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Frequently Asked Questions

Licensing and Suscription Plans

Can I host my own airhdl?

Yes. Besides a few technical requirements (your server will need to provide Java 8, and a MySQL database), you will need to license a self-hosted version of airhdl, whose price starts at US $2500 per year. Please contact for more information.

Does the command-line generator require internet connectivity?

No. The command-line generator that comes with the Professional CL plan does not "phone home" and does not require any internet connectivity.

Does the command-line generator perform license checks on the internet?

No. The command-line generator that comes with the Professional CL plan only checks a local license file.

Can I still use the command-line generator after my Professional CL subscription has expired?

No. The command line generator license expires the same day as your Professional CL subscription. Once you have renewed your Professional CL subscription, you will be able to generate a new license file for the command line generator.

Can I upgrade my Professional plan to the Professional CL plan?

This operation cannot currently be performed in the user interface, but we'll be happy to do it for you. Please contact us at

User Management

How can I change my password?

To change your password, Click on the Account icon in the top navigation bar to show the Account view. Click on the gear icon and select Change Password in the drop down menu.

Editing Register Maps

Can I set the register width to a value other than 32 bits?

Currently, airhdl only supports registers with a fixed width of 32 bits. This, however, does not mean that every register will utilize 32 flip-flops in the synthesized logic. Only the register bits that correspond to actual fields will be mapped to actual flip-flops.

If your project could benefit from data widths other than 32 bits, please let us know by voting for that feature.

How do I change a register's address offset?

When you create a new register, airhdl automatically sets its address offset to the next available location in the register map's address space. To change the address offset of an existing register, open the Edit Register dialog and enter the register's new address offset.

As an alternative, you can also recompute the address offsets for all the registers in a map by clicking on the Auto-compute register offsets button at the top of the Registers table. This operation, however, cannot be undone.

Xilinx SDK

How can I read or write registers in Xilinx SDK or Vitis for debug purposes?

You can do that in the XSCT console. If it's not already visible, you can bring up the console using the Xilinx -> XSCT Console menu entry. In the XSCT console, you can use the mrd and mwr commands to respectively read and write memory locations, e.g. mrd 0x40000000.

Supported Interfaces

Does airhdl support other interfaces than AXI4-Lite?

The current version of airhdl only supports AXI4-Lite interfaces. Still, airhdl register banks can easily be connected to other bus systems (such as Avalon) through a corresponding bridge component. As an example, we have created an open-source SPI to AXI4-Lite Bridge, which you can use to connect airhdl register banks to any microcontroller over the SPI bus. Please let us know if you'd like to see airhdl support other bus interfaces.