7 Adv Host Integration 1234869680124198 3


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7 Adv Host Integration 1234869680124198 3

  1. 1. Lesson 7 Synchronizing FPGA and Host Data Transfers TOPICS A. LabVIEW FPGA and Host Communication B. Synchronization C. Direct Memory Access (DMA) FIFOs D. Lossless Data Transfer E. Interrupts F. Handshaking ni.com/training
  2. 2. A. LabVIEW FPGA and Host Communication • FPGA VI and host VI are inherently asynchronous • Each VI runs independent of the other • Data transfer synchronization needs to be implemented based on the application needs • To transfer large amounts of data between the target and host at high rates you must buffer the data ni.com/training
  3. 3. Synchronization and Buffering • Synchronization—Causing tasks occur at the same time or in unison by using clock, triggers, or events • Buffer—An area of computer memory that stores multiple data items ni.com/training
  4. 4. B. Synchronization • Level of synchronization depends on the application • Synchronization not required in some slower control applications − For example, if the data acquisition loop is faster than the control loop, the control loop reads the most recent value • Synchronization required to acquire and transfer lossless data at a known rate ni.com/training
  5. 5. Asynchronous vs. Synchronous • Asynchronous Applications − Applications that don’t require tight synchronization for control or data processing − Timing performed on the FPGA, but no synchronization to the host application − Most recent data is okay, many control applications • Synchronous Applications − Synchronization required between FPGA VI and host VI ni.com/training
  6. 6. Synchronous Applications • Timing control − Timing from the FPGA/acquisition controls the timing/loop rate of the host VI, and vice-versa • Synchronized Data Transfer − Synchronization transfers/streams data from acquisition to host VI for processing and logging − Lossless data transfer ni.com/training
  7. 7. Synchronization Methods • Direct Memory Access (FIFO) • Interrupts • Handshaking ni.com/training
  8. 8. C. Direct Memory Access (DMA) FIFOs Data Buffering • To transfer larger amounts of data at high rates between the target and the host you must buffer your data. • The best way to buffer data is by using Direct Memory Access (DMA) data transfer methods. ni.com/training
  9. 9. Direct Memory Access (DMA) FIFOs (continued) • Transfers data from FPGA directly to memory on the RT controller through bus mastering. • Streams large amounts of data. • Provides better performance than using local FIFO and reading indicators. • Host processes data while FPGA transfers data to host memory. • Without DMA, processor must read data. • Consists of two parts—FIFO part and host part. • FPGA writes data one element at a time to the FPGA memory. • DMA engine transfers data along PCI bus to host memory. ni.com/training
  10. 10. Demonstration: Target-to-Host DMA FIFO Explore how the FPGA transfers data to the host. GOAL <Exercises>LabVIEW FPGADemonstrations ni.com/training
  11. 11. Demonstration: Host-to-Target DMA FIFO Explore how the host transfers data to the FPGA. GOAL <Exercises>LabVIEW FPGADemonstrations ni.com/training
  12. 12. Creating DMA FIFOs • Create DMA FIFO the same way as FPGA FIFOs − Right-click target − Select New»FIFO − Choose Target to Host or Host to Target as Type • All DMA FIFOs are U32 data type − Must convert to and from U32. ni.com/training
  13. 13. Writing Data to a Target-to-Host DMA FIFO Drag FIFO from Project Explorer window. ni.com/training
  14. 14. Writing Data to a Target-to-Host DMA FIFO (continued) FIFO Write Function • Element—Inputs the data element to be stored. • Timeout—Inputs the number of clock ticks the function waits for available space in the FIFO if the FIFO is full. The default is 0, or no wait. A value of –1 prevents the function from timing out. • Timed Out?—Returns True if space in the FIFO is not available before the function completes execution. − If Timed Out? is True, the function does not add Element to the FIFO. ni.com/training
  15. 15. Reading Data from a Target-to-Host DMA FIFO Read a DMA FIFO in the host: 1. Open a reference to the FPGA 2. Add an Invoke Method function 3. Choose the DMA FIFO»Read method ni.com/training
  16. 16. Reading Data from a Target-to-Host DMA FIFO (continued) Read a DMA FIFO on the host: • Number of Elements − Function completes when elements are read or timeout is reached − Same overhead regardless of the number of elements; read more elements if host is too slow • Timeout—Time to wait before timeout (–1 = indefinite wait; Default is 5,000 ms) ni.com/training
  17. 17. DMA FIFO with Blocking Implementing a DMA FIFO with blocking: • User specifies number of elements • Best method when input/output rate is known ni.com/training
  18. 18. DMA FIFO with Polling Implementing a DMA FIFO with polling: • Acquires as many samples as are currently available • Best when the input/output rate is unknown ni.com/training
  19. 19. Writing Multiple Channels Writing multiple channels of data to a DMA FIFO by interleaving ni.com/training
  20. 20. Reading Multiple Channels Reading multiple channels from a DMA FIFO in the host ni.com/training
  21. 21. D. Lossless Data Transfer • Lossless Application • Overflow—DMA Full? • Underflow—Check for –50400 ni.com/training
  22. 22. Overflow Overflow—too many data points for buffer, may lose data • Acquire data slower • Increase number of elements to read on the host • Increase the rate that the host reads data • Increase buffer sizes on FPGA and host ni.com/training
  23. 23. Demonstration: Target to Host DMA FIFO – Overflow Explore how overflow of the DMA FIFO occurs if the RT host VI is too complex. GOAL <Exercises>LabVIEW FPGADemonstrations ni.com/training
  24. 24. Underflow Underflow—not enough data to read, FIFO read times out • Increase timeout • Read data less often • Read smaller sets of elements • ni.com/training
  25. 25. Demonstration: Target to Host DMA FIFO – Underflow Explore how underflow occurs when the DMA FIFO tries to read data before it is available. GOAL <Exercises>LabVIEW FPGADemonstrations ni.com/training
  26. 26. Exercise 7-1: DMA-Based Data Transfers Observe how DMA-based handshaking works. GOAL ni.com/training
  27. 27. E. Interrupts • Send a trigger from the target to the host application. • Why use an interrupt? − Eliminate polling − Allow host to perform other operations while waiting for the Interrupt signal • Communicate over a physical hardware line ni.com/training
  28. 28. Advantages of Interrupts • An interrupt requires execution of a low-level driver on the host, so a host can process more polling operations/s than interrupts/s • Comparison statistics for a Networked RIO Device: − A single poll requires 10 s − An interrupt requires about 250 s • Use Interrupts when FPGA sends data less often and host must do other processing ni.com/training
  29. 29. Implementing an Interrupt ni.com/training
  30. 30. Implementing an Interrupt (continued) Interrupt Express VI • IRQ Number − Specifies which logical interrupt (0 – 31) to assert − Default is 0 • Wait Until Cleared − Specifies if this VI waits until the host VI acknowledges the logical interrupt − Default is False • Wait Until Cleared as True causes jitter due to dependency upon the host VI ni.com/training
  31. 31. Host and Interrupts • Host must acknowledge interrupts • Use Wait on IRQ and Acknowledge IRQ methods − IRQ Number(s)—specifies the logical interrupt or array of logical interrupts for which the function waits − Timeout (ms)—specifies the number of milliseconds the VI waits before timing out. –1 = infinite timeout − Timed Out—returns TRUE if this method has timed out − IRQ(s) Asserted—returns the asserted interrupts. Empty or –1 array indicates that no interrupts were received ni.com/training
  32. 32. Acknowledge IRQ Method • Acknowledges and resets to the default value any interrupts that occur − Wire after the Wait on IRQ method − IRQ Number(s) specifies the logical interrupt or array of logical interrupts for which the function waits ni.com/training
  33. 33. Interrupt Example ni.com/training
  34. 34. DMA FIFO with Interrupts Implementing a DMA FIFO with an interrupt • Prevents the CPU from polling the DMA FIFO to see if elements have arrived − Least resource intensive DMA FIFO transfer method − Slowest DMA FIFO transfer method due to IRQ delay ni.com/training
  35. 35. Exercise 7-2: Interrupt-Based Handshaking Observe an example of how interrupt-based handshaking works. GOAL ni.com/training
  36. 36. F. Handshaking Handshaking—Checks that a receiving device is ready to receive or a transmitting device is ready to transmit • Handshaked synchronization—occurs when two or more devices act in sequence • Host uses Boolean controls and indicators (data available and data read flags) on the target to coordinate operations • Requires polling • Assures that all data that is sent is also received ni.com/training
  37. 37. Handshaking Process 1. FPGA acquires data and writes values to Array 2. FPGA writes True to Data Available 3. When Data Available is True, host reads data 4. After reading data, host writes True to Data Read 5. FPGA loop iterates when Data Read is True ni.com/training
  38. 38. Quiz 1. Which of the following are 2. What error are you likely methods of transferring to get if you create a DMA data from the target to the FIFO that is too small? host? a. Underflow a. Handshaking b. Overflow b. Target-scoped FIFO c. Evenflow c. Interrupt d. DMA FIFO e. FTP ni.com/training
  39. 39. Quiz 3. What happens when a 4. Which technique requires DMA FIFO has an the host VI to use polling? underflow condition? a. Handshaking a. The FPGA resets b. Interrupts b. The FIFO Read throws c. DMA FIFO Error –50400 c. The Timed Out? indicator latches true ni.com/training