Introduction

The FPGA Scope enables the monitoring of high-speed signals internal to an FPGA board connected to an OPAL-RT Simulator, acquired directly on FPGA at a rate faster than the simulation step. The feature relates to the low-level acquisition system, and when the feature is enabled, data is made available to the user for visualization through the ScopeView interface or through the DataLogger APIs.

Feature availability

The feature is available in all OPAL-RT firmware provided as an OPBIN file, for FPGA cards connected to the simulation through a PCI-express interface. It is enabled through the option “Enable FPGA Scope” in the OPAL-RT Board I/O configuration.

Typically, all simulator input/output signals are available for visualization through the FPGA Scope. Additionally, if present, FPGA-based controllers and solvers such as eHS, or custom probes on other functionalities, can provide signals to the FPGA Scope.

Selecting signals for acquisition

A list of signals available to the FPGA Scope feature is populated when the FPGA configuration file (bitstream) is created and embedded in the OPBIN file. Upon the selection of the OPBIN file as the “Bitstream configuration file” in the OPAL-RT Board configuration interface, the configuration file content is extracted in the “firmware” directory of the RT-LAB project.

In the folder corresponding to the firmware selected, the signals to acquire are selected through the <configuration_file_name>.fsd file.

In the file, signals are made available through different probes. Each probe groups signals from a specific source internal to the FPGA. The FSD file lists them in the JSON format, along with their numerical format. Signals are selected by the user by setting the “Selected” attribute to the value true. Additionally, adding the attribute “TriggerSelected” to the value true to a signal in the list will set it as the signal on which the trigger condition will be applied.

Only the attributes “Selected” and “TriggerSelected” should be modified by the user in the FSD file.

The maximum number of signals that can be selected simultaneously to be acquired is indicated as the “max_count_selected_signals” attribute at the top of the file. A maximum of one signal can have the “TriggerSelected” attribute set to true. If no signal has the “TriggerSelected” set to true or the signal that has “TriggerSelected” set to true is not selected, the first signal selected will be used for the trigger condition application.

Visualizing the signals

ScopeView

From the time the simulation is executed, the signals acquired by the FPGA Scope can be visualized in ScopeView following this procedure:

1. From RT-LAB, open ScopeView.
   
2. In ScopeView, load the Data Source by selecting the simulator IP address into the "Target" field of the DataLogger tab, then click "Fetch signal groups".
   
3. In "Signal Group" list, select "FPGAScope", then click "Load".
   
4. In the signal selection interface, select the signals to be visualized from the list of signals that were selected in the FSD file.
5. In the ScopeView oscilloscope interface, the trigger signal selection is displayed. Adjust acquisition period and window size, trigger characteristics and then run an acquisition by clicking the black "Start" button.
   

Example Model

The procedure above is illustrated in an example model for an OP4510 simulator. To try the example model, create a new project based on template Features > FPGAScope.

Additional information

Acquisition period

The minimal acquisition period depends on the number of signals selected for acquisition. As a rule of thumb, the minimal acquisition period in FPGA clock cycles is equal to the number of signals selected, plus one. This means that, considering a 200 MHz FPGA clock, the minimal acquisition period is 10 nanoseconds for one signal selected, 15 ns for two signals, 20 ns for three signals, etc.

One notable exception to that is that in some cases, more than one signal can be acquired simultaneously. As an example, all 32 signals coming from a digital input conditioning module are in general acquired simultaneously, and count for only one signal in the computation of the minimal acquisition period.

Acquisition window time length

The RAM memory that can be allocated to the data recovery is limited to 4 MB, limiting the maximum length of the acquisition window.

The maximum acquisition window length in seconds is inversely proportional to the number of signals selected for acquisition in the FSD file, and proportional to the acquisition period.

By default, when the FPGA Scope source is loaded in ScopeView, the window length is set to its maximum length for the signals selected and the default acquisition period. The window length must be manually shortened if the acquisition period is decreased. Window can be lengthened if the acquisition period is increased.