Transmit Data Path
BCM5718 Programmer’s Guide
Broadcom
®
January 29, 2016 • 5718-PG108-R
Page 56
Transmit Data Path
TX MAC
The Read DMA engine moves packets from host memory into internal NIC memory (see
). When the
entire packet is available, the transmit MAC is activated.
Figure 4: Transmit Data Path
The transmit MAC is responsible for the following functions:
• Moving data from NIC internal memory into TX FIFO
• Moving data from TX FIFO to PHY
• Checksum substitutions (not calculation)
• Updating statistics
TX FIFO
The TX FIFO provides elasticity while data is moved from device internal memory to PHY. There are no
programmable settings for the TX FIFO. This FIFO’s operation is completely transparent to host software.
TX
MAC
Consumer
Index
Update
Tx
FIFO
Send BD
NIC Send Ring Cache
Select Send BDs
(SBDs) from Send
Ring
Host Send Producer Rings
DMA
DMA
TX Data
TX Data
TX Data
TX Data
TX Data
TX Data
TX Data
TX Data
Buffer0
Buffer1
Buffer2
Buffer3
Buffer4
Buffer5