Intel IXF1104 Packet Buffer Dimensions, Rmon Statistics Support, TX and RX Fifo Operation TX Fifo

Intel® IXF1104 4-Port Gigabit Ethernet Media Access Controller

5.1.7Packet Buffer Dimensions

5.1.7.1TX and RX FIFO Operation

5.1.7.1.1TX FIFO

The IXF1104 MAC TX FIFOs are implemented with 10 KB for each channel. This provides enough space for at least one maximum size (10 KB) packet per-port storage and ensures that no under-run conditions occur, assuming that the sending device can supply data at the required data rate.

A transfer to MAC Threshold parameter, which is user-programmable, determines when the FIFO signals to the MAC that it has data to send. This is configured for specific block sizes, and the user must ensure that an under-run does not occur. Also, the threshold can be set above the maximum size of a normal Ethernet packet. This causes the FIFO to send only data to the MAC when this threshold is exceeded or when the End-of-Packet marker is received. This second condition eliminates the possibility of under-run, except when the controlling switch device fails. It can, however, cause idle times on the media.

5.1.7.1.2RX FIFO

The IXF1104 MAC RX FIFOs are provisioned so that each port has its own 32 KB of memory space. This is enough memory to ensure that there is never an over-run on any channel while transferring normal Ethernet frame size data.

The FIFOs automatically generate Pause control frames to halt the link partner when the High watermark is reached and to restart the link partner when the data stored in the FIFO falls below the low-watermark. The RX and TX FIFOs have been sized to support lossless flow control with

9.6 KB packets. The RX FIFO has a programmable transfer threshold that sets the threshold at which packets become “cut through” and starts transitioning to the SPI3 interface before the EOP is received. Packets sizes below this threshold are treated as “store and forward.” Once a packet size exceeds the RX FIFO transfer threshold, it can no longer be dropped by the RX FIFO even if it is marked to be dropped by the MAC.

5.1.8RMON Statistics Support

The IXF1104 MAC supplies RMON statistics through the CPU interface. These statistics are available in the form of counter values that can be accessed at specific addresses in the register maps (Table 59 through Table 69). Once read, these counters automatically reset and begin counting from zero. A separate set of RMON statistics is available for each MAC device in the IXF1104 MAC.

Implementation of the RMON Statistics block is similar to the functionality provided by existing Intel switch and router products. This implementation allows the IXF1104 MAC to provide all of the RMON Statistics group as defined by RFC2819. The IXF1104 MAC supports the RMON RFC2819 Group 1 statistics counters. Table 25 notes the differences and additional statistics registers supported by the IXF1104 MAC that are outside the scope of the RMON RFC2819 document.

Datasheet 80

Document Number: 278757

Revision Number: 009

Revision Date: 27-Oct-2005