JTAG and Boundary-Scan

Versal ACAP Technical Reference Manual (AM011)

Document ID
AM011
Release Date
2022-04-26
Revision
1.4 English

The Versal ACAP architecture is compatible with the IEEE Standard Test Access Port and Boundary-Scan Architecture (IEEE Std 1149.1) and includes all the mandatory elements defined by the standard. These elements include the TAP, TAP controller, instruction register, instruction decoder, boundary register, and bypass register. Versal ACAPs also support a 32-bit device identification register and a JTAG configuration register that adds additional readback and configuration JTAG capability.

The primary debug access port is the JTAG interface. The JTAG chain order in the Versal ACAP is fixed with the DAP controller followed by the TAP controller as shown in the following figure.

Figure 1. JTAG Chain

The JTAG dedicated I/O supports boundary-scan operations, status register access, PL readback, and a single-stepping hardware analyzer in the PL and AI Engine. The JTAG interface provides base debug to assist with board or device bring-up issue isolation.

If JTAG is disabled, via the JTAG disable eFUSE, only the IDCODE JTAG instruction is available. This is a permanent setting and cannot be reverted. See the Versal ACAP Security Manual (UG1508) for the production readiness of the desired security feature, as well as its detailed usage instructions. This manual can be downloaded from the Design Security Lounge.
Important: An active NDA is required for access to the Design Security Lounge.

If the JTAG disable eFUSE is not set, on power-up, the default boot mode is secure and the JTAG interface accepts the base JTAG instructions regardless of the boot mode. For non-secure boot, after the boot is complete, successfully or unsuccessfully, the full suite of extended JTAG instructions are enabled. For secure boot, if the boot is completed successfully, the authenticated software is capable of enabling the extended JTAG instructions. In the event of a failed secure boot, the JTAG capabilities are dependent on how the device was provisioned.

The following figure illustrates the JTAG interface protections, as well as when the base JTAG instructions or full extended instructions are available.

Figure 2. JTAG Interface Protections