Generic JTAG Device Support

Frozen Content

Modified by Admin on Sep 13, 2017

If a third party board contains a physical device that is not supported by the system, the device will appear in the Hard Devices chain of the Devices view (View » Devices View) as a Generic JTAG Device.

Figure 1. Generic JTAG
device detected in the Hard
Devices chain.

In this case no specific Nexus driver exists for the device (no .NEX file in the \System folder of the installation). To get the system to drive the Hard JTAG chain containing such a device, you will need to attach a Boundary Scan Description Language (BSDL) file for the specific device you are using. Such files can be obtained from the relevant Vendor website. Once attached, the system will use the information in the file – including the device's ID Code and Instruction Register Length – to correctly configure the Hard JTAG chain.

A BSDL file is attached to a Generic JTAG Device by right-clicking on the icon for the device, in the Hard Devices chain of the Devices view, and choosing the Configure JTAG ID Mapping command. The Generic JTAG Device dialog will appear (Figure 2).

Figure 2. Attaching a BSDL file to a generic JTAG device.

Simply click the Add button in the BSDL File Links region of the dialog – the entry enter BSDL filename will appear in the list. Either type the filename directly or click the folder icon at the right of the field to navigate to the required file. By default, the path is set to the \Library\BSDL\Generic folder of the installation. BSDL files should be placed in this folder.

By including the standard BSDL file supplied with each JTAG-compliant device, you have access to the pins on every JTAG device in your design, through the real-time JTAG Viewer panel. For more information, see Monitoring the State of Device Pins - Live.

The system can even handle the situation where a BSDL file is not available for a device. Simply set the correct instruction length for such a device (in the Generic JTAG Device dialog) and the JTAG system can continue to communicate to other devices in the chain. Without a BSDL file you will, however, not be able to interrogate the state of pins for the device using the JTAG Viewer panel.