The default communication path from the DPC in the Versal PMC to the AXI4 Debug Hub is the PMC-to-NoC interface. It is also possible to use other PS interfaces for this connectivity. In rare circumstances where these AXI-based interfaces from the PS or PMC cannot be used (for example, AXI timeout), it may be necessary to use a different communication pathway for debug core connectivity.
The BSCAN Fallback feature enables connectivity between the DPC in the Versal PMC and the AXI4 Debug Hub without using AXI. This feature can be helpful for debugging these rare situations when an AXI interface can not be used.
| Enabled Connectivity | Description | Suggested Use |
|---|---|---|
| AXI4 |
Only the AXI4 path is enabled. The Vivado Hardware Manager only uses AXI for debug core communication. |
Most hardware debug use cases. |
| AXI4, BSCAN Fallback |
Both the AXI4 and the BSCAN pathways are available to access the AXI4 Debug Hub. The Vivado Hardware Manager uses the AXI4 pathway by default. The user can switch to the BSCAN pathway when needed for debugging specific issues. |
Use when debugging an issues such as a system wide AXI timeout where it may be required to bypass the use of AXI temporarily to perform debug but AXI is the desired communication method for debug core connectivity. |
| AXI4, BSCAN Fallback (Select BSCAN Fallback as Default is checked) |
Both the AXI4 and the BSCAN pathways are available to access the AXI4 Debug Hub. The Vivado Hardware Manager uses the BSCAN pathway by default. You can switch to the AXI4 pathway at any time in the Vivado Hardware Manager. |
Use when there is a need for initial debug core communication using BSCAN. An example may debugging a situation where the AXI pathway to the debug hub is not accessible upon booting the device. |
| AXI4 (Unconnected), BSCAN (Default) |
Only the BSCAN pathway is available to access the AXI4 Debug Hub. The Vivado Hardware Manager always uses the BSCAN pathway. |
Use when it is desired to use BSCAN exclusively for
connectivity to the AXI4 Debug Hub. Note: It is not possible to disable
the AXI4 interface on the AXI4 Debug
Hub. However, it can be left unconnected. The designer must still
connect a clock to the
aclk port
and a reset to thearesetn
port. |
Steps to Enable the BSCAN Fallback Feature
- Select the desired connectivity configuration from the table above.
- If an AXI4 Debug Hub has not been manually instantiated in the design, instantiate an instance from the IP catalog. BSCAN Fallback can not be enabled on the AXI4 Debug Hub that is automatically inserted during opt_design.
- Enable one of the four BSCAN ports on the Processing System IP (for example, CIPS, PS Wizard) and
- Instantiate an instance of the BSCAN Switch IP and connect it between the AXI4 Debug Hub and the BSCAN interface on the Processing System IP as shown in the following figure. This is a requirement for the BSCAN fallback feature, even if there are no additional devices on the BSCAN interface.
- If using, connect the AXI4 interface on the AXI4 Debug Hub to the desired interface on the Processing System IP (for example, NoC).
- Connect the
aclkandaresetnports.