Patent Application
20080005401
1. Technical Field of the Invention
The present invention relates to buffer controller as may be used in codecs and related methods.
2. Description of Related Art
As is known, codecs are used in a wide variety of electronic devices that process real-time signals such as audio and/or video signals. Such devices include laptop, notebook and other personal computers, personal digital assistants (PDA), compact disk (CD) players, Motion Picture Experts Group (MPEG3) or (MP3) players, digital video disk (DVD) players, amplitude modulation/frequency modulation (AM/FM) radios, satellite radios, cellular telephones, etc. As an example, a computer may include an audio codec integrated circuit to support the processing of audio signals in order to produce an audio output that is delivered to the user through speakers, headphones or the like and a video codec for playing streaming video or DVD video content on the computer's display screen.
Codecs typically include a buffer to support the processing of the real-time signal. When multiple real-time signals are present, multiple buffers are required. The need exists for codecs that can be efficiently implemented in an integrated circuit environment.
Further, computer 100 includes a video codec 109 for processing video signals derived from streaming video, stored video files in a digital video format such as MPEG1, MPEG2, MPEG4 or other digital video format, or played from a DVD for display on the display screen of computer 100.
Audio codec 108 and/or video codec 109 include various features and functions in accordance with the present invention that will be described in conjunction with the figures that follow.
In an embodiment of the present invention, codec 150 is an audio codec such as codec 108 and the first real-time signal is an audio signal and the sequence of samples can be 24-bit samples of an audio signal at a sampling frequency such as 44 kHz, and pulse code modulated, however, greater or lesser bit accuracy such as 16 bits or 32 bits can likewise be used, other modulation schemes and differing sample frequencies may also be employed. In an embodiment of the present invention, codec 150 is a video codec such as video codec 109 and real-time signal 110 is a video signal.
Output modules 140 and 142 are operably coupled to the buffer memory 120, memory arbitration module 122 and the buffer controller 125. Output modules 140 and 142 are each operable for reading a sequence of read locations in the buffer memory as directed by corresponding read pointers generated by buffer controller 125. In an embodiment of the present invention output modules 140 and/or 142 can include digital to analog converters that produce outputs 141 and 143, such as an analog audio output, from the buffered sequence of samples. While two output modules 140 and 142 are shown, a greater number of output modules can likewise be coupled to buffer controller 125. In this fashion, multiple output modules 140, 142, etc., can access real-time signal 110 via a multiple access buffer structure implemented by buffer controller 125. Further details regarding the implementation of buffer controller 125 including additional functions and features are presented in association with the figures that follow.
In an embodiment of the present invention, memory arbitration module 122 controls access to the buffer memory by the input module 130 and the output modules 140 and 142. Memory arbitration module 122 receives write requests from input module 130 and sends acknowledgements to input module 130 when a sample can be written to the buffer memory 120. Similarly, memory arbitration module 122 receives read requests from output modules 140 and 142 and sends acknowledgements to the output module 140 when a sample can be read from the buffer memory 120.
Read enable module 204 receives read enable signals from any of the output modules 140, 140′, 142, 142′, etc. to determine which of the output modules are coupled to read the buffered sequence of samples from the corresponding input module 130. Buffer controller 125, in turn, generates read pointers 212 and status signals 216 in response to the received read signals 214 and the write pointer 218, for each of the output modules that have supplied read enable signals 210. In an embodiment of the present invention, read pointer generation module 200 automatically generates read pointers 212 for output modules 140, 140′, 142, 142′, etc., even when the read enable signal for a particular output module is deasserted. In this case, the read pointer is advanced when all remaining read pointers 212 have been advanced. This simplifies the operation of status generation module 202 since it can assess all of the read pointers 212 without first checking which read enable signals 210 are asserted. Further, this embodiment provides the advantage that all the read pointers 212 are updated. If an output module comes on-line and sets its read enable signal 210, the corresponding read pointer 212 is ready.
Buffer controller 125 further includes read pointer generation module 200 for generating a plurality of read pointers 212, wherein each of the first plurality of read pointers points to a sequence of read locations in the buffer memory, in a buffer order such as first-in first-out, that contain the sequence of samples of real-time signal 110. As the samples are read from buffer memory, read pointer generation module 200 directs the output modules 140, 142, etc. to the next locations to be read from the buffer memory 120.
In operation, when a particular output module completes a read operation that reads the location in the buffer memory corresponding to the read pointer 212, the output module generates a read signal 214 that triggers read pointer generation module 200 to update the read pointer 212, (in a fashion similar to the updating of the write pointer as previously described) that corresponds to that particular output module.
In this fashion, each of the output modules 140, 142, etc. can independently access the buffer memory and the sequence of samples of real-time signal 110. Read pointer generation module updates each of the read pointers 212 independently based on the read status of each output modules 140, 142, etc.
In an embodiment of the present invention, buffer controller 125 further includes a status generation module 202, operably coupled to the buffer memory and the first read pointer generation module, for determining a status for each of the first plurality of output modules. In particular, the status generation module determines a ready state, an overflow state and an underflow state for each of the output modules 140, 142, etc. with respect to the buffer. The status generation module 202 is further operable to determine if the buffer memory 120 is in an empty state or a full state. Status generation module is capable of generating a status signal to output modules 140, 142, etc., that indicates the state to further control the buffering process. In an embodiment of the present invention, the status signal is a 3-bit digital signal having unique digital values for empty, full, ready, underflow and overflow; however other signaling schemes may likewise be employed within the broad scope of the present invention.
In an embodiment, the status generation module 202 determines an empty state and generates a status signal corresponding to an empty signal when a particular output module has read each of the sequence of samples stored in the buffer memory and the input module has not stored the next sample. This is the case when the read pointer generation module updates the read pointer 212 for that particular output module to a value that matches the value of write pointer 218. In an embodiment of the present invention, one or more of the output modules 140, 142, etc., is an asynchronous module that, in response to a empty status signal, decelerates its read operations from the buffer, such as by executing an interrupt that begins one or more read operations at a later time, or by decreasing the clock frequency driving the read operations of the particular output module for a period or time in order to avoid “getting ahead” of the input module 130. In an embodiment of the present invention, the particular output module responds to the empty signal by muting its corresponding output—such as by producing an output signal corresponding to ground, a direct current (DC) level or otherwise producing an output signal without an audio or video component.
Likewise when the status generation module 202 determines that a output module has overflowed the buffer by the input module 130 overwriting a buffer location with a new sample value prior to the old sample value being read by the particular output module, or underflowing the buffer by an output module reading a buffer location prior to the location being written with the current sample of the real-time signal 110, the status generation module responds by generating a status signal corresponding to either an overflow signal or an underflow signal, depending on the case. In an embodiment of the present invention, the particular output module responds to the overflow and underflow signals by also muting its corresponding output.
When the status generation module 202 determines a full state, when the input module 130 has written to the last available buffer location for a particular output module i.e. the write pointer 218 is one location behind the read pointer 212 for that particular output module), a full signal is generated. In an embodiment of the present invention one or more of the output modules 140, 142, etc., is an asynchronous module that, in response to a full status signal, accelerates its read operations from the buffer, such as by executing an interrupt that begins one or more read operations early, or by increasing the clock frequency driving the read operations of the particular output module for a period or time in order to reduce the back-log of unread samples. Alternatively, for output modules 140, 142, etc., that are synchronous modules, these output modules mute their corresponding output if the status progresses to an overflow condition, as discussed above.
In an embodiment of the present invention, the ready status is determined for a particular output module and a ready signal is generated when none of the empty, full, overflow or underflow conditions apply. In an embodiment of the present invention, during start-up conditions, an empty status signal is generated and the output modules 140, 142, etc., are muted in response. When the output modules 140, 142, etc., begin reading samples from the buffer, the status is changed to ready.
In an embodiment of the present invention, the empty, full, overflow, underflow and ready signals are generated to each of the output modules based on their particular status. In other words, at any given time, each of these signals is generated to the particular subset of all output modules (from all to none) that this particular signal status currently applies. However, in an embodiment of the present invention, the status of any of the output modules 140, 142, etc. in the empty, full, overflow or underflow status causes the status generation module 202 to generate a corresponding status signal 212 to all of the output modules 140, 142 coupled to buffer controller 125.
In an embodiment of the present invention, buffer controller 125 can be implemented using a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions that are stored in memory. The memory may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the processing module implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Further note that, in an embodiment of the present invention operation instructions are stored in locations of buffer memory 120 that are reserved for this purpose and not used for storing samples of the real-time input-signals 110, 110′, etc.
While operation of buffer controller 125 has been described, buffer controller 125′ can operate similarly in accordance with one or more of the alternative embodiments described herein.
In an embodiment of the present invention, n=16 is used, however greater or lesser value can be used within the broad scope of the present invention, based upon the amount of buffering required, the amount of signal latency that can be tolerated, etc. In the event that multiple buffer controllers 125, 125′, etc. are implemented, a plurality of separate buffer locations are reserved for each buffer controller. The multiple buffers may be of the same size or of different sizes, particularly if the sample rate varies for different output modules 140, 142, 140′, 142′ etc. Each of the output modules 140, 142, etc., coupled to a single input module 130 operate with generally the same sample rate. A different input module 130′, and the output modules 140′, 142′ etc. coupled thereto may operate at a different sample rate.
In an embodiment of the present invention, each of the first plurality of read pointers includes a base address in the buffer memory and a pointer address in the buffer memory. Each of the first plurality of read pointers has a plurality of least significant bits and a plurality of most significant bits, wherein the pointer address is included in the least significant bits and the base address is included in the most significant bits such that each of the plurality of read pointers is a physical memory address. In an embodiment, the buffer order is first-in first-out and the real-time signal is either an audio signal or a video signal. Further in an embodiment, step 402 includes updating one of the first plurality of read pointers when a corresponding one of the first plurality of output modules completes a read operation from the buffer memory.
In an embodiment of the present invention, during start-up conditions, an empty status signal is generated. The first plurality output modules are muted in response, until step 404 when the first plurality output modules begin reading the first sequence of read locations from the buffer.
As one of ordinary skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As one of ordinary skill in the art will further appreciate, the term “operably coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of ordinary skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “operably coupled”. As one of ordinary skill in the art will further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1.
In preferred embodiments, the various circuit components are implemented using 0.35 micron or smaller CMOS technology. Provided however that other circuit technologies including other transistor, diode and resistive logic, both integrated or non-integrated, may be used within the broad scope of the present invention. Likewise, various embodiments described herein can also be implemented as software programs running on a computer processor. It should also be noted that the software implementations of the present invention can be stored on a tangible storage medium such as a magnetic or optical disk, read-only memory or random access memory and also be produced as an article of manufacture.
As the term module is used in the description of the various embodiments of the present invention, a module includes a functional block that is implemented in hardware, software, and/or firmware that performs one or multiple functions such as the processing of an input signal to produce an output signal. As used herein, a module may contain submodules that themselves are modules.
Thus, there has been described herein an apparatus and method, as well as several embodiments including a preferred embodiment, for implementing a codec and buffer controller. Various embodiments of the present invention herein-described have features that distinguish the present invention from the prior art.
It will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than the preferred forms specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope of the invention.
