Example projects for microcontroller PCIe?

I've seen a lot of job postings lately that have a good skill fit for me but they require PCIe device firmware experience. If my current work involved this I'd just volunteer to help, but I don't work with anyone who knows how to do it either. I've been trying to find examples, but I haven't found anything aimed at being an introduction, and working from the raw PCIe standard is a steep learning curve.

Can anyone suggest a project that is available to use as an example? Linux or windows drivers are fine. I can work with ARM cotex M0, M3, M4, and M7. I'm glad to get a new programmer and some MCUs if needed. On hand I have some Pic32mx controllers, several psoc 5lp chips, and various st32 microcontrollers.

Thanks for any advice!