
MVTX2802
Data Sheet
17
Zarlink Semiconductor Inc.
2.3.1 Ethernet Frames
The CPU interface is also responsible for receiving and transmitting standard Ethernet frames to and from the
CPU. To transmit a frame from the CPU:
The CPU writes a “data frame” register (address 011) with the data it wants to transmit. After writing all the
data, it then writes the frame size, destination port number, and frame status.
The MVTX2802AG forwards the Ethernet frame to the desired destination port, no longer distinguishing the
fact that the frame originated from the CPU.
To receive a frame into the CPU:
The CPU receives an interrupt when an Ethernet frame is available to be received.
Frame information arrives first in the data frame register. This includes source port number, frame size, and
VLAN tag.
The actual data follows the frame information. The CPU uses the frame size information to read the frame
out.
In summary, receiving and transmitting frames to and from the CPU is a simple process that uses one direct
access register only.
2.3.2
Control Frames
In addition to standard Ethernet frames described in the preceding section, the CPU is also called upon to
handle special “Control frames,” generated by the MVTX2802AG and sent to the CPU. These proprietary
frames are related to such tasks as statistics collection, MAC address learning, aging, etc. All Control frames
are 64 bytes long. Transmitting and receiving these frames is similar to transmitting and receiving Ethernet
frames, except that the register accessed is the “Control frame data” register (address 110).
Specifically, there are eight types of control frames generated by the CPU and sent to the MVTX2802AG:
Memory read request
Memory write request
Learn MAC address
Delete MAC address
Search MAC address
Learn IP Multicast address
Delete IP Multicast address
Search IP Multicast address
Note:
Memory read and write requests by the CPU may include VLAN table, spanning tree, statistic counters, and
similar updates.
In addition, there are nine types of Control Frames generated by the MVTX2802AG and sent to the CPU:
Interrupt CPU when statistics counter rolls over
Response to memory read request from CPU
Learn MAC address
Delete MAC address
Delete IP Multicast address
New VLAN port
Age out VLAN port
Response to search MAC address request from CPU
Response to search IP Multicast address request from CPU