Abstract:
In an digital video disk player the timely acquisition of specific data types is particularly important during trick mode operation. During trick modes a controller can provide enhanced control capability by employing interrupt requests having priorities that differ from those used during normal play mode operation. A method for controlling a microcontroller in digital disk apparatus having at least two reproducing modes. The method comprises the steps of prioritizing the microcontroller interrupts during a first reproducing mode, and in a second reproducing mode reordering the microcontroller interrupt priorities.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit of an earlier filing date under 35 U.S.C, 120, from co-pending application Ser. No. 09/024,323 filed Feb. 17, 1998 which claims benefit from provisional application serial No. 60/039,573 filed Feb. 18, 1997. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to the reproduction of a digitally encoded signal from a disk medium and in particular to optimizing reproduction at other than play speed.  
         BACKGROUND OF THE INVENTION  
         [0003]    The introduction of disks recorded with digitally compressed audio and video signals, for example, utilizing MPEG compression protocols, offers the consumer sound and picture quality virtually indistinguishable from the original material. However, consumer users will expect such digital video disks, DVDs or hard disk drives to offer features similar to those of their analog video cassette recorder or VCR. For example, a VCR may reproduce in either forward or reverse directions at speeds other than the recorded speed. Such non-standard speed playback features are also known as trick play modes. The provision of trick play features are less easily provided with MPEG encoded video signals due to the hierarchical nature of the compression which forms pictures into groups having varying degrees of compression. These groups are termed groups of pictures or GOPs, and require decoding in sequence. A detailed description of the MPEG 2 standard is published as ISO/IEC Standard 13818-2. However, in simple terms, an MPEG 2 signal stream may comprise three types of pictures having varying degrees of content compression. An intra-coded frame or I frame has the least compression of the three types and may be decoded without reference to any other frame. A predicted frame or P frame is compressed with reference to a preceding I or P frame and achieves greater degree of compression than an intra-coded frame. The third type of MPEG frame, termed a bi-directionally coded or B frame, may be compressed based on predictions from preceding and/or succeeding frames. Bi-directionally coded frames have the greatest degree of compression. The three types of MPEG frames are arranged in groups of pictures or GOPs. The GOP may for example contain 12 frames arranged as illustrated in FIG. 1A. Since only an intra-coded frame is decodable without reference to any other frame, each GOP may only be decoded following the decoding of the I frame. The first predicted frame or P frame, may be decoded and stored based on modification of the stored, preceding I frame. Subsequent P frames may be predicted from the stored preceding P frame. The prediction of P frames is indicated in FIG. 1A by the curved, solid arrow head lines. Finally, bi-directionally coded or B frames may be decoded by means of predictions from preceding and or succeeding frames, for example, stored I and P frames. Decoding of B frames by predictions from adjacent stored frames is depicted in FIG. 1A by the curved, dotted arrow head lines.  
           [0004]    The hierarchical nature of the coded frames comprising MPEG groups of pictures necessitates that the I and P frames of each GOP are decoded in the forward direction. Thus, reverse mode features may be provided by effectively jumping back to an earlier, or preceding I frame and then decoding in a forward direction through that GOP. The decoded frames being stored in frame buffer memories for subsequent read out in reverse to achieve the desired reverse program sequence. FIG. 1B illustrates play back in the forward direction at normal speed and at a time prior to time t 0 , a reverse three times speed mode trick play mode is selected. The trick play mode is initiated at time t 0  where I-frame I( 25 ) is decoded and displayed. The next frame required for decoding is I-frame I( 13 ), thus the transducer is repositioned, as indicated by arrow J 1  to acquire frame I( 13 ). Having recovered and decoded I-frame I( 13 ), the transducer tracks, as indicated by arrow J 2  to acquire and decode frame P( 16 ). The process is repeated as indicated by arrows J 3 , J 4 . Following the acquisition and decoding of frame P ( 22 ) the transducer is moved as depicted by arrow Jn to recover frame I( 1 ). To smoothly portray scene motion requires the decoding and display of I, P, and possibly B-frames. The jump and play process is repeated for preceding GOP, thereby progressing haltingly backwards through the records whilst smoothly portraying the program material in a reverse sequence at the video output.  
         SUMMARY OF THE INVENTION  
         [0005]    In an digital video disk player the timely acquisition of specific data types is particularly important during trick mode operation. During trick modes a controller can be optimized to provide enhanced performance capability by employing interrupt requests having priorities that differ from those assigned for normal play mode operation. A method for controlling a microcontroller in digital disk apparatus having at least two reproducing modes comprises the steps of prioritizing the microcontroller interrupts during a first reproducing mode, and in a second reproducing mode reordering the microcontroller interrupt priorities. In a third reproducing mode the reordered interrupt priorities are changed, and certain ones of the changed reordered interrupt priorities are deleted. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1A illustrates an MPEG 2 group of pictures.  
         [0007]    [0007]FIG. 1B illustrates recorded groups of pictures, during replay and reverse trick play at three times speed.  
         [0008]    [0008]FIG. 2 is a block diagram of an exemplary digital video disk player including inventive arrangements.  
         [0009]    [0009]FIG. 3 is a block diagram showing in greater detail part of FIG. 2 depicting various inventive arrangements.  
         [0010]    [0010]FIG. 4 is a block diagram depicting in detail inventive arrangements of FIG. 2.  
         [0011]    [0011]FIG. 5 depicts an exemplary control sequence in accordance with an inventive arrangement of FIG. 4. 
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIG. 2 depicts an exemplary block diagram of a digital video disk player. In block  10  a deck is shown which may accept a digitally recorded disk  14  for rotation by a motor  12 . A digital signal is recorded on disk  14  as a spiral track containing pits with respective pit lengths determined by an 8/16 modulation coding responsive to respective signal data bits. The record on disk  14  is read by pick up  15  which gathers reflected illumination from a laser. The reflected laser light is collected by a photo detector or opto pick-up device. An imaging device, for example a lens or mirror, which form part of transducer pick-up  15 , is servo controlled and driven by motor  11  to follow the recorded track. Different parts of the recording may be accessed by rapidly repositioning the imaging device. Servo controlled motors  11  and  12  are driven by integrated circuit drive amplifier  20 . Pick up  15  is coupled to an opto preamplifier, block  30 , which includes drive circuitry for the laser illuminator and a preamplifier which provides amplification and equalization for the reflected signal output from the opto pick-up device. The amplified and equalized replay signal from opto preamplifier  30  is connected to a channel processor block  40  where the replay signal is employed to synchronize a phase locked loop which is utilized to demodulate the 8:16 modulation employed for recording.  
         [0013]    The MPEG encoded bitstream is encoded for error detection and correction by means of Reed Solomon product coding which is applied in blocks of 16 sectors, where each sector contains 2048 bytes of payload data. Thus following 8:16 demodulation the replay data stream is de-interleaved or unshuffled and error corrected by means of Reed Solomon product correction implemented in ECC buffer memories  45  and  46  of FIG. 4. Each buffer stores 16 sectors of the replay data stream arranged as an array to facilitate de-interleaving and to enable the required row and column product processing. The cascaded ECC buffer memories introduce a delay to reproduced serial bit stream of approximately (2*16*1.4) milliseconds, where 2 represents the pair of ECC buffers, 16 represents the sectors over which the correction is applied and 1.4 milliseconds represents a sector period at 1X rotational speed. Thus the reproduced serial bit stream is delayed by a minimum of approximately 45 milliseconds.  
         [0014]    The error corrected signal bitstream  41  is coupled via a link processor to a bit stream or mechanical/track buffer memory  60 A. The track buffer comprises a DRAM memory type and is used to store an amount of replayed data such that data losses during transducer or pickup  15  repositioning will not result in any visible deficiency when decoded. Thus the final output image stream will appear to be continuous or seamless to the viewer. Bitstream buffer memory  60 A is part of an exemplary 16 megabit DRAM memory. A further exemplary 16 megabit SDRAM memory block is partitioned to provide frame buffers  60 C and  60 D which provide storage for at least two decoded image frames of compressed video bit stream storage prior to decoding and storage in buffer  60 B, an audio bit stream buffer  60 E and other storage in buffers  60 F, G and H. The channel processor  40  also includes timing control circuitry which control writing by link  505  to bitstream buffer  60 A. Data may be intermittently written to the bitstream buffer as a consequence of changes in replay track addresses, for example, resulting from user defined replay video content choices such as “Directors cut”, parental guidance, or even user selectable alternative shot angles. To facilitate more rapid access and recovery of the recorded signal, disk  14  may be rotated at an increased speed resulting in the transduced bitstream having a higher bit rate, and possibly intermittent delivery.  
         [0015]    The digital video disk player is controlled by a central processing unit or CPU element  510 , for example ST Microelectronics type ST 20 , of block  500 , which accepts the reproduced bitstream and error flags from channel IC  40 , and provides control instructions to servo IC  50 . In addition, CPU  510  accepts user control commands from user interface  90 , and MPEG decoder control functions from the MPEG decoder element  530  of block  500 . A system buffer memory  80  is addressed by and provides data to CPU  510 . For example, buffer  80  may comprise both RAM and PROM memory locations. The RAM may be used to store various data extracted from bitstream  41  by CPU  510 , for example such data may include descrambling or decryption information, bitstream and frame buffer memory management data, and navigation data. The PROM may, for example contain advantageous transducer jump algorithms which facilitate trick mode operation at a selection of speeds in forward or reverse directions.  
         [0016]    The MPEG encoded bitstream is coupled to link processor  505  in FIG. 3, which may function as a hardware demultiplexor to separate audio, video and control information from the encoded bitstream. Alternatively, bitstream demultiplexing may be accomplished by software control of direct memory access or DMA of buffer  60 A, from CPU  510  of FIG. 3. The encoded bitstream in track buffer  60 A is searched by microcontroller  510  to locate and read headers and to extract navigation data.  
         [0017]    Having identified sector addresses or headers, microcontroller  510  controls direct memory access of buffer  60 A which effectively separates MPEG data from other DVD formatted data stored in the buffer. Thus, video DMA  515  separates compressed video bits which are coupled for storage in exemplary video bit buffer  60 B. Similarly compressed audio bits are read from buffer  60 A and stored in audio buffer  60 E. Sub-picture data is also retrieved from track buffer  60 A by DMA and stored in buffer  60 F.  
         [0018]    The compressed video bit stream in video bit buffer  60 B is searched to locate picture or higher level start codes by start code detector  520 . A detected start code signal  512  is coupled to microcontroller  510  which then communicates with MPEG decoder  530 , via signal  511 , to indicate the next picture type, the quantizer setting and to initiate decoding. A decoder status signal  513  is coupled back to microcontroller  510  to indicate the completion of decoding and that picture data available for display or storage. Compressed video bit buffer  60 B may be considered to function as a FIFO or circular buffer where the stored bitstream is sequentially accessed for MPEG decoding, however, trick mode operation may be advantageously facilitated by random access of buffer  60 B, as will be described.  
         [0019]    Within MPEG decoder  530  the video bit stream is processed by a variable length decoder  531  which searches the bitstream to locate slice and macro-block start codes. Certain decoded pictures from each group of pictures are written to frame buffers  60 C and  60 D for subsequent use as predictors when deriving or constructing other pictures, for example P and B pictures, of the GOP. Frame buffers  60 C and  60 D have a storage capacity of at least two video frames. Separated audio packets are stored in audio bit buffer  60 E which is read out and coupled for audio decoding in block  110 . Following MPEG or AC3 audio decoding a digitized audio signal results which is coupled to an audio post processor  130  for digital to analog conversion and generation of various base band audio signal outputs. A digital video output signal is reconstructed in display buffer  580  from decoded blocks read from reference frame buffer  60 C/D. However, during trick mode operation the output signal source may be an advantageous field memory thus block to raster scan conversion within display buffer  580  may be advantageously controlled responsive to trick mode operation. The display buffer is coupled to encoder  590  which provides digital to analog signal conversion and generates baseband video components and encoded video signals.  
         [0020]    Operation of the exemplary video player illustrated in FIG. 2 may be considered with reference to FIG. 1B which illustrates a forward play and reverse trick play sequence. As described previously, the coded relationship existing within each GOP necessitates that each group of pictures is decoded in a forward direction starting from an I-frame or picture. Thus, reverse mode features may be provided by effectively jumping back to transduce an earlier, or preceding I picture and then decoding in a forward direction through that GOP. The decoded pictures are stored in frame buffer memories for subsequent read out in reverse order. However, sequences that include B pictures may utilize further advantageous features which will be described. In FIG. 1B it will be assumed that at some time prior to time t 0 , for example at I-picture I( 1 ), the exemplary video player assumed a forward play condition in response to a user command. Each group of pictures is decoded in the forward direction as illustrated in FIG. 1A by the arrow headed lines linking I, B and P frames. At a time prior to time t 0 , a three times play speed reverse trick mode is selected, and initiated at time t 0  where I-picture I( 25 ) is decoded and displayed. As previously described the next picture required for reverse trick play decoding is I-picture I( 13 ), thus the transducer is moved, as indicated by arrow J 1  to acquire picture I( 13 ). The signal recovery and decoding then follows a play sequence indicated in FIG. 1B by arrows J 1 , to acquire I( 13 ), J 2 , to acquire P( 16 ), J 3 , to P( 19 ), J 4  to P( 22 ) . . . Jn. The intervening B pictures shown in FIG. 1B are transduced but may be discarded as required by each specific trick play mode. To avoid the previously described requirement for additional reverse mode video buffering, various advantageous methods for MPEG decoder control and buffer control and allocation are employed.  
         [0021]    The location and determination of start codes prior to picture decoding may be facilitated by an arrangement which utilizes the link interface block  505  of FIG. 3 to search for start codes in the bitstream prior to buffer  60 A. Such use of link interface  505  advantageously provides early pre-processng of picture headers which may be signaled to microprocessor  510 . Thus, having identified picture headers, pictures wanted by a specific trick mode may be stored in exemplary track buffer  60 A with unwanted pictures deleted by overwriting in the buffer.  
         [0022]    The processing of the video packet stream prior to the video bit buffer  60 B may be advantageously employed for trick mode operation. For example, at a trick play speed or in a reverse replay mode, such pre-processing permits trick play specific selection between pictures to be buffered for decoding, and those unwanted pictures to be discarded before decoding. Such picture selection, for example discarding B-frames, may approximately double the number of I and P pictures stored in video bit buffer  60 B during trick play operation. Thus by selection and deletion, video bit buffer  60 B stores only wanted, or trick play specific pictures, hence more video object units or VOBUs may be stored facilitating enhanced trick play operation.  
         [0023]    It is advantageous to control MPEG picture decoding order based on knowledge of where the pictures start and stop in the video bit buffer. Thus knowledge of picture location in the video bit buffer  60 B allows memory start pointers in the start code detector  520  and variable length detector  531  to be directed to effectively randomly access pictures from the video bit buffer as required, for example, during trick mode operation. Operation at reverse at play speed and or slow motion playback requires the reproduction of B-frames. Such reverse mode operation may be advantageously simplified in terms of buffer memory requirements by reversing the order in which adjacent B pictures are decoded. This reversal of decoding order is achieved by setting the memory start pointers to enable decoding of the picture required by the trick mode. In addition buffer memory size and control may be simplified during trick play operation by advantageously skipping or not reading pictures in the video bit buffer as required by specific trick play algorithms. Trick play buffer memory size and control may be advantageously optimized by enabling multiple decoding of pictures either immediately or as specifically required by the trick play algorithm. The facilitation of these advantageous features requires careful control of read/write functions and the synchronization therebetween.  
         [0024]    The block diagram of FIG. 4 shows the same functions and element numbering as depicted in FIG. 2, however, FIG. 4 includes additional advantageous arrangements which will be explained. The exemplary digital video disk player shown in FIGS. 2, 3 and  4  may be considered to comprise two parts namely a front end and a back end. The front end controls the disk and transducer with the back end providing MPEG decoding and overall control. Such functional partitioning may represent an obvious solution for consistent, steady state, MPEG decoding. However, such partitioning of processing with control from the back end may result in microcontroller overload, for example, during trick mode operation and particularly in the reverse direction.  
         [0025]    In FIG. 4 control data is transmitted by an I 2 C control bus  514 , which communicates the next wanted replay sector address to servo control system  50 . The next wanted replay sector address is generated by microcontroller  510  which processes address data originating from a stored trick play, speed specific sequence, replayed and stored navigation data, or from advantageously determined replayed picture data. The next address is read from the I 2 C bus and stored in element  53 . The I 2 C data also includes an advantageous end/last sector address, or first unwanted sector address. The end/last sector address may be obtained from recovered and stored navigation data, however this provides only a limited number of predetermined picture addresses, thus for trick modes the advantageously determined end of picture sector addresses are employed. The end/last sector address is read from the I 2 C bus and stored in element  52 . The last sector address may modified either prior to bus transmission or upon receipt, to prevent wanted sector loss, by for example, the addition of one unit count to sector address thus ensuring addressing and detection of the first unwanted sector. The last sector address, or modified address  52 A is coupled for comparison with the replay sector address signal  42  in an exemplary comparator  51 . Thus, when the replay sector address  42  equals address  52 A, the first unwanted sector is about to be transduced and comparator  51  generates control signal  51 A. Control signal  51 A enables coupling from element  53 , for example by loading or shifting the stored address data to the servo, or as depicted by exemplary selector switch  54  which couples the next sector address to the servo system and initiates repositioning of transducer  15 . As has been described, the transducer is moved to the track containing the next wanted picture and data output signal  41  is advantageously enabled by element  43  when the wanted picture is reproduced.  
         [0026]    The transducer continues to follow the track reproducing wanted sectors which are processed by the back end. In response to data recovered from these sectors a new pair of next and end sector addresses are generated and transmitted via the I 2 C bus. These new address are received and stored as before in elements  52  and  53 . However to avoid initiating a transducer jump before the new end sector address is replayed and detected by element  51 , exemplary selector  54  is reset or opened preventing premature initiation and acquisition of the new sector address.  
         [0027]    A further advantageous arrangement recognizes that control requirements differ between operational modes and such differences can be beneficially exploited to allow processor time to be directed to trick mode specific tasks. Hence microcontroller interrupts, both internal and external to the microcontroller are assigned different or reordered priorities, and or inhibited in accordance with the operational mode. Such mode specific interrupt prioritization can reduce or eliminate wasted CPU time servicing inconsequential interrupts or requests rendered irrelevant by playback mode selection.  
         [0028]    For example, during normal play speed operation CPU  510  is generally concerned with obtaining and decoding data to form the next picture required for display and as such the sequence of events is largely determined by the display rate. Clearly audio data acquisition and decoding have similar CPU timing or priority needs. Responsiveness to user control commands is important but of lower CPU importance that a temporally smooth, non-repeated flow of pictures. The provision of sub pictures in response to user selection is of yet lower CPU importance but clearly the system must not impose an unacceptable user delay.  
         [0029]    The various trick replay modes generally have control requirements that differ from each other and from normal play operation. For example slow motion in a forward direction poses few control problems since the required extra pictures can be provided by controllably repeating the current display picture and decoding a new picture when the currently displayed picture is to be changed. Since audio is not required, decoding is inhibited, but the audio buffer is emptied occasionally to prevent the generation of an overflow interrupt which, although irrelevant wastes processor time.  
         [0030]    In a fast forward trick mode CPU timing and control become important, for example at twice speed the decoding frame rate must be increased with certain decoded pictures being discarded or not displayed from the display buffer. In trick mode operation the display memory control and decode complete flags are no longer locked to the frame rate hence the controller must respond more quickly. To achieve the exemplary speedup, the display processor may need to display fields instead of frames. Thus interrupts need to run twice as fast (2× frame rate) and in addition certain pictures, for example B pictures from the display buffer will be skipped. The start code detector must to be started faster and earlier than the display rate in order to find and either discard compressed pictures or decode them at a rate faster than they are displayed. In addition processor time can not be spent emptying the audio buffer since the data is not decoded and the buffer interrupt wastes processor time, thus audio interrupts can be inhibited.  
         [0031]    The various MPEG buffer memories must be monitored closely and their fullness maintained since data is flowing faster than during normal play operation. In addition buffer control can be assigned an opposite polarity than normal MPEG processing, since during forward play operation the input or track buffer is kept from overflowing, however in trick modes an underflow condition is more likely to occur. However, at some point the buffers will become empty and data is lost terminating the current decoding process. Decoding is then resumed by jumping ahead to the next I-picture. In addition the user may attempt to find a specific scene by changing or varying replay rates and direction, hence user command priorities must be processed promptly requiring a higher interrupt priority than slow or play speed operation.  
         [0032]    Thus it can be appreciated that the entire CPU system dynamics are different with trick mode operation and changing interrupt priorities can more effectively accommodate the trick mode features, shutting down some interrupts like audio, and sub-picture processing, increasing the MPEG buffer interrupt priority, and lowering the buffer full flag from the front end can help the system process data during trick mode operation.  
         [0033]    Reverse trick modes, and in particular reverse play speed operation, is exceptionally problematic since often the same picture data is acquired and decoded multiple times to construct reference pictures that are temporally too early to be displayed. The controller can become sufficiently taxed that servicing interrupts may limit the performance.  
         [0034]    The microcontroller  510 , of FIGS. 2, 3 and  4  is advantageously controlled in response to user selected replay mode, for example, play, fast forward, reverse, such that interrupts coupled to the microcontroller are assigned different priorities depending on the selected operating mode. Microcontroller  510 , for example an ST Microelectronics type ST 20 , allows either internal or external interrupt signals to interrupt a currently running CPU process. This exemplary microcontroller facilitates the prioritization of interrupts by use of an interrupt controller and interrupt level controller. The interrupt level controller is controlled by software which determines or controls multiplexing of the incoming interrupts onto eight interrupt inputs of the interrupt controller. Advantageously, a selected operating mode, play, fast forward, reverse, ect., which is executed by the microcontroller is also employed to select different control software for coupling to determine the multiplexing of incoming interrupt requests to prioritized inputs of the interrupt controller. Thus external interrupt inputs can be multiplexed to achieve a reordered input sequence when coupled to the priority controller. In this way certain external interrupt signals are dynamically assigned interrupt priority levels which change in response to the selected replay modes.  
         [0035]    The software control of interrupt priorities in response to play back mode is shown TABLE 1 with examples of selector and multiplexor  551  reordering external interrupt signals (irt(n)) between interrupt inputs (μC  0 - 7 ) of interrupt controller  560 , in accordance with three exemplary reproducing modes.  
         [0036]    In the following table (TABLE 2) exemplary parameters are shown associated with microcontroller  510 . However, these various exemplary assignments and reassignments of priority, are determined not only by the complexities of MPEG trick mode decoding, but also with regard to the specific requirements of the subject microcontroller. For example, in TABLE 2 it is apparent that remote control decoding, IR/PWM is maintained with the highest interrupt priority regardless of the selected reproduction mode. This requirement is specific to the microcontroller in which buffer memory capacity for I.R. remote control instructions is small, consequently to maintain user control and prevent interrupt hang-ups the interrupt is assigned the highest priority.  
                           TABLE 2                           S1   S2   S3       μC   PLAY   For nX   Rev nX                   0   IR/PWM   IR/PWM   IR/PWM       1   Input DMA full   video decode   video decode       2   video decode   Input DMA full   I 2 C       3   audio decode   OSD   OSD       4   sub-pic. decode   audio decode   Input DMA full       5   cc inter   I 2 C   audio decode       6   OSD   cc inter   cc inter       7   I 2 C   sub-pic. decode   sub-pic. decode                  
 
         [0037]    The following nomenclature is used in TABLE 2:  
         [0038]    IR/PWM=Infra red, pulse width modulated control code.  
         [0039]    Input DMA full=indication of full state in exemplary track buffer  60 A.  
         [0040]    Video decode=MPEG video decoder interrupt request.  
         [0041]    Audio decode=MPEG/AC3 audio decoder interrupt request.  
         [0042]    Sub-pic. Decode=MPEG sub-picture decoder interrupt request.  
         [0043]    Cc inter.=closed caption interrupt request decoded from the MPEG stream.  
         [0044]    OSD=on screen display, player system request.  
         [0045]    I 2 C=Inter integrated circuit bus.  
         [0046]    The hierarchical nature the MPEG signal necessitates that I and P frames are decoded in a forward direction, thus reverse mode reproduction can be facilitated by jumping back to an earlier, or preceding I frame and then decoding, possibly multiple times in a forward direction through that GOP. Clearly these trick mode complexities discussed herein are not confined to digital video disk reproduction and are equally applicable to other storage media, such as hard disks, recordable disks etc. The inventive reassignment of CPU interrupt priorities permits the optimization of CPU processing time during MPEG trick mode operation from any storage medium.  
         [0047]    [0047]FIG. 5 depicts exemplary control sequences for microcontroller  510  that permit the assignment of different interrupt priorities in accordance with selected operating modes. At block  100  of FIG. 5, mode dependent interrupt priority assignment is initiated. A test is performed at step  200  to determine if the selected operating condition is a normal PLAY mode, a YES results in the acquisition of a software program  1  from a memory location. Software program  1  (S 1 ) is applied to select multiplexor  550  (SEL MUX) and determines coupling or routing, provided by multiplexor  551 , of external interrupt request signals (irt(n)) to prioritized inputs of interrupt controller  560 .  
         [0048]    If step  200  tests NO, a further test is performed at block  300  to determine if a fast forward (FOR nX) reproduction mode has been selected, for example 6X. A YES causes software program  2 , (S 2 ) to be acquired from memory and coupled to multiplexor  550  to determine the coupling of external interrupt signals by multiplexor  551  to the prioritized inputs of interrupt controller  560 .  
         [0049]    However if step  300  tests NO, a further test is performed at block  400  to determine if a REVERSE (REV nX) reproduction mode has been selected, for example −3X. As described previously a YES causes software program  3  (S 3 ) to be coupled to determine the setting of multiplexor  550  and thus the coupling of external interrupt signals to interrupt controller  560 . If step  400  tests NO the sequence returns to block  200  which initiates a loop that monitors for the selection of ones of the plurality of reproducing modes such that an optimum predetermined interrupt priority is selected specific to the chosen operating mode. The advantageous recognition of differing control requirements during different operational modes beneficially allows processor time to be directed to trick mode specific tasks which facilitate temporally smoother image presentation.