MDS212 Datasheet, PDF (47/111 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps Ethernet Switch

MDS212
Data Sheet
The port will serve the next job from the Transmission Scheduling queue when the following two conditions are met:
• There is room for a 1.5Kbyte frame (a maximum-sized frame) within the TxFIFO.
• The end-of-frame (EOF) of the current frame has arrived at the TxFIFO.
There are four transmission-scheduling queues for each port, one for each of the four classes of priority. The port
will send the jobs to the transmission scheduling queues according to a first in first out (FIFO) order.
To start data transmission, the port obtains a job from the transmission scheduling queue and notifies the Transmit
DMA (TxDMA) to move the data from the FDB to the MAC Transmit FIFO (TxFIFO) in 128-byte granules (for local
forwarding). Otherwise, the device sends a DATA_REQ command message via the XPipe to the source device to
request remote forwarding. The data forwarding engine module in the Frame Engine of the source device will then
forward the frame in 128-byte granules via the XPipe.
12.1.3 Multicast Frame Forwarding
After the reception of the switching response, a job is sent to the Transmission Scheduling queues of the
destination ports for local switching. However, for remote switching, one copy of the frame will be forwarded to the
remote device in 128-byte granules via the XPipe. This copy of the frame will be sent to the frame data buffer. The
Frame Engine, after the successful reception of this frame, will put jobs in the Transmission Scheduling queues of
the destination ports of its device. When the TxFIFO is ready to receive the frame (same as the conditions stated in
unicast frame forwarding section), the TxDMA will forward the frame from the FDB to the destination ports in
granule form. The maximum size of a granule is 128 bytes.
12.2 Flow For Data Frame
The following subsections describe the flow of information during transfers of data frames, both unicast and
multicast.
12.2.1 Unicast Data Frame To Local Device
In the simplest case, the data frame is destined for a port on the local device. The Frame Engine moves the
received frame to the local FDB. The Search Engine forms a switch request with the frame header (includes source
MAC and Destination MAC) and passes it to the Switch Engine to resolve the destination. The Switch Engine then
provides a destination port address to the Frame Engine via a switch response message. The Frame Engine
transmits to put a transmission job in transmission scheduling. After the port is ready to send the frame, the Frame
Engine starts to move the frame to the TxFIFO. If the MAC address cannot be resolved by the Switch Engine, the
HISC and/or the CPU are queried to resolve the address. For an unknown destination MAC, the frame will flood the
frame into the source VLAN domain.
12.2.2 Unicast Data Frame To Remote Device
In another case, the data frame is destined for a port on a remote device. First, the Frame Engine moves the
received frame to the local FDB. A switch request with a frame header (includes source MAC and Destination MAC)
is passed to the Switch Engine to resolve the destination. The Switch Engine then provides a destination port
address to the Frame Engine. If the address resolution cannot be completed by the Switch Engine, the HISC and/or
the CPU are queried. Once the address is resolved, the two Frame Engines perform the following interactive
handshaking procedures via the XPipe:
• Source Frame Engine sends a Data Forwarding Request message to Destination, where the destination
Frame Engine puts a job in the associated transmission scheduling queue.
• When the destination port is ready to send the frame, the destination Frame Engine send a Data Request
message to the source Frame Engine.
• After the source Frame Engine receives the Data Request Message, it starts to move the frame in granule
form, which is directly written in the destination TxFIFO.
47
Zarlink Semiconductor Inc.