CN112492240B

CN112492240B - Method for identifying clock frequency of HDMI audio return signal

Info

Publication number: CN112492240B
Application number: CN201910856683.3A
Authority: CN
Inventors: 李冰; 周寿华
Original assignee: Individual
Current assignee: Hefei Hanxin Technology Co ltd
Priority date: 2019-09-11
Filing date: 2019-09-11
Publication date: 2022-06-28
Anticipated expiration: 2039-09-11
Also published as: CN112492240A

Abstract

The invention discloses a method for identifying the clock frequency of an HDMI audio return signal, which comprises the following steps: determining a plurality of sampling frequencies of the audio return signal, each sampling frequency corresponding to and being N times a clock frequency of the audio return signal; and identifying the clock frequency of the audio return signal, sampling the audio return signal by using the sampling frequency, and judging whether the sampling frequency corresponds to the audio return signal according to the number of beats sampled from the audio return signal between two adjacent jump delays.

Description

Method for identifying clock frequency of HDMI audio return signal

Technical Field

The invention relates to the technical field of optical communication. In particular, the present invention relates to a method for HDMI audio return signal clock frequency discrimination.

Background

The HDMI (High Definition Multimedia Interface) protocol specification is now already the de facto "optimal" solution for civilian-grade (alternatively referred to as consumer-grade) High-Definition Multimedia transmission.

With the increasing requirements of the HDMI protocol version upgrading and the transmission distance increasing, the requirements of optical cable transmission, especially the technology of pure optical cable transmission HDMI signals, are more and more urgent.

In the HDMI protocol signals, four high-speed signals are provided and are responsible for unidirectional audio and video transmission; there are also low speed signals, which are responsible for processing hot plug detection HDMI HPD signals such as handshaking, consumer electronics control HDMI CEC signals such as remote control shared, display data channel HDMI DDC signals for basic information exchange identification of two-end devices, audio return HDMI ARC signals.

Existing HDMI signal transmission uses an all-copper cable. According to the latest HDMI 2.1 specification, the HDMI high-speed signal rate has reached 48Gbps, and at such a high rate, the transmission of electrical signals between devices should be regarded as microwave signal transmission, and the corresponding transmission medium is a transmission line, so that the complete transmission of signals can be ensured without signal loss such as reflection, and thus, the due high-definition pictures and sound effects can be clearly and unmistakably displayed on the display device. Unfortunately, however, the cost of the transmission line fabrication, as the length increases, is an order of magnitude increase, which is catastrophic for HDMI for consumer applications. That is, the conventional HDMI all-copper cable is not suitable for the solution of HDMI transmission over long distance (generally 10 m to 300 m).

This situation is very similar to the situation encountered in earlier telecommunications systems where broadband to the home is encountered, again as the signal rate increases, copper has not been a good solution. There is a statement in the telecommunications system of "optical copper in and out". Therefore, in the long-distance transmission of HDMI, a high-speed signal can be transmitted by an optical cable. Two branch solutions are derived as such: hybrid cables and pure fiber optic cables.

The HDMI hybrid cable, i.e., the solution of optical fiber + copper cable, transmits high-speed signals with optical fiber in cooperation with four-channel photoelectric conversion chips, and other low-speed signals are transmitted by using traditional copper cables. The optical fiber and copper wire are placed in the same cable. Thus, the long-distance transmission of high-speed signals is perfectly solved. The presence of copper cables in long-distance hybrid cables still causes a large burden in cost. In addition, it causes a lot of inconvenience in application, such as a hybrid cable more than one hundred meters long, heavy weight, and great pressure on storage, transportation, and engineering wiring. In addition, although low speed signals are available, signal distortion and attenuation over long distances can be severe, especially for HDMI DDC and ARC signals.

In contrast, the advantages of the pure optical cable (all signals are transmitted by optical fiber) solution for HDMI long-distance transmission are more prominent. At long distances, the cost of optical fiber has a greater advantage over copper wire. And the pure optical fiber cable material under the same length is lighter and more portable, and the wiring is more convenient. And the optical fiber transmission signal has no problems of deformation and attenuation.

In the solution of pure optical fiber cable, the low-speed signals are generally time-division multiplexed and then transmitted by a pair of optical fibers (transmitting and receiving). However, in the protocol of HDMI ARC, there are three ARC clock frequencies, i.e., 4.096MHz, 5.6448MHz, 6.144MHz, and it is necessary to perform clock frequency discrimination on the ARC signal at the time of multiplexing in order to perform sampling and transmission of the ARC signal with an appropriate clock signal.

Therefore, the development of a digital algorithm for clock frequency discrimination of the HDMI ARC signal is urgently needed in the art.

Disclosure of Invention

The invention aims to correctly identify the transmission frequency of an audio return signal sent by HDMI SINK (receiving) end equipment, so as to ensure that an HDMI low-speed signal processing digital circuit (or DgtlCore) correctly identifies and transmits an ARC signal to HDMI SOURCE (SOURCE) equipment.

According to an aspect of the present invention, there is provided a method for HDMI audio backhaul signal clock frequency discrimination, comprising:

determining a plurality of sampling frequencies of the audio return signal, each sampling frequency corresponding to and being N times a clock frequency of the audio return signal; and

and identifying the clock frequency of the audio return signal, sampling the audio return signal by using the sampling frequency, and judging whether the sampling frequency corresponds to the audio return signal according to the number of beats sampled from the audio return signal between two adjacent jump delays.

In one embodiment of the present invention, there are three audio return signal clock frequencies, one for each audio return signal clock frequency.

In one embodiment of the present invention, whether the current sampling frequency is N times the clock frequency of the audio return signal is tried by polling collision.

In an embodiment of the present invention, the clock frequencies of the three audio return signals are 4.096MHz, 5.6448MHz, and 6.144MHz, respectively, and the corresponding sampling frequencies are 49.152MHz, 67.7376MHz, and 73.728MHz, respectively.

In one embodiment of the invention, the sampling frequency is 12 times the audio return signal clock frequency.

In one embodiment of the invention, performing the discrimination of the clock frequency of the audio backtransmission signal comprises monitoring a state in which it is monitored whether the number of beats sampled on the audio backtransmission signal between two adjacent transition delays is equal to any one of N +1, N and N-1, if the number of beats sampled on the audio backtransmission signal between two adjacent transition delays is equal to any one of N +1, N and N-1, where N e [1,3], the sampling frequency corresponds to the audio backtransmission signal, otherwise the sampling frequency does not correspond to the audio backtransmission signal.

In one embodiment of the invention, the identifying the clock frequency of the audio return signal comprises entering a search/verify state when the number of beats sampled on the audio return signal between two adjacent transition delays is not equal to any one of N +1, N, and N-1, combining small windows between M groups of adjacent transition edges of the audio return signal into a large window in the search/verify state, sampling and verifying whether the number of beats of the M groups of adjacent transition edges is equal to any one of N +1, N, and N-1, N ∈ [1,3], M is an integer greater than or equal to 1, if the number of beats of the M groups of adjacent transition edges is equal to any one of N +1, N ∈ [ N ], and N-1, the current sampling frequency corresponds to the audio return signal, switching the current sampling frequency if at least one of the beat counts of the M sets of adjacent hop edges is not equal to any of N x N +1, N x N, and N x N-1.

In one embodiment of the present invention, M-8.

In one embodiment of the invention, switching the current sampling frequency is performed in a cyclic order of 73.728MHz, 67.7376MHz, 49.152MHz, 73.728MHz, ….

In one embodiment of the invention, when the sampling frequency is determined to correspond to the audio return signal, the audio return signal clock frequency is determined based on the sampling frequency to complete the sampling and transmission of the HDMI audio return signal in the pure cable scheme.

Drawings

To further clarify the above and other advantages and features of embodiments of the present invention, a more particular description of embodiments of the invention will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings, the same or corresponding parts will be denoted by the same or similar reference numerals for clarity.

Fig. 1 illustrates a flow diagram of a method for HDMI audio return ARC signal clock frequency discrimination according to one embodiment of the present invention.

Figure 2 illustrates a 12-fold relationship of the ARC clock frequency and the ARC sampling clock frequency according to one embodiment of the present invention.

Detailed Description

In the following description, the present invention is described with reference to various embodiments. One skilled in the relevant art will recognize, however, that the embodiments may be practiced without one or more of the specific details, or with other alternative and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the embodiments of the invention. However, the invention may be practiced without specific details. Further, it should be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

Reference in the specification to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

The invention provides a method for HDMI ARC signal clock frequency discrimination, which comprises the determination of three sampling clock frequencies corresponding to three ARC clock frequencies and a clock frequency discrimination method. The determination of the sampling clock frequency needs to consider the three clock frequencies of the HDMI ARC signal and the characteristics of the BMC code pattern thereof, and can distinguish the three ARC clock frequencies by the sampling beat number of the HDMI ARC signal to the long connection '0'/'1'. The clock frequency identification method monitors whether the sampled HDMI ARC signal corresponds to the current sampling clock frequency or not at any moment, and if so, keeps the current sampling clock frequency; and if not, performing large-window verification according to a further verification algorithm to determine whether the sampling frequency is really required to be switched.

By adopting the digital circuit, ARC signals at the HDMI SINK end are sampled to carry out ARC BMC code pattern bit identification; after the identification, the framing is carried out; each frame is sequentially and serially output and sent to a laser driver (a sending end of an optical signal transceiver) for electro-optical conversion, so that the encapsulated ARC signal is sent to an HDMI SOURCE end; the receiving end of the SOURCE end optical signal transceiver receives an optical signal, converts the optical signal into an electric signal, and sends the ARC to an ARC PIN PIN at the HDMI interface side according to a fixed time sequence through the frame decoding function of the DgtlCore. To complete the sampling and transmission of HDMI ARC signals in a pure cable scheme.

Fig. 1 illustrates a flow diagram of a method for HDMI audio return ARC signal clock frequency discrimination according to one embodiment of the present invention. The ARC clock frequency in HDMI applications may also be referred to as BMC frequency, fbmc _ clk. The BMC is a signal encoded with the ARC signal, and the frequency of the BMC is the ARC clock frequency.

First, at step 110, the sampling frequency of the audio return ARC signal is determined. In the protocol of HDMI ARC, there are three ARC clock frequencies, i.e., 4.096MHz, 5.6448MHz, 6.144 MHz. According to the characteristics of the ARC BMC code pattern, the longest length of the connection '0'/'1' of the BMC code pattern is 3 bits, so that three ARC clock frequencies respectively correspond to one sampling frequency, and the sampling frequencies are required to distinguish the three ARC frequencies after sampling the ARC BMC code pattern. The principle of distinction is to see if the number of beats N0 sampled on the ARC signal between two adjacent transition delays (i.e. the number of beats sampled in conjunction with '0'/'1') matches the eigenvalue. It is verified that 49.152MHz, 67.7376MHz, and 73.728MHz are the minimum sampling frequency fs _ ARC of the three ARC clock frequencies, respectively, and can distinguish the three ARC clock frequencies, i.e. 12 multiples of each ARC clock frequency. Higher frequency multiplication is certainly satisfactory and the eigenvalues are more significant, but 12 frequency multiplication is more appropriate considering that the power consumption of the digital circuit is proportional to the clock frequency.

Figure 2 illustrates a 12-fold relationship of the ARC clock frequency and the ARC sampling clock frequency according to one embodiment of the invention. As shown in FIG. 2, the ARC signal has a clock frequency of 6.144MHz, the BMC code is 1 bit with 0, the sampling frequency fs _ ARC of the ARC signal is 73.728MHz, and the possible values of the number of beats N0 sampled by the ARC signal with two sampling points x falling exactly between two adjacent transition delays are: 11, where both x are considered to be "1"; 12, where one of the two x is considered to be "1"; 13, where both x are considered to be "0".

Table 1 below shows the values of N0 (obtained by sampling three ARC frequencies respectively) and their characteristic values for three ARC sampling frequencies according to one embodiment of the present invention.

TABLE 1

In table 1, the hatched numbers represent characteristic values indicating that the current sampling frequency fs _ arc is maintained.

Whereas the unshaded numbers indicate that it may be necessary to switch the sampling frequency fs _ arc.

After determining the sampling frequency of the audio return ARC signal, at step 120, a discrimination of the HDMI ARC signal clock frequency is performed.

The identification of the HDMI ARC clock frequency disclosed by the invention comprises the searching and switching of the sampling clock frequency, and whether the current sampling frequency fs _ ARC is 12 times of the ARC clock frequency is tried in a polling collision mode. The discrimination of the HDMI ARC signal clock frequency comprises two states: monitoring status and search/verify status.

In the monitoring state, the sampling beat number (denoted as N0) of the current clock to ARC between two adjacent transition edges (small window) is monitored:

if N0 +1, N12 or N12-1, N e [1,3] is satisfied, then the current clock is deemed to be corresponding or appropriate; the state machine does not jump;

if not, the current clk is considered to be "possibly" not applicable, and a search mechanism is required to be started for verification; the state machine jumps to the search/verify state.

In the search/verification state, combining small windows among M groups of adjacent transition edges into a large window, sampling and verifying whether the M times of N0 respectively satisfy N0 ═ N × 12+1, N × 12 or N × 12-1, N ∈ 1,3, and M is an integer greater than or equal to 1. In one embodiment of the invention, M is 8, but other values are possible, simply by increasing the width of the filter, or the width of the large window.

If all of the M times satisfy N0 ═ N × 12+1, N × 12, or N × 12-1, no switching frequency is required;

if the M times of verification are not satisfied, the frequency is required to be switched;

then, regardless of the comparison result, the state machine is switched to a monitoring state, and the process is circulated;

in one embodiment of the invention, the switching frequency may be performed in a cyclic sequence of 73.728MHz, 67.7376MHz, 49.152MHz, 73.728MHz, …. However, those skilled in the art will appreciate that the scope of the present invention is not limited in this respect, and that other frequency switching sequences may be employed in other embodiments of the present invention.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various combinations, modifications, and changes can be made thereto without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A method for HDMI audio return signal clock frequency discrimination, comprising:

identifying the clock frequency of the audio return signal, sampling the audio return signal by using the sampling frequency, and judging whether the sampling frequency corresponds to the audio return signal according to the number of beats sampled from the audio return signal between two adjacent jumping edges;

determining an audio return signal clock frequency based on the sampling frequency when the sampling frequency is determined to correspond to the audio return signal,

Wherein, three audio return signal clock frequencies exist, each audio return signal clock frequency corresponds to a sampling frequency, whether the current sampling frequency is N times of the audio return signal clock frequency is tried in a polling collision mode,

wherein the identifying the clock frequency of the audio return signal comprises monitoring a state in which it is monitored whether the number of beats sampled from the audio return signal between two adjacent edges is equal to any of N +1, N and N-1, if the number of beats sampled from the audio return signal between two adjacent edges is equal to any of N +1, N and N-1, where N is e [1,3], then the sampling frequency corresponds to the audio return signal, otherwise the sampling frequency does not correspond to the audio return signal,

wherein, the identification of the clock frequency of the audio return signal comprises a searching/verifying state, when the number of beats sampled to the audio return signal between two adjacent jumping edges is not equal to any one of N + N, N and N-1, the audio return signal enters the searching/verifying state, in the searching/verifying state, small windows between M groups of adjacent jumping edges of the audio return signal are combined into a large window, the number of beats of the M groups of adjacent jumping edges is sampled and verified whether to be respectively equal to any one of N + N, N and N-1, N [1,3], M is an integer which is larger than or equal to 1, if the number of beats of the M groups of adjacent jumping edges is equal to any one of N + N +1, N and N-1, the current sampling frequency corresponds to the audio return signal, if at least one of the M groups of adjacent jumping edges is not equal to N +1, N and N-1, the current sampling frequency corresponds to the audio return signal, and if at least one of the number of beats of the M groups of adjacent jumping edges is not equal to N +1, N and N-1, the current sampling frequency is switched.

2. The method of claim 1, wherein the three audio return signal clock frequencies are 4.096MHz, 5.6448MHz, 6.144MHz, respectively, and the corresponding sampling frequencies are 49.152MHz, 67.7376MHz, 73.728MHz, respectively.

3. The method for HDMI audio return signal clock frequency discrimination as recited in claim 1, wherein said sampling frequency is 12 times the audio return signal clock frequency.

4. The method for HDMI audio return signal clock frequency discrimination of claim 1, wherein M-8.

5. The method for HDMI audio return signal clock frequency discrimination of claim 1, wherein switching the current sampling frequency is performed in a cyclic sequence of 73.728MHz, 67.7376MHz, 49.152MHz, 73.728MHz ….