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Documentation
CONTENTS

Speedgoat PCIe Interface

Speedgoat PCIe Interface — Used to read/write data from/to an FPGA register

Supported Modules

  • IO332-200k

  • IO333-325k, IO333-410k, IO333-325k-SFP, IO333-410k-SFP

  • IO334-325k, IO335-325k

  • IO342-1450k, IO342-1080k

  • IO397-50k

Interface

PCIe Interface

The PCIe Interface can be used to read/write data from/to an FPGA register with a width of up to 32 bits. Use vectorized ports to synchronize PCIe access of several registers.

  • PCIe-Read latency: 1.5 µs

  • PCIe-Write latency: 300 ns

  • Direction: input or output

Use Cases and Optimizations

PCIe Write

  • Synchronisation:If you would like to synchronize the write access of multiple registers so that the written values will be applied on the FPGA at the same time, implement the PCIe access as a vector of values. Data type conversion may be required as vectors are only allowed with the same data type. This concept ensures that there is no time difference compared to when a number of values are written to the FPGA.

  • Task Execution Time and Latency:Each PCIe access, whether it is a write or read access, takes time and can have an impact on the overall task execution time on the CPU. PCIe write accesses are only written if the values change compared to the previous sample step. If the PCIe registers are used as static configuration parameters, which must be written to the FPGA only once and are not altered during runtime, these parameters will only be written at the very first sample step and therefore do not impact the task execution time of the simulation run (note: the first task execution is treated exceptionally as it makes a longer execution possible compared to the consecutive sample steps). This concept is applied on single PCIe access as well as vectorized accesses.

PCIe Read (not implemented on the IO397 I/O modules)

  • PCIe Read Acceleration:The reading of register values from the FPGA can have a significant impact on the task execution time due to significant PCIe latency time. To accelerate the PCIe read time, a DMA PCIe access is used if the values are read in vectorized fashion and if the vector holds more than 3 values (with less than 3 values, the configuration of the DMA access takes more time than if treated as single PCIe accesses). The figure below illustrates the impact of PCIe register access on the task execution time of the DMA implementation compared to when the registers are read as single individual accesses. There is no further configuration needed for the DMA transfer, as all the settings are applied automatically if the requirements are met. Refer to the streaming DMA and DMA from the external DDR RAM for additional information on fast data transfer to and from the FPGA.

Interface Pin Mapping

There is no interface pin mapping.

Terminal Board

This interface does not require a terminal board.