Intel IXP400 manual Receive Triggers Rx-Free-Low Notification, Receive Processing

Intel® IXP400 Software

Access-Layer Components: ATM Driver Access (IxAtmdAcc) API

In order to receive a PDU, the client layer must allocate IXP_BUFs and pass their ownership to the IxAtmdAcc component. This process is known as replenishment. Such buffers are filled out with cell payload. Complete PDUs are passed to the client. In the case of AAL 5, an indication about the validity of the PDU — and the validity of the AAL-5 CRC — is passed to the client.

In the case of AAL 0, PDU completion occurs either when an IXP_BUF is filled, or is controlled by a timer expiration. The client is able to determine this by the fact that the IXP_BUF will not be completely filled, in the case that completion was due to a timer expiring.

Refer to the API for details about the AAL-0 timer.

IxAtmdAcc supports prioritization of inbound traffic queuing by providing two separate receive streams. The algorithms and tuning required to service these streams can be different, so management of latency and other priority constraints, on receive VCs, is allowed. As an example, one stream can be used for critical-time traffic (such as voice) and the other stream for data traffic.

The streams can be serviced in two ways:

•Setting a threshold level (when there is data available)

•Polling mechanism

Both mechanisms pass buffers to the client through a callback. Once the client is finished processing the buffer, it can either ask to replenish the channel with available buffers or free the buffer back directly to the operating-system pool.

4.5.3.1Receive Triggers (Rx-Free-Low Notification)

IxAtmdAcc receive service does provide a Rx-free-low notification service that can be configured to execute a client supplied notification callback when the number of available buffers reaches a certain low level. The service is supported on a per-VC basis and the maximum threshold level is

16 unchained IXP_BUFs.

4.5.3.2Receive Processing

When buffers have been received on a port, they are placed in one of two Rx streams common to the VCs sharing this resource as decided by the client when establishing a connection. IxAtmdAcc does not autonomously process this stream, but instead the client decides when and how many buffers will be processed.

Processing primarily involves handing back ownership of buffers to clients. The rate at which this is done must be sufficient to ensure that client requirements in terms of latency are met. The details of the exact rate at which this must be done is implementation-dependent and not within the scope of this document.

Receive — Based on a Threshold Level

IxAtmdAcc provides a notification service where a client can choose to be notified when incoming PDUs are ready in a receive stream as shown in Figure 19.

April 2005	IXP400 Software Version 2.0	Programmer’s Guide
64	Document Number: 252539, Revision: 007