Abstract: A method and apparatus for configuring a cyclic redundancy check (CRC) generation circuit to perform CRC on a data stream are disclosed. The method includes storing a generator polynomial associated with a CRC equation in a register, where the generator polynomial has a length capable of varying such that the length has any value less than or equal to a number of bits associated with a CRC generation circuit. A bit position of the CRC generation circuit that corresponds to the length of the generator polynomial is selected by using a first multiplexer to generate a feedback value. The CRC generation circuit is programmed to calculate a CRC checksum based on the generator polynomial stored in the register and the feedback value from the selected bit position.

Abstract: A digital device having selectable modes for USB communications buffer management in a USB interface of the digital device. These modes may comprise (1) no ping-pong buffer support, (2) ping-pong buffer support for some endpoints, e.g., support for OUT endpoint 0 only, and (3) ping-pong buffer support for all endpoints. In the no ping-pong buffer support mode, no hardware is required for automatic ping-pong buffer management. The Buffer Descriptor Tables may comprise a maximum of 128 memory locations, e.g., 16 IN endpoints and 16 OUT endpoints, each with at least one buffer descriptor, and each comprising four (4) memory locations. In the ping-pong buffer support for OUT endpoint 0 only mode, the buffer descriptor Tables may comprise a maximum of 132 memory locations, e.g., 16 OUT endpoints with an EVEN and an ODD endpoint 0, 16 IN endpoints, each with at least one descriptor, e.g., memory locations.