Intel IXP400 manual CallBack, Polled

Intel® IXP400 Software

Access-Layer Components: HSS-Access (IxHssAcc) API

13.5.2.1CallBack

If the pointer to the rxCallback() is not NULL when ixHssAccChanConnect() is called, an ISR will call rxCallback() to handle Tx/Rx data. It is called when each of N channels receives bytesPerTStrigger bytes.

Usually, a Rx thread is created to handle the HSS channelized service. The thread will be waiting for a semaphore. When rxCallback() is called by IxHssAcc, rxCallback() will put the information from IxHssAcc into a structure, and send a semaphore to the thread. Then rxCallback() returns so that IxHssAcc can continue its own tasks. The Rx thread — after receiving the semaphore — will wake up, take the parameters passed by rxCallback(), and perform Rx data processing, Tx data preparation, and error handling.

For Rx data processing, rxCallback() provides the offset value rxOffset to indicate where data is just written into each circular buffer. rxOffset is shared for all the circular buffers in the pool. The client has to make sure the Rx data are processed or moved to somewhere else before overwritten by the NPE since the buffers are circular.

For TX data preparation, rxCallback() provides the offset value txOffset to indicate which pointer list in the pointer lists pool is pointing to the data buffers currently being or will be transmitted. As a result, the client can use txOffset to determine where new data needs to be put into the data buffer pool for transmission. For example, data can be prepared and moved into buffers pointed by the (txOffset-2)thpointer list.

rxCallback() also provides the number of errors NPE receives. The client can call function ixHssAccLastErrorRetrievalInitiate() to initiate the retrieval of the last HSS error.

13.5.2.2Polled

If the pointer to the rxCallback() is NULL when ixHssAccChanConnect() is called, it implies that the client will use a polling mechanism to detect when the Tx and Rx of channelized data is to occur. The client will use ixHssAccChanStatusQuery() to query whether channelized data has been received. If data has been received, IxHssAcc will return the details in the output parameters of ixHssAccChanStatusQuery.

ixHssAccChanStatusQuery() returns a flag dataRecvd that indicates whether the access component has any data for the client. If FALSE, the other output parameters will not have been written to. If it is TRUE, then rxOffset, txOffset, and numHssErrs — returned by ixHssAccChanStatusQuery() — are valid and can be used in the same way as in the callback function case above.

Figure 63 shows the Tx/Rx process.

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