Using Probes

Probes are pins that are added to monitor specific signals in the hardware without reimplementing a design. Use the Probes command to add, save, and restore probes in your design. Probes are used to examine the signal states of the targeted FPGA device.

Adding a Probe

Select Tools > Probes to display the Probes dialog box.
Select the Add option to display the Define Probe dialog box.
Fill in the dialog box to define the probe.

Note You can select probe pins automatically or manually in the Select Pin Numbers section of the Define Probe dialog box. The Manual option enables the additional options in this section to allow you to specify the pin numbers for the routed probe. The Automatic option disables the additional options.

Select OK to close the dialog box. The probe is automatically routed, and the defined probe is displayed in the Probes dialog box.

Note You can optionally highlight probe(s) by selecting one or more rows in the Probes dialog then selecting a color from the drop-down list and clicking the hilite button.

Select the Bitgen option in the Probes dialog box to display the Run BitGen dialog box.
The file name displayed in the Bit File Name field is the name of your probed design. If you change the name to design_name.bit, you are warned that this name represents your unprobed design. You can select Yes to save the bit file under this name or No to save the bit file under the name provided by the system.
Click OK to return to the Probes dialog box.
Select the Download option to start the iMPACT tool so you can download your bit file to a test device. This tool is run in a separate process from the FPGA Editor.

Adding Probes without Routing

1. Use the following command:

probe add <netName> -targetPins <pinName1> [<pinName2>...] -noroute

2. To route the probes use the following command:

probe route -all

Saving a probe

Select Save Probes in the Probes dialog box to display the Save As dialog box. Enter a file name in the File Name field. Your probe definition including optional highlighting is saved as a script file with a .scr extension (probes.scr is the default file name).

Opening a probe script file

Select Open Probes in the Probes dialog box to display the Open dialog box. Select the probe script file containing the commands that define the probe. When the script is opened, the commands are performed, and the probe definition is added to the probes list.

Typical Use Case

The following is a common example about using probes.

Make a copy of your routed NCD design to be used for probe insertion.

Note Probes should only be copied on a temporary copied NCD, which should never be used for back annotation.

Load the copy NCD and PCF file into FPGA Editor.

Use the FPGA Editor Probe Tool for the following Tasks:

- Creating Probes for the appropriate networks.
- Generating the bit stream with the present of probes.
- Download the bit stream onto your device for testing.

Use iMPACT to observe the state of the electrical signal of the associated chip pins of the probes. Keep track of modifications and manually reproduce it to your original circuit because modifications can not be back annotated into your design.

Before exiting FPGA Editor, follow the prompts to save the probes into a script file. This script can be used to recreate the probes, assuming the net names have not changed between sessions.

Do not create the bit stream from the copy NCD that was created for probing. If used, the probes will exist in your final design and may have adverse affects on your timing.