High Performance Two Port 10/100 Managed Ethernet Switch with
Datasheet
Chapter 6 Switch Fabric
6.1Functional Overview
At the core of the LAN9312 is the high performance, high efficiency 3 port Ethernet switch fabric. The switch fabric contains a 3 port VLAN layer 2 switch engine that supports untagged, VLAN tagged, and priority tagged frames. The switch fabric provides an extensive feature set which includes spanning tree protocol support, multicast packet filtering and Quality of Service (QoS) packet prioritization by VLAN tag, destination address, port default value or DIFFSERV/TOS, allowing for a range of prioritization implementations. 32K of buffer RAM allows for the storage of multiple packets while forwarding operations are completed, and a 1K entry forwarding table provides room for MAC address forwarding tables. Each port is allocated a cluster of 4 dynamic QoS queues which allow each queue size to grow and shrink with traffic, effectively utilizing all available memory. This memory is managed dynamically via the buffer manager block within the switch fabric. All aspects of the switch fabric are managed via the switch fabric configuration and status registers (CSR), which are indirectly accessible via the memory mapped system control and status registers.
The switch fabric consists of four major block types:
Switch Fabric CSRs - These registers provide access to various switch fabric parameters for configuration and monitoring.
10/100 Ethernet MACs - A total of three MACs are included in the switch fabric which provide basic 10/100 Ethernet functionality for each switch fabric port.
Switch Engine (SWE) - This block is the core of the switch fabric and provides VLAN layer 2 switching for all three switch ports.
Buffer Manager (BM) - This block provides control of the free buffer space, transmit queues, and scheduling.
Refer to Figure 2.1 Internal LAN9312 Block Diagram on page 21 for details on the interconnection of the switch fabric blocks within the LAN9312.
6.2Switch Fabric CSRs
The switch fabric CSRs provide register level access to the various parameters of the switch fabric. Switch fabric related registers can be classified into two main categories based upon their method of access: direct and indirect.
The directly accessible switch fabric registers are part of the main system CSRs of the LAN9312 and are detailed in Section 14.2.6, "Switch Fabric," on page 229. These registers provide switch fabric manual flow control (Ports
The indirectly accessible switch fabric registers reside within the switch fabric and must be accessed indirectly via the Switch Fabric CSR Interface Data Register (SWITCH_CSR_DATA) and Switch Fabric CSR Interface Command Register (SWITCH_CSR_CMD), or the set of Switch Fabric CSR Interface Direct Data Register (SWITCH_CSR_DIRECT_DATA). The indirectly accessible switch fabric CSRs provide full access to the many configurable parameters of the switch engine, buffer manager, and each switch port. The switch fabric CSRs are detailed in Section 14.5, "Switch Fabric Control and Status Registers," on page 307.
For detailed descriptions of all switch fabric related registers, refer to Chapter 14, "Register Descriptions," on page 166.
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