The General Control Packet (GCP) is primarily handled by the hardware but is also passed to the software so that the information can be used at the system application level.
typedef struct XHdmiC_GCP_Packet {
unsigned char Set_AVMUTE;
unsigned char Clear_AVMUTE;
XHdmiC_ColorDepth ColorDepth;
XHdmiC_PixelPackingPhase PixelPackingPhase;
unsigned char Default_Phase;
} XHdmiC_GeneralControlPacket;