Literature-Serial FPDP White Paper
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“SERIAL FPDP – MORE THAN AN EXTENSION OF FPDP” Curtiss-Wright Controls Embedded Computing Data Communications 4126 Linden Ave. Dayton, OH 45432-3068 USA Phone: 937-252-5601 or FAX: 937-258-2729 E-mail: [email protected] or WWW: www.cwcembedded.com ABSTRACT The Front Panel Data Port (FPDP) provides a high- Serial Serial FPDP FPDP speed connection between the A/D converter of a front- OUT IN end data generating system (such as a radar antenna) and Data Data Source FPDP FPDP IN IN Destination the digital signal processors (DSP) that are used to proc- With With FPDP OUT ess the incoming data stream in real time. Data FPDP IN Flow Control Parallel Parallel However, FPDP has a major limitation – the front-end FPDP FPDP Connection Connection data generation system must be located within one to five meters of FPDP cable length (depending on the 10 kilometer max FPDP configuration) of the DSP system. This presents a problem in many real world applications, that require Figure 1—Serial FPDP Concept greater distance between sensor and processor. Land- based radar systems, for example, may require that the EXPANDING SERIAL FPDP A/D subsystem be located as close as possible to the Serial FPDP has moved beyond this initial process flow antenna, and the processor system be located in an area and has become more than an extension of FPDP. It pro- quite distant from the antenna. vides solutions for many types of real time data stream- ing scenarios – many of which are not FPDP applica- Serial FPDP (VITA 17.1), the technology pioneered in tions. Serial FPDP has evolved into a “general-purpose” our FibreXtreme products, was developed to overcome high performance data link, providing high speed, bi- this distance limitation. It presents a straightforward directional data flow (with flow control) across multiple approach to serializing the FPDP data stream and trans- platforms. It supports both point-to-point and broadcast mitting it over extended distances. This paper outlines topologies. It also has the flexibility to support other the concept of Serial FPDP, provides solutions for sev- buses (PCI, RACEway) and has been implemented eral types of real-time data scenarios, and explains sup- across multiple form factors (PCI, PMC, VME). Soft- ported topologies. ware communications drivers have been developed for a variety of operating systems. Figure 3 expands the initial INTRODUCTION Serial FPDP concept and provides a more representative Serial FPDP extends the maximum distance of FPDP view of this expanded Serial FPDP process flow. connections by serializing the FPDP data stream and transmitting it over extended distance using copper or fiber optic cable. On the transmit side, the parallel FPDP FPDP In FIFO Encode Serialize Transmit data is converted to Serial FPDP. On the receive side, Data the reverse is true – the Serial FPDP data is converted back into the FPDP parallel data stream. The basic Receive Deserialize Decode FIFO FPDP Out FPDP-to-Serial FPDP transaction process is also Figure 1 – FPDP to Serial FPDP Initial Process Flow straightforward. The 32-bit FPDP input data passes Figure 2—FPDP to Serial FPDP Initial Process Flow through the transmit FIFO to the 8B/10B Encoder. The encoded data is then inserted into a continuous stream of SERIAL FPDP PROTOCOL idle characters being sent by the serializer, and the seri- In addition to transferring FPDP standard 32-bit data alized stream is transmitted across the media (either fi- words, Serial FPDP also transmits the control signals ber or copper) by the transceiver. Figure 1 illustrates this used by FPDP. These signals are encoded as part of a concept. series of special characters that are used to frame the data for transmission across the link. Three FPDP sig- On the receive end, the data is deserialized, decoded, nals (DIR, DVALID, SYNC) are set by the FPDP (and and placed in the receive FIFO for sending via the stan- Serial FPDP) transmit operation and two FPDP signals dard FPDP connection. Figure 2 illustrates this concept. (NRDY, SUSPEND) are set by the receive operation. There are eighteen ordered sets used by Serial FPDP to FPDP denote different information. Eight start-of-frame (SOF) or FIFO Encode Serialize Transmit PCI sets are used to embed three bits at the start of a frame. or The SOF ordered sets embed three FPDP signals – Raceway FIFO Encode Deserialize Receive or PIO1, PIO2, and DIR. Four status end-of- frame ??? (SEOF) sets are used to embed two bits at the end of the Data and Flow frame. The four EOF ordered sets embed the FPDP sig- Control Data and Flow Control nals NRDY and Overflow. FPDP Receive Deserialize Decode FIFO or There are two additional EOF ordered sets used by Se- PCI or rial FPDP to denote the actual end-of-frame. The Mark Transmit Serialize Encode FIFO Raceway EOF (MEOF) denotes a frame that has SYNC associated or ??? with it, and the Frame EOF (FEOF) denotes a normal data frame. The other four ordered sets are inter-frame padding used to denote flow control informa tion and alternate frame interpretations. Figure 3—Expanded Serial FPDP Processing Flow Serial FPDP uses a series of frames to structure the data Two other FPDP signals (PIO1 and PIO2) are user de- flow. These ordered set are used as part of this framing finable and are available to be set/read from either side structure. of the link. Figure 4 shows the FPDP control signal flow across the Serial FPDP link. These signals are accessed Serial FPDP has three basic frame types - a data frame, a directly from the input source when that source is actu- SYNC without data frame, and a SYNC with data frame. ally FPDP. They are typically accessed from a special The data per frame is variable, with a maximum size of register that is updated either by custom hardware or the the data buffer in a single frame of 512, 32-bit words software driver in non FPDP applications. (2048 bytes). SYNC is used to delimit data streams and maintain host program synchronization. Whenever a Serial FPDP protocol uses the Fibre Channel link layer protocol to actually transmit the data. The standard Fibre Normal Data Frame Channel link layer protocol defines certain data sets in (Sent Empty when no data is available) the 8B/10B encoding scheme as ordered sets. These or- Payload GO/ IDLE SOF Between 0 and 512 CRC FEOF SEOF STOP dered sets denote special control information for Fibre 32-bit words of data Channel. Serial FPDP uses a subset of these same or- dered sets, but assigns them a different meaning. Using the same 8B/10B encoding as Fibre Channel allows the Sync without Data Frame same components (ENDEC, SERDES) developed for Payload GO/ IDLE SOF Between 0 and 512 CRC FEOF SEOF STOP Fibre Channel to be used to implement the Serial FPDP 32-bit words of data link layer. Sync with Data Frame Payload GO/ SWDV SOF Between 0 and 512 CRC FEOF SEOF STOP 32-bit words of data ORDERED SETS IDLE:An ordered set used to pad a DATA or SYNC without DATA Frame. SWDV:An ordered set used to pad a SYNC with DATA Frame. SOF:An ordered set used to pad and to indicate the start of data in frame. It carries the state of three signals PIO1, PIO2, and DIR. OPTIONAL DATA (not an ordered set) CRC:If disabled, CRC is not present. If enabled and there is data in the frame, CRC is valid and checked. If enabled and there is no data in the frame, CRC is invalid and ignored. TYPE OF FRAME FEOF:DATA Frame. MEOF:SYNC Frame. SEOF:Carries the state of two signals, NRDY and transmit overflow. FLOW CONTROL FOR RETURN LINE STOP:Suspend. GO:OK to transmit. Figure 1 - Serial FPDP Framing Protocol with Figure 4—FPDP Control Signal Flow Figure 5—Serial FPDP Framing Protocol with Ordered Sets SYNC is recognized, the current frame is terminated and Extending Serial FPDP into a more general I/O solution the proper SYNC frame (SYNC w/data or SYNC w/o requires providing support for many common processing data) is sent. Figure 5 shows the three types of frames platforms – typically PCI bus-based systems. These sys- and the ordered set placement within those frames. tems require I/O interface products in various form fac- tors – including PCI, PMC and CPCI. Additionally, the I/O is controlled by and must interface with a variety of COMMUNICATIONS LINK EFFICIENCY Real time data streaming applications demand an effec- operating systems, each with its own intricacies. The tive communications scheme – one that efficiently util- actual performance, as measured by sustained data izes the bandwidth of the link to move data, not to proc- throughput, is dependent on many variables – including ess overhead structure. Serial FPDP’s point-to-point the specific PCI system design (processors, memory architecture meets this requirement by eliminating any speeds, etc.); the I/O handling efficiency of the different overhead associated with arbitration and node address- operating systems; the design of the driver software for ing. The very minimal set of status and control signals these operating systems; and the user’s application soft- (based on FPDP) eliminate the need for elaborate frame ware. Due to these many variables, there is no direct headers. method to calculate the efficiency of these common processing systems. Testing has proven to be the only A Serial FPDP data frame consists of either five or six method to determine the actual throughput rates. 32-bit data words (five without CRC and six with CRC).