Method and device to transfer a video stream between a host device and an electronic descrambling device

A method to descramble at least one video stream, originating from at least one producer having a producer ID, by an electronic descrambling device connected to a host device, said host device comprising a controller configured for bulk out and bulk in transfers, comprising:

• in the host device,
• for the at least one producer, defining multiple chunks of data from the video stream;
• forming a chain out transfer structure, the chain out transfer structure comprising a chain out header linked with a plurality of chain out descriptors, a first chain out descriptor pointing to an out description packet containing the producer ID of the at least one producer, second and subsequent chain out descriptors pointing to respective scrambled chunks of data, each scrambled chunk of data corresponding to the producer ID of the first chain out descriptor and originating from the at least one producer associated with the producer ID of the first chain out descriptor;
• transferring the chain out transfer structure, including the chain out header and the plurality of chain out descriptors pointing respectively to the producer ID and the respective scrambled chunks of data, by the controller to the electronic descrambling device;
• at the electronic descrambling device,
• receiving the chain out transfer structure, including the out description packet by the electronic descrambling device and identifying by the electronic descrambling device key data associated with the scrambled chunks of data;
• using the key data to descramble the scrambled chunks of data;
• returning the descrambled chunks of data to the host device;
• at the host device,
• receiving a chain in transfer structure by the controller, from the electronic descrambling device, the chain in transfer structure including a chain in header linked with a plurality of chain in descriptors, each chain in descriptor pointing to a descrambled chunk of data, and a last chain in descriptor being configured to generate an interrupt;
• storing each of the received descrambled chunks of data from the chain in transfer structure at an address indicated by the corresponding chain in descriptor;
• and
• triggering an interrupt in response to reception of the last chain in descriptor.