Broadcom BCM5722 - Figure 5: Transmit Data Path; Transmit Data Path; Tx Fifo; Tx Mac

BCM5722 Programmer’s Guide
10/15/07
Broadcom Corporation
Page 17 Transmit Data Path Document 5722-PG101-R
TRANSMIT DATA PATH
TX MAC
The Read DMA engine moves packets from host memory into internal NIC memory (see Figure 5). When the entire packet
is available, the transmit MAC is activated.
Figure 5: 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