Abstract: A host controller can be used in transferring data over a USB bus communication system in frames and micro-frames. Each data transfer is described by a packet transfer descriptor, and a packet transfer descriptor for a data transfer includes a bit map, such that data is transferred according to the packet transfer descriptor only during those micro-frames of a frame which correspond to bits of the bit map for which the bit value has been set to an active value.

Abstract: A method of transferring bulk and control data from a first device to a second device over a USB bus comprises storing transfer descriptors, each including a transfer descriptor header and payload data, in a buffer memory in the first device. The data is read in packets for transfer to the second device, with packets being read from the transfer descriptors cyclically. When the first and second transfer descriptor headers, in first and second transfer descriptors respectively, define a common endpoint, data packets are read from only the first transfer descriptor, until such time as it is detected that all data packets from the first transfer descriptor have been transmitted, and thereafter data packets are read from the second transfer descriptor.