Low latency serial bus

A method, comprising:

• setting an isochronous cycle timer to provide a cycle frame that is no more than 50 microseconds in duration;
• generating an isochronous packet;
• transmitting the isochronous packet in the cycle frame;
• transmitting a cycle start packet responsive to expiration of the isochronous cycle timer, wherein the cycle start packet includes:
• a cycles/8000 field;
• a cycle count field;
• and
• a cycle offset field;
• and
• adding, in a physical layer control circuit, a repeater delay value to a cycle offset value.

An active noise cancellation (ANC) system, comprising:

• a microphone wherein the microphone converts a first group of sound waves into a first audio digital signal;
• a speaker wherein the speaker receives a second audio digital signal and converts the second audio digital signal into a second group of sound waves;
• and
• an ANC controller coupled to the microphone and the speaker by a serial bus, in which the ANC controller includes a link layer control circuit configured to control isochronous data transfer between the ANC controller, the microphone, and the speaker over the serial bus, and the link layer control circuit includes an isochronous cycle timer configured to provide a cycle frame that is less than 125 microseconds in duration;
• wherein the link layer control circuit is configured to generate an isochronous packet for transfer in the cycle frame, the isochronous packet including no more than eight header bytes, the header bytes including:
• a 4-bit data length field encoding a packet payload length in octlets;
• a 12-bit time offset field;
• a 4-bit format field;
• and
• a 4-byte header check field.

A serial bus control circuit comprising:

• a link layer control circuit configured to control isochronous data transfer over a serial bus, the link layer control circuit including:
• an isochronous cycle timer configured to provide a cycle frame that is less than 125 microseconds in duration;
• a physical layer control circuit coupled to the link layer control circuit;
• wherein:
• the link layer control circuit is configured to:
• generate a cycle start packet including:
• a cycles/8000 field;
• a cycle count field;
• and
• a cycle offset field;
• transmit the cycle start packet to start the cycle frame;
• and
• the physical layer control circuit is configured to add a repeater delay value to a cycle offset value stored in the cycle offset field of the cycle of a received cycle start packet.

A method, comprising:

• setting an isochronous cycle timer to provide a cycle frame that is no more than 50 microseconds in duration;
• generating an isochronous packet having a header including no more than eight bytes, the header including:
• a 4-bit data length field encoding a packet payload length in octlets;
• a 12-bit time offset field;
• a 4-bit format field;
• and
• a 4-byte header check field;
• and
• transmitting the isochronous packet in the cycle frame.

An active noise cancellation (ANC) system, comprising:

• a microphone wherein the microphone converts a first group of sound waves into a first audio digital signal;
• a speaker wherein the speaker receives a second audio digital signal and converts the second audio signal into a second group of sound waves;
• and
• an ANC controller coupled to the microphone and the speaker by a serial bus, in which the ANC controller includes a link layer control circuit configured to:
• control isochronous data transfer between the ANC controller, the microphone, and the speaker over the serial bus, and
• generate a cycle start packet including:
• a cycles/8000 field;
• a cycle count field;
• and
• a cycle offset fields;
• and
• wherein the link layer control circuit includes an isochronous cycle timer configured to provide a cycle frame that is less than 125 microseconds in duration.