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Devices are waiting for GVCP packets listening to the GVCP port (3956). When the client sends a command GVCP packet to the device, the device sends back an acknowledge packets in return. Each command/acknowledge pair is identified by a 16 bit value, which allows to check if an acknowledge packet corresponds to the previsoulsy sent command. 0 is an error value for this identifier. If an acknowledge is not received after a given timeout period, another command packet is sent, until a maximum number of retries is reached.
The content of a GVCP packet is composed by a 64 bit headers, followed or not by a data byte array, depending on the GVCP packet type. Multibyte values are in big endian encoding.
A device discovery mechanism is implemented using a discovery GVCP packet, broadcasted by the client to the GVCP port. Each available device responds to this discovery packet with an acknowledge packet, containing a description of the device (device name, model name, manufacturer name, MAC Address...).
These packets are used for the read and write of 32 bit registers, accessed using 32 bit adresses. For the read command, a list of addresses is sent ot the client, which returns a list of 32 bit values. For the write command, a list of address/value pairs is sent to the client, which returns a list of 32 bit values.
Address and data are encoded in the packet as big endian values.