NixOS on ARM/UEFI

← Back to NixOS on ARM

Note: The page is written assuming AArch64. It is possible that following most of these instructions for armv7l would work just as well, but armv7l support in NixOS is not at a point where doing so will be nice.

This section of the NixOS on ARM documentation aims to document as much as possible about booting any ARM boards using UEFI. This will be written with a heavy bias about Single Board Computers (SBCs), as this is where booting is seen as complicated, cumbersome, when not described as impossible.

The Basics First

Target Support

Some things will not be specific to UEFI. For example, board support by the kernel used. This is written assuming that mainline Linux works enough on the target system so that you can install from the generic iso image.

Just as you could on x86_64 if your platform required it, you can build a customized iso image. Explaining this is out of scope for this article. The same pitfalls apply. For example, the generated configuration will not take into account configuring the customized kernel.

Initial Boot Firmware

Let's define what an Initial Boot Firmware is. It is a generic term I'm using to describe the first thing the CPU starts at boot time. On your typical x86_64 system, it would be what was previously called the BIOS. Now often diminutively called by the name EFI. This is what initializes enough of the hardware so that the operating system can start. Additionally, it often provides facilities for the user to do basic configuration, and manage boot options.

In the ARM with SBCs landscape, U-Boot is the de facto solution for the Initial Boot Firmware. Though U-Boot is confusingly, but rightly, often referred to as a Boot Loader. U-Boot plays double duties often. It is tasked with initializing the hardware, and often also used to handle loading and booting the operating system.

UEFI

The Unified Extensible Firmware Interface it not in itself a tangible thing. Wrongly abtracted, it is a specification used to provide an interface to describe a standard boot process, including an environment before the operating system starts, and protocols for operating systems.

There are multiple implementations of UEFI. Vendors like American Megatrends, Phoenix Technologies and Insyde Software may have produced the one on your personal x86_64 machine. TianoCore is the reference UEFI implementation, and Open Source. Luckily enough, U-Boot implements enough (and a bit more) of the UEFI spec.

SBBR? EBBR?

Other than letter salads, they are Server Base Boot Requirements and Embedded Base Boot Requirements. Two specifications for ARM. If your target is in compliance with either, booting with UEFI should already be supported. With the minimal UEFI support in U-Boot, targets that were not made to be EBBR compliant can be made compliant, or be close enough for what it matters.

UEFI, on my SBC???

Believe me or not, it's more likely that you can, if your SBC is well supported by mainline U-Boot. U-Boot provides enough UEFI to comply with EBBR, which in turn is enough to allow us to boot the AArch64 UEFI NixOS iso, and with almost no differences compared to the x86_64 guide, simply follow the installation instruction to boot into an installed system.

Getting an Initial Boot Firmware

This article or section needs expansion.

Reason: for now, left as an exercise to the reader... More will be coming soon. (Discuss in Talk:NixOS on ARM/UEFI#)
Please consult the pedia article metapage for guidelines on contributing.