Large Segment OffloadBCM5718 Programmer’s Guide
Broadcom®
January 29, 2016 • 5718-PG108-R Page 115
The driver should zero the TCP checksum field in the offloaded TCP packet, but leave the IP checksum alone.
This requirement may change with newer NetXtreme controllers.
Broadcom drivers enable long burst by default in the Read DMA Mode register (0x4800 bits 17:16 = 11 binary
= 4k byte burst size).
Do not set TxFIFO Underrun Prevention Enable (bit 31) in the Buffer Manager Mode register 0x4400.
Do not set bit 5 (Multiple Segment Enable) in 0xC00 (Send Data Initiator Mode register).
Example TCP-segmentation-related (LSO) register values
Source: Broadcom tg3 Linux driver with BCM5764M NIC
0x4800 08033BFE Read DMA Mode Register
0x0C00 0000000A Send Data Initiator Mode Register
0x0CF4 50000020 Pre-DMA Command Exchange for Segmentation
0x0CEC 00040028 DMA Flag Register for TCP Segmentation
0x1008 A0000000 Pre-DMA Command Exchange for Segmentation
0x0CE8 00000036 Length/Offset Register for Segmentation
0x0CF0 00000000 VLAN Tag Register for TCP Segmentation
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