The controller can be programmed to perform IP, TCP, and UDP checksum offloading in both receive and transmit directions, enabled by setting bit  in the network configuration register for receive, and bit  in the DMA configuration register for transmit.
IPv4 packets contain a 16-bit checksum field, which is the 16-bit 1's complement of the 1's complement sum of all 16-bit words in the header. TCP and UDP packets contain a 16-bit checksum field, which is the 16-bit 1's complement of the 1's complement sum of all 16-bit words in the header, the data, and a conceptual IP pseudo header.
Calculating these checksums in software requires each byte of the packet to be processed. For TCP and UDP a large amount of processing power can deter the process. Offloading the checksum calculation to the GEM controller can result in significant performance improvements.
For IP, TCP, or UDP checksum offload to be useful, the operating system containing the protocol stack must be aware that this offload is available for the GEM controller to either generate or verify the checksum.
Note: To enable the controller, compute the proper checksum needed by the system software to ensure that the checksum fields are initialized to 0.