purpose circuit  40  or external to it), a hard disk, or other media. Thus, AC_link 1  from South Bridge  32  is coupled to special purpose circuit  40 , which performs the decompression function as necessary, and then provides any audio signals to Codec  42  via AC_link 2 . Codec  42  then performs the usual function on all signals received from special purpose circuit  40  and applies the audio signals to amplifier  44 , to be played on speaker  46  or headphones (not shown). In system  31 , AC_link 1  looks and behaves like the standard AC_link to South Bridge  32 , and AC_link 2  looks and behaves like the standard AC_link to Codec  42 , making it appear to those portions of the computer that audio functions are being performed as during normal (i.e., known in the art) audio play, thus having minimal or no impact on the operation of South Bridge  32  and Codec  42 . Also shown in  FIG. 3  are function switches  48 , small LCD display  34  and audio player power switch  54 , which function as described hereinbelow with reference to  FIG. 4 . 
     FIG. 4  includes a detailed block diagram of the internals of special purpose circuit  40  and related details of the other portions of the computer that the special purpose circuit interfaces without showing all of the details of the rest of the computer system. Special purpose circuit  40  may be produced as an IC to minimize the PCB space needed to incorporate embodiments of the present invention into portable computers. South Bridge  32  is shown with the standard AC  97  controller  50  and LPC (low pin count) controller  52  to the left of special purpose circuit  40  with the standard bidirectional links AC_link 1  and LPC Bus between them, and the unidirectional IRQ (Interrupt Request) link from special purpose circuit  40  to South Bridge  32 . To the right, special purpose circuit  40  provides uncompressed audio to AC  97  Codec  42  via AC_link 2 . Also, to the right, function keys  48 , and below LCD  34 , are each shown connected to special purpose circuit  40 . Additionally,  FIG. 4  includes system clock  56  connected to various components, and in the lower left, audio player power switch  54 . Power switch  54  is provided so that when the user initiates the player mode via power switch  54 , only the mini-OS (instead of the full system OS) is initiated, for use in a system consistent with the present invention. 
   Internal to special purpose circuit  40  are switches  60  that interface with both AC_link 1  and AC_link 2  and function in response to settings in an internal register of register block  66 , with switches  60  closed connecting AC-link 1  with AC_link 2  when the PC functions normally with the full system OS, and with switches  60  open when a system consistent with the present invention is employed. The LPC path is coupled to LPC interface. Switches  60  and AC_link 2  are coupled to state machine  64 , while another port of state machine  64  is coupled, via bus  74 , to the output of LPC interface  62 , as well as register block  66 , function key interface  68  and LCD interface  72 . A second port of register block  66  is also coupled to a third port of state machine  64 . Function keys  48  are coupled to function key interface  68 , and LCD  34  is coupled to LCD interface  72 . Also, function key interface  68  provides a signal to register block  66  when one of the function keys  48  is selected by the user. Audio player power switch  54 , which is operated by the user in the second step discussed above, may be used to activate the PC to operate as described hereinabove. Switch  54  is shown connected to the DC voltage source of the portable computer and not to any particular block in  FIG. 4 , since that connection varies depending on several factors controlled by the manufacturer of the computer on which an embodiment of the present invention is installed. 
   More specifically, the blocks within special purpose circuit  40  operate as follows: 
   LPC Interface 
   Special purpose circuit  40  includes LPC (Low Pin Count) interface  62  to interface with LPC controller  52  in South Bridge  32 . 
   The LPC interface  62  is used to by CPU  26  to:
         (1) read the function key input registers in register block  66 ;   (2) set the control register in register block  66  to control the AC 97  Codec  42 ;   (3) get the audio PCM (Pulse Code Modulation) data from the system memory (RAM  30 ); and   (4) perform clock throttling control.       

   The setting in the mode register of register block  66  controls the state of switches  60  to switch the special purpose circuit  40  between the normal computer operation mode with switches  60  closed (e.g., running Microsoft Windows® OS) and the mode of a system consistent with the present invention, with switches  60  open (running the mini-OS) to play compressed audio files. 
   South Bridge AC 97  Controller  50  Interface (AC_Link 1  from Host) 
   During the normal computer operation mode, switches  60  are closed with the South Bridge AC 97  Controller  50  interface connected directly through, closed switches  60 , to AC 97  Codec  42  to generate audio output as if special purpose circuit  40  were not present. To play compressed audio files, switches  60  are open when the mini-OS is running, and state machine  64  controls AC 97  Codec  42 . 
   AC 97  Codec Interface (AC_Link 2  to AC 97  Codec  42 ) 
   When the computer is running under control of the mini-OS, switches  60  are open. State machine  64  then controls the AC_link 2  in response to the settings of the register block  66  set by the host (CPU  26 ) to generate the controls for AC 97  Codec  42  (e.g., switching the sampling frequency, controlling volume, sending the PCM data to the Codec  42 , setting the Codec  42  to the power saving mode or waking Codec  42  from the power saving mode). 
   Function Key Input Interface  68   
   Function key interface  68  receives the user selections from function keys  48  and stores the selections in internal registers to be read by CPU  26 . 
   LCD Interface  72   
   LCD interface  72  is only necessary if LCD  34  is used to provide status information to the user. The purpose, when used, is to show player status on low cost LCD  34  when the system consistent with the present invention is used. Status of the audio track number of the selection playing, status icons (e.g., Play) and other generic status icons may be programmed into the system and displayed for any other purpose. 
   Operation Modes 
   (A) Normal Operation Mode: 
   When the PC is fully powered and running under the full system OS, the various functions of special purpose circuit  40  are bypassed and switches  60  are closed, as discussed above. In the normal mode, the computer system uses the South Bridge AC 97  Controller  50  to directly control the AC 97  Codec  42  through the AC_link (in the Normal mode AC_link 1  and AC_link 2  are the same since switches  60  are closed). The special purpose circuit does not intercept or modify the AC_link signals. 
   (B) Compressed Audio Performance Mode: 
   When switch  54  has been closed, the system runs under the control of mini-OS, and special purpose circuit  40  is empowered and runs in the compressed audio performance mode. The South Bridge AC 97  Controller  50  is isolated from the AC 97  Codec  42  in this mode since switches  60  are open. 
   In the compressed audio performance mode, the host (CPU  26 ) sets the internal registers of register block  66  to control the data flow to the AC 97  Codec  42 , and to perform the various power management functions. 
   A Power Saving Control Method in Compressed Audio Performance Mode 
   A flexible control method of the special purpose circuit  40  is provided to minimize the system control cycles and power consumption in the performance mode. The system memory (RAM  30 ) is used to pass most of the control commands to the special purpose circuit  40 , instead of CPU  26 , which minimizes the time that CPU  26  needs to access high speed external bus other than a standby level. This considerably reduces the power load on the portable computer battery in this mode. 
   CPU  26  also sets the system control memory registers in register block  66 . State machine  64  bases operation on those register settings to obtain control words and PCM data automatically through the LPC interface  62 . The control words in the system memory (RAM  30 ) are fetched into the internal registers, and the state machine  64  decodes the control words to determine if PCM or audio data is ready. If the audio data is ready, the state machine  64  continues to fetch the audio data and send it to the AC 97  Codec  42 . The control words in the system memory (RAM  30 ) can also be used to indicate the sampling frequency of the PCM data. So, the state machine  64  can set AC 97  Codec  42  to the appropriate frequency before the PCM data is sent. 
   Those skilled in the art will recognize that a headphone or headset system may comprise further functionality than described hereinabove, e.g., a volume control, or the audio control buttons may be integrated thereto. 
   It should also be recognized that a special purpose circuit consistent with the invention may be integrated into a full-time compressed (and/or non-compressed) audio playing system capable of playing music regardless of the operation of the rest of the system. In this configuration, the special purpose circuit and mini-OS are provided, as well as a software driver for handling interrupts from the function buttons under Windows®. In this configuration, when the rest of the system is either fully on (S 0 ) or in “sleep” (suspend to RAM or S 3 ) mode, the system may be configured to begin execution of a custom or standard audio player, e.g., Music Match or Windows® Media Player, running under Windows®, which may be adapted to play the compressed audio files stored in the play list. In this scenario, the function buttons may be adapted for use in a passthrough-type mode using the accompanying software driver to control various features of the audio player software, e.g., Music Match, instead of controlling the special purpose circuit. When the primary operating system such as Windows® is either fully off (S 5 ) or in “hibernate” (suspend to HDD or S 4 ) mode, operation of the special purpose circuit may proceed to play compressed audio files from the play list as described hereinabove, wherein the function buttons control the special purpose circuit. 
   It is noted that the power states described above (i.e., fully on, sleep/suspend to RAM, fully off, hibernate/suspend to HDD) are often referred to using the Advanced Configuration and Power Interface (“ACPI”) standard conventions, as follows: The typical operating system (e.g., Windows®) supports six system power states, referred to as S 0  (fully on and operational) through S 5  (power off). Each state is characterized by the following: power consumption, i.e. how much power the computer uses; software resumption, i.e, from what point the operating system restarts; hardware latency, i.e., how long it takes to return the computer to the working state; and system context, i.e. how much system context is retained, or whether the operating system must reboot to return to the working state. State S 0  is the working state. States S 1 , S 2 , S 3 , and S 4  are sleeping states, in which the computer appears off because of reduced power consumption but retains enough context to return to the working state without restarting the operating system. State S 5  is the shutdown or off state. A system is waking when it is in transition from the shutdown state (S 5 ) or any sleeping state (S 1 -S 4 ) to the working state (S 0 ), and it is going to sleep when it is in transition from the working state to any sleep state or the shutdown state. the system cannot enter one sleep state directly from another; it must always enter the working state before entering any sleep state. For example, a system cannot transition from state S 2  to S 4 , nor from state S 4  to S 2 . It must first return to S 0 , from which it can enter the next sleep state. Because a system in an intermediate sleep state has already lost some operating context, it must return to the working state to restore that context before it can make an additional state transition. 
   Referring now to  FIG. 2 , in conjunction with  FIG. 3 , an exemplary sequence  200  for the power up of the mini-OS and initiation of the player function, in one embodiment of the present invention, is illustrated. As stated above, at some time prior to the initiation of the audio player function of a PC equipped with the present invention, the user downloads (not shown in  FIG. 2 ) the audio files of interest to the HDD  36  or burns a CD-ROM that is placed in the CD-ROM drive  38  for use with the audio player feature of the present invention. As shown, at step  201 , the sequence  200  begins when the user presses either an audio player power switch  54  or the computer&#39;s main power switch (not shown in  FIG. 3 ), to turn the system on. A determination is then made, at step  202 , whether the computer is to boot in normal operation mode or compressed audio performance mode. This determination is typically made in the BIOS, based on whether the computer&#39;s power switch or an audio player power switch  54  was used to turn on the computer, although those skilled in the art will recognize that this determination could alternatively be made by an application program or an operating system that provides such capability (e.g., Windows®98). If the computer&#39;s power switch was used to turn on the computer, then the system boots to normal operation mode, at step  203 , and the normal operating system (e.g., Windows®98) is loaded into system RAM  30  and executed. If an audio player power switch  54  was used to turn on the computer, the mini-OS is loaded into system RAM  30 , at step  204 . At step  205 , the mini-OS initializes the system components including one or more of the North Bridge  28 , South Bridge  32 , special purpose circuit  40 , hard drive  36 , CD-ROM drive  38 , codec  42 , and CPU  26 . 
   Since no audio decompression request will be pending upon system initialization (i.e., the memory buffer is not full), which determination is made at step  208 , the system waits for input from one of the function keys  48 , at step  207 , until one of the function keys  48  is pressed, at which point the appropriate function is executed and the LCD display updated, as appropriate, at step  206 . If the command includes a request from the user to play audio, an audio decompression request will be pending at this time, which determination is made at step  208 . Since no compressed audio file(s) are in system memory  30  upon the initial request to play audio, which determination is made at step  209 , the compressed audio file(s) are read from the HDD  36  and/or CD-ROM drive  38  and loaded into system memory  30 , at step  210 . After the compressed audio files are loaded into system memory at step  210 , or if the audio file(s) are already in system memory, which determination is made at step  209 , the audio files are then decompressed, at step  211 , using the system CPU  26 . DMA transfer(s) to the codec  42  are initialized for the decompressed audio data, at step  212 , and then the output signal from the Codec  42  is amplified (not shown in  FIG. 2 ) by the amplifier  44  to drive the speakers and/or headset  46 . After the DMA transfer(s) are initialized, at step  212 , control loops back to step  208 , to determine whether an audio decompression request is pending. 
   It should be recognized by those skilled in the art that, although the above-described embodiments utilize a hardware-based OS selection (i.e., pressing main power button boots to Windows®, while pressing audio control button boots to mini-OS), other OS selection methods are contemplated, as well. Such selection methods include, e.g., using a batch file or other scripting or software-based method to shut down a first OS and boot to the second OS. Those skilled in the art will also recognize that the mini-OS of the present invention could conceivably be implemented as part of a larger OS (e.g., a GUI-based OS, such as Windows®, LINUX, etc.) or as a software component named something other than an “operating system”, (e.g., a “driver”, an “algorithm”, a “script”, “code”, a “program”, an “executable”, a “routine”, a “subroutine”, a “utility”, etc.), instead of being implemented as an entirely separate operating system. Such embodiments are contemplated to be within the scope of the present invention. 
   Although the present invention has been described in terms of the exemplary embodiments provided herein, it is to be understood that such disclosure is purely illustrative and is not to be interpreted as limiting. Consequently, without departing from the spirit and scope of the invention, various alterations, modifications, and/or alternative applications of the invention will, no doubt, be suggested to those skilled in the art after having read the preceding disclosure. Accordingly, it is intended that the following claims be interpreted as encompassing all alterations, modifications, or alternative applications as fall within the true spirit and scope of the invention.