[skissane]

> Is this something you have to sign an NDA with Microsoft to get access to the headers and docs for it? Or will I find the headers hidden away in the WDK somewhere?

Turns out the header file is included in the Windows 10 SDK, as km/nthalext.h

Not the very latest version, but someone posted it on GitHub here: https://github.com/tpn/winsdk-10/blob/master/Include/10.0.16...

(You can download the multi-gigabyte Windows 10/11/2022 SDKs to get a more recent one, although not sure if anything has changed.)

Still doesn't seem to be any public documentation. The header includes very detailed comments, but (as you'd expect for header file comments) they concentrate on the nitty-gritty and omit the big picture.

Searching "nthalext.h" on GitHub finds source code for a handful of HAL extensions, so at least there is some sample code to look at. Microsoft has even open-sourced a few – see https://github.com/ms-iot/imx-iotcore/tree/public_preview/ha...

Microsoft used to include HAL extension samples in the Windows 10 driver samples – https://github.com/microsoft/Windows-driver-samples/tree/5b8... – but removed them as part of the Anniversary update – https://github.com/microsoft/Windows-driver-samples/tree/96e...