List of Figures

NXscope capture process

NXscope Generator GUI

file name

NXboard GUI

NXboard GUI scope menu

example 1 functional block diagram

example 2 functional block diagram

example 3 functional block diagram

display caused by an erroneous sample

NXscope Overview

NXscope is an embedded logic analyzer enabling you to record samples of your design’s internal signals at the rising clock edge and analyze the results in a waveform viewer.

• NXscope implements a NanoXplore IP Core generated by the NXcore Generator

• The capture process is controlled by JTAG through the ANGIE USB-JTAG adapter via NXbase2 software or the NXboard GUI

• The results are displayed and analyzed with either of the following tools:

  • The ModelSim Waveform Viewer, using a simplified testbench to read the TXT file generated by the NXcore generator

  • The GTKWave Waveform Viewer (free software)

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NXscope Capture Process

NXscope IP Core comprises 3 main functional blocks:

• The Trigger Engine
  A configurable module for detecting the trigger conditions to capture samples

• The Capture Unit
  A configurable module to store the captured samples

• The JTAG Interface
  Activates the trigger engine and transfers captured samples to the workstation through the ANGIE USB-JTAG adapter via NXbase2 software or the NXboard GUI

NXscope Features

Trigger Features

• 1 to 32 trigger input lines

• Optional trig_immediate input

• Single or dual sequential trigger conditions

• Level-based (basic) or level- and edges-based (basic_and_edges) triggers

Capture Settings

• Capture width: 2 to 240 input lines

• Capture depth: 2K, 4K, 6K, 8K, 12K, 24K or 48K

• Programmable number of samples stored before trigger condition

• Optional windowed capture mode (capture depth is sub-divided in multiple windows)

• Optionally stores the trigger pulse

• Optionally stores the Window number, if applicable

NXscope trigger conditions are flexible:

• Up to 32 trigger lines

• Single or two-level trigger conditions

• Basic trigger conditions on ‘0’, ‘1’ or ‘X’ on each one of the trigger lines

• Edge detection (rising, falling or both) on up to 32 trigger lines

• User’s defined pre-trigger storage (not available when two-level trigger is selected)

• Trig on condition(s)

• Trig immediate (no condition)

• Up to 240 sampled signals

Using NXscope is typically a 4-step process describes in the sections below.

Step 1: Generate the NXscope IP Core

The NXscope IP Core is generated using the NXcore Generator tool.

All triggers and data sampling parameters are defined by the user including:

• Number of data lines to be sampled (up to 240)

• Sampling depth

• Trigger conditions

Step 2: Instantiate the Generated NXscope IP Core in your Design

After generating your customized NXscope IP Core, you must instantiate it in your Design.

The Input and Output signals to be connected are as follows:

Inputs

Outputs

JTAG Pins

The captured samples are read by NXbase2 or NXboard software via the ANGIE USB-JTAG adapter.

Step 3: Implement the Design and Generate the Bitstream

1. Synthesise, Place and Route your design and generate your Bitstream using Impulse or nxpython as described in the Impulse Design Flow manual

2. Check the reports to ensure timing constraints are met

Step 4: Launch NXbase2/NXboard and NXscope Commands

Using NXbase2 software or the NXboard interface, follow these steps:

1. Load your Bitstream

2. Start the sample capture

3. Retrieve the captured data

See the NxBase2 User Manual for more detailed information about the available NXscope commands.

Once the data has been captured, an ASCII file is generated in TXT or VCD format.

You can review the TXT results via a simple testbench in the ModelSim waveform viewer or the VCD results using the free open-source GTKwave waveform viewing software.

Create a Custom NXscope IP Core

The NXscope Generator interface enables you to define all available parameters of the logic analyzer.

To launch the NXscope Generator, launch first the NXcore GUI (by typing the “NXcore” command at the prompt, and then, select the “NXscope” icon on the GUI left top side.

The next figure is a screen capture of the NXcore / NXscope Generator GUI. All customizable parameters are available on this single page.

Open

NXscope Generator GUI

When all NXscope parameters are set, the IP Core can be generated by pressing the « generate » command, in the bottom-right part of the window.

Entity Name

The NXscope Generator generates a VHDL encrypted file. The entity name is entered here. The VHDL path and file name are chosen with the “Generate” (bottom-right of the window).

The entity can then be instantiated in the design as a VHDL component.

The generated VHDL file includes a header (not encrypted) where the user can see the port names, modes, and width.

Capture Configuration Input line count: integer range 2 to 240

Up to 240 internal signals can be sampled and captured.

 Capture_depth: integer range 2048 to 49152

Defines the capture depth of the DATA_LINES sampled and stored on internal RAM block(s). The maximum depth is 48K.

Allowed capture depth (samples number):

• 2048 (2K)

• 4096 (4K)

• 6144 (6K)

• 8192 (8K)

• 12288 (12K)

• 24576 (24K)

• 49152 (48K)

Both “Capture_depth” and “Input line count” define the amount of internal RAM to be used by the IP Core, as:

• A single memory block can store up to 2048 x 24-bit words.

• With 10 RAM blocks up to 24K x 20-bit words can be stored.

 Capture_mode: “Pre-trigger” or “Multiple windows”

This setting enables you to assign one or more capture windows to the NXscope capture memory.

• “Pre-trigger”: the “Capture depth” is used as a single capture window that uses the whole depth. In this mode, the user can define the number of samples to be stored before reaching the trigger condition. For example, a 2048-word enables you store N samples before, and 2048-N samples after the trigger condition. Alternately, this mode supports a two-level trigger. In this case, a first trigger condition must be met, then the second (and final) trigger condition starts the data capture.

• “Multiple windows”: the “Capture depth” is divided into multiple sub-windows allowing multiple captures until filling the complete available RAM. As an example, if “Capture depth” = 2K, the user can define 4 windows of 512 samples. The setting of “Window capture length” defines the length of the sub-windows.

 Window capture length: integer range 64 to 2048

This setting enables you to define  the length of the  capture  windows when  “Capture mode” = “Multiple windows”.

 Pre-trigger_samples: integer range 0 to capture_depth-1

• When “Capture mode” is set to “Pre-trigger” and “Multiple level trigger” is “false” it’s possible to sample data before reaching the trigger condition. “Pre-trigger samples” defines the number of samples acquired before the trigger condition is met.

• If “Multiple level trigger” is set to true, the value of “Pre-trigger samples” is ignored, and the capture starts when the second trigger condition is met.

However, in any mode, the user has still the option to store up to 2 samples to be acquired before triggering, by using the “User data delay” setting.

 User data delay: integer range 0 to 2

Available in all trigger modes, this setting allows to storage of 0 to 2 samples before meeting the trigger condition. It can be particularly useful in “Multiple windows” mode, or “Pre-trigger” if “Multiple level trigger” is set to true. It allows to capture and visualize up to 2 samples before the trigger condition is met.

Note that this option requires using additional logic resources for implementation.

 Store trigger pulse: Enable or Disable

This setting enables you to store the trigger pulse (when the trigger condition is met), so it can appear automatically as an additionally captured data_line.

When “Store trigger pulse” = “Enable”, the number of sampled signals is then:

        Input line count + 1

The user’s defined sampled bits being Input line count -1 downto 0, so the weight (index) of the trigger pulse in the captured flow is “Input line count”.

 Store window number: Enable or Disable

When “Capture mode” is set to “Multiple windows”, the total capture depth is split into several capture windows. The length of each window is defined with the “Window capture length” parameter.

NXscope gives the user the ability to store the window number for each partial capture. This option can be helpful for the visualization and identification of several capture sets.

When “Store window number” is set to “Enable”, four additional bits are stored in the capture memory, giving up to 16 different window numbers (can be helpful to identify each capture window when displaying the resulting waveform. The number of signals sampled by NXscope will be:

o   “Input line count” + 4 if “Store trigger pulse” = “Enable”. In this case, the windows number are stored as:

(“Input line count” + 3 downto “Input line count”).

o   “Input line count” + 5 if “Store trigger pulse” = 1”. In this case, the window number are stored as:

(“Input line count” + 4 downto “Input line count” + 1).

Trigger Configuration

Trigger line count: integer range 1 to 32

Trigger mode: “Basic” or “Basic & Edges”

There are 2 trigger modes:

Multiple level trigger: “Enable” or “Disable”

When “Capture mode” is set to “Pre-trigger” the user can define a two-level trigger condition. The analyzer will search first for the first level trigger condition, before searching for the second level and final trigger condition and start the data capture. For this, the “Multiple level trigger” must be set to true, and the “First level trigger value” must be defined by the user.

The NXscope IP Core output goes from a low state to high when the first trigger condition has been met. 

Trigger Value

When “Trigger mode” is set to “Basic”, each trigger line will be compared to the following possible values: ‘0’, ‘1’ or ‘Ignore’

When “Trigger mode” is set to “Basic & Edges”, each trigger line will be compared to the following possible values: ‘0’, ‘1’, ‘Rising edge’, Falling Edge’, ‘Both Edges’ or ‘Ignore’

First level trigger value:

When” Multiple level trigger” is set to “Enable”, the pre-trigger condition must be specified too.

If this option is disabled, the “First level trigger value” is ignored.

NXscope IP Core Generation:

Once the NXscope parameters are set, press the “Generate” command icon in the bottom-right part of the window.

A new window appears. It allows you to choose both file name and path.

A VHDL encrypted file is then generated. A header in clear VHDL (not encrypted) is available. This header appears as comments. It can be used for the component declaration when instantiating the NXscope IP Core in the design to be analyzed.

NXscope Capture Tools

After compiling the design, the user must send the bitstream to the FPGA and then launch the data capture.

You can launch the capture using NXbase2 or NXboard as described in the sections below.

Launch Sample Capture with NXbase2

Use NXbase2_cli to run the following commands:

1. Load the bitstream:

   >> NXbase2_cli –s /bitstream_path/bitstream_name.nxb

2. Launch a capture*:

   • For a (ModelSIM) TXT file

     >> NXscope capture dump.txt 50E6

   • For (GTKWave) VCD file

     >> NXscope capture dump.vcd 50E6

*Where 50E6 is the frequency of the sample clock for the design (50 * 10**6 = 50 MHz in this case).

The frequency value does not impact the acquisition. It is used to generate the VCD file if this format is chosen. 

Launch Sample Capture with NXboard

At the prompt, launch the following command:

NXboard GUI appears:

By selecting the “Bitstream” icon (on the left side of the GUI), the user can browse through the folders and choose the bitstream to be sent to the FPGA.

Note that if the FPGA is already configured, it must be reset by the JTAG chain before being re-configured with a new bitstream.

After the FPGA has been loaded with the bitstream containing the NXscope, select the “Scope” icon (left side of the GUI) to enter the capture command.

The path and file name can be chosen. Press the “Capture” icon to arm the trigger and launch the capture.

Note that the value given to the “Capture Frequency” is taken into account only for the VCD file generation if this format is chosen.

A message will be issued after the captured data has been stored in the specified file.

NXscope results format:

NXscope can store the captured results in two possible formats:

• .txt: preferred format for waveform display on ModelSim/QuestaSim

• .vcd: preferred format for waveform display on GTKwave – free software

NXscope Capture Sequence

After configuring the FPGA with the bitstream containing the NXscope IP Core and before launching the NXscope capture command, the “DONE” and ‘TRIG_ARMED” output pins of the NXscope IP Core are low. The IP Core is waiting for a command.

When launching the capture, the “TRIG_ARMED” goes high. The NXscope IP Core is waiting for the trigger condition(s).

When the trigger condition is found, the capture starts, the “TRIG_ARMED” output pin goes low, and the data capture starts.

After filling the assigned internal RAM the capture stops and the “DONE” output goes high. At this time, the NXboard / NXbase2 software starts reading the captured data via the ANGIE USB-JTAG adapter. A message appears on the console to inform that reading is complete.

A new capture can then be started if required.

To prevent such a situation, it’s possible to use the optional input pin of the NXscope IP Core “TRIGGER_IMMEDIATE”. This pin must be tied to a low state in a normal situation. When it goes high, an immediate acquisition is started, ignoring the trigger condition(s).

NXscope capture and display example

Launch NXbase2/NXboard and NXscope commands

To sample the data lines, you must use the Angie USB-JTAG adapter, and the NXbase2 software or NXboard GUI.

The bitstream must first be loaded before the capture can be launched as specified in the previous section.

For detailed information about the available commands please refer to the NxBase2 user’s manual.

Once the data has been captured, an ACSII file is generated (.TXT or .VCD). The results can be then analyzed in the ModelSim waveform viewer (.TXT result file), with a simple testbench or with the free GTKWave waveform display software using the .VCD result file.

Display and analysis of the captured results

Open ModelSim and launch the testbench simulation

As mentioned previously the ModelSim waveform viewer can be used to visualize and analyze the captured results (.TXT result file).

The. TXT file generated with the sampled results is read by a simple testbench, to be converted to graphic waveforms.

See the following example:

The user can then set its own waveform settings.

Open the .VCD result file with GTKWave and view/analyze the captured results

GTKWave is a free waveform display software. It enables you to display the waveform of signals that are stored in .VCD format.

Please, refer to the GTKWave documentation for detailed information.

NXscope IP Core configuration examples

The following shows three different examples of NXscope configurations.

Example 1: 12K x (25 + 1) capture with 50 samples pre-trigger condition

Number_of_trig_lines = 4

Input line count = 25

Capture depth = 12K

Capture mode = Pre-trigger

Pre-trigger samples = 50

User data delay = 0

Store trigger pulse = Enable

Trigger line count = 4

Trigger mode = Basic

Multiple level trigger = Disable

Trigger value = 1, 0, Ignore, 1

Functional block diagram

Example 2: 24K x (33 + 1) capture (2 samples pre-trig cond)

Number_of_trig_lines = 6

Input line count = 33

Capture depth = 24K

Capture mode = Pre-trigger

User data delay = 2

Store trigger pulse = Enable

Trigger line count = 6

Trigger mode = Basic & Edges

Multiple level trigger = Enable

Trigger value = 0, X, 1, R, 1, 1

First level trigger value = F, 1, 0, X, 1, R,

Functional block diagram

5.3    Example 3: 8K x (42 + 1 + 4) capture (2 samples pre-trig cond)

Number_of_trig_lines = 8

Input line count = 42

Capture depth = 8K

Capture mode = Multiple windows

Window capture length = 1024

User data delay = 2

Store trigger pulse = Enable

Store window number = Enable

Trigger line count = 8

Trigger mode = Basic

Trigger value = 0, 1, 1, X, 1, 0, X, 1

Functional block diagram

6 Known issues

Erroneous single sample in the captured stream:

Depending on NXscope settings, a dummy sample can be inserted into the captured stream.

This sample can appear anywhere in the waveform. Fortunately, it’s easy to recognize, and it must be ignored.

This “fake” or “pseudo” sample always exhibits all bits to ‘0’. It must be ignored.

The following figure shows an example of the display artifact caused by this erroneous sample in the captured stream.

NanoXplore is working to correct this problem as soon as possible.

7 How to order a NXscope license

NXscope license is not included in the “nxmap” software. A separate license must be ordered.

Please contact sales@nanoxplore.com