Panavia receiver channels have a Last Value Table, a small receive ring buffer, an Acquisition FIFO and a set of filters and a loopback data structure.

Each of the 32 possible Panavia tags has an entry in the Last Value Table. As the name suggests, the LVT contains the last value that has been received for each Panavia Tag. The hardware can be set to generate an interrupt when a new value is being entered into the LVT.

Each Tag also has a small ring buffer. This buffer contains (at most) the last ‘n’ values received for the Tag, where ‘n’ is the size of the ring buffer. Functions within the library allow the programmer to determine how many Tags are in the ring buffer, and to extract one, several or all of them. Indication of a buffer overflow condition is also given.

The Ring Buffer is intended to relieve the host PC of the ‘Interrupt overload’ that can be caused by setting the hardware to generate an interrupt when the LVT is updated. Using the ring buffer allows the user to polling the Tag of interest to determine if, and how many, new tags have been received at a much slower rate than would be required to provide the same functionality using the LVT.

The LVT and Ring Buffer may be a dual-port-memory on some cards (as on the ATT RT16 card), or it could be held in system memory (as on the ATT PCMCIA cards). No-matter what the hardware, common functions are used to access the LVT and Ring Buffer, which allows hardware independent application software to be written.

The Filters and Acquisition FIFO work together to allow all or selected bus traffic to be stored in chronological order, typically for later analysis. Each Tag has its own filter word. A bit in the filter word determines if that Tag is to be stored in the Acquisition FIFO. An optional interrupt can be generated once the FIFO becomes half full. The PC can then read the data from the FIFO as a block of data, and for instance, save the block to disk. In addition to filtering for acquisition, a bit can be set to start acquisition once a certain Tag has occurred. This type of filter is called a Trigger filter.
The Acquisition FIFO may be a real hardware FIFO on some cards (as on the ATT RT16 card), or it could be held in system memory (as on the ATT PCMCIA cards). No-matter what the hardware, common functions are used to access the LVT and FIFO, which allows hardware independent application software to be written.

To support data ‘loopback’, each Tag has its own loopback data structure. This structure allows the programmer to specify two modes of operation where data received on a receiver can be re-transmitted by a Panavia transmitter.

The first mode allows the user to specify a transmitter channel on which the Tag will be re-transmitted. This loopback tag will be placed into the loopback buffer of the specified transmitter, which will then transmit the Tag during the next available gap in its scheduled transmitter (polling) list.

The second mode allows the programmer to specify a transmitter channel transmit lookup table entry that will be updated when the Tag is received. This permits the data being transmitted by the transmitter polling list to be updated with data that is being received on the receiver.

All the functions of a Panavia Receiver channel described above can be run independently, or concurrently.

For a turn-key solution to many applications, a menu driven software package running under Microsoft Windows is available, see http://gssprojects.com.

For users wishing to write their own software, an Application Program Interface (API) complete with source code is available. Written in Microsoft C, this code can be compiled into a library suitable for both Windows and DOS based applications. It can also be compiled into a self contained Windows DLL.