RTL Kernel Interface Requirements - 2025.1 English

RTL Kernel Interface Requirements - 2025.1 English - UG1701

Embedded Design Development Using Vitis User Guide (UG1701)

Document ID

UG1701

Release Date

2025-07-16

Version

2025.1 English

To enable the Vitis compiler to connect kernels into the target platform, an RTL kernel must also adhere to the requirements described in the following table.

Table 1. RTL Kernel Interface and Port Requirements
Port or Interface	Description	Comment
Clock	One or more clock inputs. Note: If multiple clocks are used by the RTL Kernel, you are responsible for designing proper clock domain crossing within the RTL Kernel.	At least one clock is required for the kernel.¹ Can be named anything, but must be packaged with a bus interface. Important: All ports in the RTL IP must be associated with an interface when packaging the RTL for use in the Vitis environment. If this is not the case, an error similar to the following occurs: `ERROR: UNDEF When packaging for Vitis, pins that are not part of an interface are not supported`
Reset	Primary active-Low reset input port	Optional port. Can be named anything, but must be associated with a Clock signal through the ASSOCIATED_RESET property on the Clock. This signal should be internally pipelined to improve timing. The signal is driven by a synchronous reset in the associated Clock domain.
interrupt	Active-High interrupt.	Optional port. When used, the name must be exactly as shown.
s_axi_control	One (and only one) AXI4-Lite slave control interface	Required port. The `s_axilite` interface is generally required with exception for some cases using AXI4-Stream interfaces. It is not required for non-software controlled kernels. When used, the name must be exactly as shown, and is case-sensitive. Tip: The address range of the `s_axilite` interface can be edited in the kernel.xml file and repackaged using the `package_xo` command if needed. However, XRT imposes a 64K (16 bit) address range limitation. The tool will return an error if the `s_axilite` interface is greater than 16 bits wide.
AXI4_Memory Mapped Interface (m_axi)	AXI4 memory mapped interfaces for global memory access	Optional port. All AXI4 memory mapped interfaces must have 64-bit addresses. The RTL kernel developer is responsible for partitioning global memory spaces. Each partition in the global memory becomes a kernel argument. The memory offset for each partition must be provided by the SW applications to the kernel through a register in the AXI4-Lite interface. AXI4 memory mapped must not use Wrap or Fixed burst types and must not use narrow (sub-size) bursts. This means that AxSIZE should match the width of the AXI data bus. Any user logic or RTL code that does not conform to the requirements above, must be wrapped or bridged to satisfy these requirements.
AXI4_STREAM (axis)	AXI4-Stream interfaces for one-way data transfers between kernels or between the host application and kernels.	Optional port. Cannot be used with bi-directional ports. Use the STREAM interface template in the Vivado Design Suite. Refer to AXI4-Stream Interfaces for additional information on interface requirements in the Vitis High-Level Synthesis User Guide (UG1399).
The RTL kernel clock frequency specification in the system can refer to Managing Clock Frequencies.

Important: The port names interrupt and s_axi_control must be defined exactly as shown.