Increased Bluetooth Clock Accuracy

Abstract

The present invention provides a communications unit for operation in a communication system in accordance with a protocol that operates to a first clock resolution, the communications unit comprising a first clock, operating to the first resolution, a second clock operating to a second resolution higher than the first resolution, means configured to respond to a request to report a clock value by reporting: (a) the current value of the first clock and (b) information indicating the time on the second clock at which the first clock ticked to its current value.

What is claimed is: 
     
         1 . A device capable of operating according to a wireless communications protocol, the device comprising:
 a first clock; the device being configured to:
 receive media from another device, determine a play out time for playing out the received media in dependence on the first clock, and 
 send, in accordance with the wireless communications protocol, the media and play out time to a second device. 
   
     
     
         2 . A device as claimed in  claim 1 , wherein the device is configured to send a clock signal representing a time on the first clock to the second device. 
     
     
         3 . A device as claimed in  claim 1 , wherein the media is received in accordance with the wireless communications protocol. 
     
     
         4 . A device as claimed in  claim 1 , wherein the wireless communications protocol is a Bluetooth protocol. 
     
     
         5 . A device as claimed in  claim 4 , wherein the clock is a Bluetooth master clock. 
     
     
         6 . A device as claimed in  claim 1 , wherein the device is configured to play the media at the play out time. 
     
     
         7 . A device as claimed in  claim 1 , wherein the device comprises a speaker for playing out the media. 
     
     
         8 . A device as claimed in  claim 1 , wherein the media and play out time are sent together. 
     
     
         9 . A device as claimed in  claim 1 , wherein the media and play out time are sent separately. 
     
     
         10 . A device as claimed in  claim 1 , wherein the first clock operates to a first resolution, the device further comprising a second clock operating to a second resolution higher than the first resolution, the play out time being determined additionally in dependence on the second clock. 
     
     
         11 . A device as claimed in  claim 1 , wherein the device is further configured to adjust a playback rate for the media in dependence on the play out time and a time determined in dependence on the first clock and the second clock. 
     
     
         12 . A communications system comprising:
 a first device configured to send media to a second device;   the second device comprising a first clock and being capable of operating according to a wireless communications protocol and being configured to:
 receive media from the first device, 
 determine a play out time for playing out the received media in dependence on the first clock, and 
 send, in accordance with the wireless communications protocol, the media and the play out time to a third device; 
   a third device capable of operating according to the wireless communications protocol and being configured to:
 receive the media and play out time from the second device, and 
 play the media received from the second device at the play out time. 
   
     
     
         13 . A communications system as claimed in  claim 12 , wherein the second device is further configured to play the media received from the first device at the play out time. 
     
     
         14 . A communications system as claimed in  claim 12 , wherein the second device is configured to send a clock signal representing a time on the first clock, the play out time for the received media being determined in dependence on the first clock. 
     
     
         15 . A communications system as claimed in  claim 14 , wherein the third device is configured to:
 receive the clock signal, and   maintain a representation of the first clock in dependence on the received clock signal, wherein the media is played out at the play out time according to the maintained representation of the first clock.   
     
     
         16 . A communications system as claimed in  claim 12 , wherein the communication system is a Bluetooth communications system. 
     
     
         17 . A communications system as claimed in  claim 12 , wherein the first clock is a Bluetooth network master clock. 
     
     
         18 . A method comprising, at a first device:
 receiving media from another device;   sending a clock signal representing a time on a first clock to a second device;   determining a play out time for playing out the received media in dependence on the first clock; and   sending the media and the play out time to the second device.   
     
     
         19 . A method as claimed in  claim 18 , further comprising, at the second device:
 receiving the media and the play out time from the first device; and   playing the media received from the first device at the play out time.   
     
     
         20 . A method as claimed in  claim 18 , the method further comprising, at the first device, playing the media received from said another device at the play out time.