The present invention provides systems and methods for adaptive digital data transmission rate control. A digital data transmission system for adaptively transferring packets over a transmission link includes a client device having a bandwidth control module and a host device coupled to the client device over the transmission link. The host device includes one or more bandwidth control registers and a packet builder. The bandwidth control module determines a packet speed and/or size for packets transmitted from the host device to the client device over the transmission link. The bandwidth control registers store the requested packet size and/or rate. The packet builder accesses these registers when transmitting packets to determine the requested packet size and/or rate.