AUDIO TRANSMISSION SYSTEM AND SLAVE DEVICE

1 . An audio transmission system performing time-division multiplexing on audio data of N channels (N is an integral number equal to or larger than 1) for each reference period and transmitting multiplexed audio data, the N channels representing a number of channels determined in advance in accordance with a preset mode, the audio transmission system comprising:

a master circuit;

one or more slave circuits connected to the master circuit via one or more transmission lines by daisy chain topology; and

a signal processing circuit, wherein

each piece of audio data of the N channels corresponds to a different one of the one or more slave circuits, the each piece of audio data of the N channels being assigned to a different one of N transmission/reception periods obtained by time-dividing the reference period,

each of the one or more slave circuits includes a register to store a mode value representing the preset mode,

the master circuit writes the mode value onto the register included in the each of the one or more slave circuits,

the each of the one or more slave circuits

generates a bit clock in accordance with the mode value stored in the register, the bit clock being synchronized with a clock of data to be transmitted or received via the one or more transmission lines, and

serially transmits or receives a corresponding piece of audio data out of pieces of audio data of the N channels to/from the master circuit in the transmission/reception period assigned to the corresponding piece of audio data,

either one of the master circuit and the one or more slave circuits function as an audio transmitter to transmit audio data, and the other one function as an audio receiver to receive audio data, and

the signal processing circuit limits a level of audio data of the N channels to be equal to or smaller than a predetermined value in a case where a level of audio data received by the audio receiver is larger than a threshold value.

2 . The audio transmission system according to claim 1 , wherein

the master circuit transmits a synchronization signal synchronized with the reference period to the each of the one or more slave circuits via the one or more transmission lines, and

the each of the one or more slave circuits generates the bit clock in accordance with the mode value stored in the register and the synchronization signal.

3 . The audio transmission system according to claim 2 , wherein the each of the one or more slave circuits changes a frequency of the bit clock in accordance with the mode value stored in the register.

4 . The audio transmission system according to claim 3 , wherein

the master circuit functions as the audio receiver,

the each of the one or more slave circuits functions as the audio transmitter, and

the signal processing circuit limits the level of audio data of the N channels to be equal to or smaller than a predetermined value in a case where a level of a piece of audio data of the N channels received by the master circuit is larger than the threshold value.

5 . The audio transmission system according to claim 4 , further comprising an output circuit, wherein

the signal processing circuit performs audio signal processing on the each piece of audio data of the N channels received by the master circuit, and

the output circuit

receives the each piece of audio data of the N channels from the signal processing circuit,

performs digital-to-analog conversion on respective pieces of audio data of the N channels to generate audio signals of N channels, and

causes a speaker to output each of the generated audio signals of N channels.

6 . The audio transmission system according to claim 5 , further comprising a communication circuit that transmits/receives data to/from an information processing device via a communication bus,

wherein the communication circuit

acquires, from the output circuit, audio data of at least one channel out of audio data of the N channels, and

transmits the audio data acquired from the output circuit to the information processing device via the communication bus.

7 . The audio transmission system according to claim 4 , further comprising microphones, wherein

the each piece of audio data of the N channels represents audio collected by one of the microphones.

8 . The audio transmission system according to claim 7 , further comprising one or more analog-to-digital converters,

wherein each of the one or more analog-to-digital converters

corresponds to one or more of the microphones,

performs analog-to-digital conversion on an audio signal output from each of the corresponding one or more of the microphones at each sampling timing to generate one or more pieces of audio data synchronized with the bit clock at each sampling timing, and

gives one or more pieces of the generated audio data to a corresponding one of the one or more slave circuits.

9 . The audio transmission system according to claim 3 , wherein

the master circuit functions as the audio transmitter,

each of the one or more slave circuits functions as the audio receiver,

the signal processing circuit is provided correspondingly to each of the one or more slave circuits, and

the signal processing circuit limits a level of audio data received by a corresponding one of the one or more slave circuits to be equal to or smaller than a predetermined value in a case where the level of the received audio data is larger than the threshold value.

10 . The audio transmission system according to claim 9 , further comprising one or more output circuits that are provided correspondingly to the one or more slave circuits, wherein

the signal processing circuits performs audio signal processing on the audio data received by the corresponding slave circuit, and

each of the one or more output circuits

receives audio data from the signal processing circuit of a corresponding one of the one or more slave circuits,

performs digital-to-analog conversion on the received audio data to generate an audio signal, and

causes a speaker to output the generated audio signal.

11 . An audio transmission system performing time-division multiplexing on audio data of N channels (N is an integral number equal to or larger than 1) for each reference period and transmitting multiplexed audio data, the N channels representing a number of channels determined in advance in accordance with a preset mode, the audio transmission system comprising:

a master circuit;

one or more slave circuits connected to the master circuit via one or more transmission lines by daisy chain topology; and

one or more stop circuits corresponding to the one or more slave circuits, wherein

each piece of audio data of the N channels corresponds to a different one of the one or more slave circuits, the each piece of audio data of the N channels being assigned to a different one of N transmission/reception periods obtained by time-dividing the reference period,

each of the one or more slave circuits includes a register to store a mode value representing the preset mode,

the master circuit writes the mode value onto the register included in the each of the one or more slave circuits,

the each of the one or more slave circuits

generates a bit clock in accordance with the mode value stored in the register, the bit clock being synchronized with a clock of data to be transmitted or received via the one or more transmission lines, and

serially transmits a corresponding piece of audio data out of pieces of audio data of the N channels to the master circuit in the transmission/reception period assigned to the corresponding piece of audio data, and

each of the one or more stop circuits causes a corresponding one of the one or more slave circuits to stop transmission of audio data to the master circuit in a case where a frequency of the bit clock generated by the corresponding slave circuit falls outside a frequency range set in advance.

12 . A slave device in an audio transmission system, the audio transmission system including a master device and one or more slave devices connected to the master device via one or more transmission lines by daisy chain topology, the slave device comprising:

a slave circuit; and

a stop circuit, wherein

the audio transmission system performs time-division multiplexing on audio data of N channels (N is an integral number equal to or larger than 1) for each reference period and transmits multiplexed audio data, the N channels representing a number of channels determined in advance in accordance with a preset mode,

each piece of audio data of the N channels corresponds to a different one of the one or more slave circuits, the each piece of audio data of the N channels being assigned to a different one of N transmission/reception periods obtained by time-dividing the reference period,

the slave circuit includes a register to store a mode value representing the preset mode,

the master device writes the mode value onto the register,

the slave circuit

generates a bit clock in accordance with the mode value stored in the register, the bit clock being synchronized with a clock of data to be transmitted or received via the one or more transmission lines, and

serially transmits a corresponding piece of audio data of out of pieces of audio data of the N channels to the master device in the transmission/reception period assigned to the corresponding piece of audio data, and

the stop circuit causes the slave circuit to stop transmission of audio data to the master device in a case where a frequency of the bit clock generated by the slave circuit falls outside a frequency range set in advance.