Camera control interface slave device to slave device communication

Abstract

In a shared bus where communications are managed by a master device, direct slave device to slave device (S2S) communications is implemented. A first slave device wanting to communicate with a second slave device may make a S2S communication request to the master device. The request may include a requested number of words that the first slave device wishes to send over the shared bus. The master device may have a current word limit which may vary based upon operating parameters. The master device may deny the request if the requested number of words is greater than the current word limit or if it does not support S2S communications. Denial of the request may also be for other reasons, like activity over the shared bus. If the master device grants the request, the slave device may send the requested number of words to another slave device over the shared bus.

What is claimed is: 
     
         1 . A master device, comprising:
 a bus interface circuit to couple to a control data bus shared with a plurality of slave devices; and   a processing circuit coupled to the bus interface circuit and configured to:
 control access to the control data bus by the plurality of slave devices; 
 receive a request from a slave device for access to the control data bus for slave device to slave device communication; 
 grant or deny the request received from the slave device; and 
 after granting the request, permit the slave to use the control data bus for direct data transfer between the slave device and another slave device of the plurality of slave devices, without transmitting the data transferred during the direct data transfer. 
   
     
     
         2 . The master device of  claim 1 , wherein the slave device to slave device communication request includes a requested number of words to be transferred by the requesting slave device to another slave device. 
     
     
         3 . The master device of  claim 1 , wherein the slave device to slave device communication request includes a requested maximum number of words to be transferred from the requesting slave device to another slave device over the control data bus; and the processing circuit is further configured to:
 send, to the requesting slave device, a response granting the request.   
     
     
         4 . The master device of  claim 3 , wherein the response grants the request by including a word limit number in the response that is equal to or greater than the maximum number of words included in the request. 
     
     
         5 . The master device of  claim 3 , wherein the processing circuit is configured to:
 monitor the control data bus to detect an end of slave device to slave device communications; and   regain control of the control data bus after an end of slave device to slave device communications is detected.   
     
     
         6 . The master device of  claim 1 , wherein the slave device to slave device communication request includes a requested maximum number of words to be transferred from the requesting slave device to another slave device over the control data bus; and the processing circuit is further configured to:
 send, to the requesting slave device, a response denying the request.   
     
     
         7 . The master device of  claim 6 , wherein the slave device to slave device communication request is denied if the requested maximum number of words is greater than a current word limit of the master device. 
     
     
         8 . The master device of  claim 6 , wherein the processing circuit is further configured to:
 send, to the requesting slave device, a response denying the request by sending an acceptable number of words when the requested maximum number of words provided by the requesting slave device is greater than a current word limit.   
     
     
         9 . The master device of  claim 6 , wherein the master device sends the response denying the request if the master device does not support slave device to slave device communications. 
     
     
         10 . A method operational by a master device, comprising:
 controlling access to a control data bus shared with a plurality of slave devices;   receiving a request from a slave device for access to the control data bus for slave device to slave device communication;   granting or denying the request from the slave device; and   after granting the request, permitting the slave to use the control data bus for direct data transfer between the slave device and another slave device of the plurality of slave devices, without transmitting the data transferred during the direct data transfer.   
     
     
         11 . The method of  claim 10 , wherein the slave device to slave device communication request includes a requested maximum number of words to be transferred from the requesting slave device to another slave device over the control data bus. 
     
     
         12 . The method of  claim 11 , further comprising:
 sending, to the requesting slave device, a response granting the request.   
     
     
         13 . The method of  claim 12 , further comprising:
 monitoring the control data bus to detect an end of slave device to slave device communications; and   regaining control of the control data bus after an end of slave device to slave device communications is detected.   
     
     
         14 . The method of  claim 11 , further comprising:
 sending, to the requesting slave device, a response denying the request.   
     
     
         15 . The method of  claim 14 , further comprising:
 receiving a request from the requesting slave device to have the master device transfer a certain amount of information between the requesting slave device and the another slave device; and   transferring data between the requested information between the requesting slave device and the another slave device.   
     
     
         16 . The method of  claim 14 , wherein the response denying the request includes an acceptable number of words that is less than the requested maximum number of words. 
     
     
         17 . A slave device, comprising:
 a bus interface circuit to couple to a control data bus shared with a plurality of slave devices and a master device; and   a processing circuit coupled to the bus interface circuit and configured to:
 send a slave device to slave device communication request over the control data bus to the master device; 
 receive a response granting or denying the request from the master device; and 
 after receiving a response granting the request, use the control data bus for direct data transfer between the slave device and another slave device of the plurality of slave devices in which data is transferred between the slave device and another slave device without being transmitted by the master device. 
   
     
     
         18 . The slave device of  claim 17 , wherein the communication request includes a requested maximum number of words to be transmitted by the slave device to another slave device over the control data bus. 
     
     
         19 . The slave device of  claim 18 , wherein the processing circuit is further configured to:
 receive a response denying the request from the master device.   
     
     
         20 . The slave device of  claim 19 , wherein the response includes an otherwise acceptable number of words from the master device. 
     
     
         21 . The slave device of  claim 20 , wherein the processing circuit is further configured to:
 send a new slave device to slave device communication request to the master device, wherein the new slave device to slave device communication request includes a new requested maximum number of words that is less than or equal to the acceptable number of words.   
     
     
         22 . The slave device of  claim 19 , wherein the processing circuit is further configured to:
 send a new request to have the master device transfer a certain amount of information between the requesting slave device and the another slave device.   
     
     
         23 . The slave device of  claim 19 , wherein the processing circuit is further configured to either:
 resend the same slave device to slave device communication request, with the same maximum number of words, to the master device at a later time; or   send a new slave device to slave device communication request with a second word limit that is less than the previous maximum word limit requested but greater than an acceptable number of words identified by the master device in its denial of the initial request.   
     
     
         24 . The slave device of  claim 19 , wherein the processing circuit is further configured to:
 send a master request to the master device to transfer control of the control data bus to the requesting slave device;   operate as new master of the control data bus if the master request is granted by the master device; and   send a desired amount of data words to another slave device.   
     
     
         25 . The slave device of  claim 17 , wherein the processing circuit is further configured to:
 receive the response granting the request; and   send a slave device to slave device communication to the control data bus.   
     
     
         26 . The slave device of  claim 17 , wherein the slave device to slave device communication is limited to an acceptable number of words approved by the master device. 
     
     
         27 . A method operational on a slave device coupled to a control data bus shared with a plurality of slave devices and a master device, comprising:
 sending a slave device to slave device communication request over the control data bus to the master device;   receiving a response granting or denying the request from the master device; and   after receiving a response granting the request, using the control data bus for direct data transfer between the slave device and another slave device of the plurality of slave devices in which data is transferred between the slave device and another slave device without being transmitted by the master device.   
     
     
         28 . The method of  claim 27 , wherein the slave device to slave device communication request includes a requested number of words to be transferred by the slave device to another device over the control data bus. 
     
     
         29 . The method of  claim 27 , further comprising:
 receiving the response granting the request; and   sending a slave device to slave device communication to the control data bus.   
     
     
         30 . The method of  claim 29 , wherein the slave device to slave device communication is limited to an acceptable number of words approved by the master device.