Can SE Mode help me save time developing just one peice of hardware?

[awmiller]

Hi Folks,

I'm new here. Just downloaded, built and run some of the getting started code over the last few weeks. I'd like to integrate gem5 into my skill set as a Computer Engineer who truly is situated on the border of SW/HW. I develop early FPGA prototypes, integrate lots of systems in many contexts, and work a lot with RF/Microwave, but I also have to continue writing code to support it all and I want to also be proficient with driver software at the lowest levels. Thanks for tolerating my little introduction, heres the real question:

tl;dr:
I want to develop a small system, like a PCIe card, and I want to be lazy and leverage my system to abstract away some of the details like CPU and RAM OS? RootComplex?, but perhaps more importantly also I want to kick the can on those so maybe I can play with them later. Is this a workable usecase for SE Mode?

edit: just reread the SE Mode section, hopefully the spirit of the question is still obvious

Thanks! I'm finding it hard to break out of the available getting started workflows to find the path to what I want to go, but I'll keep learning on the guided path in the mean time. I really appreciate this project, you guys are awesome.

Best,
Andrew Miler
LinkedIn

[abmerop]

Hi Andrew,

It sounds like you are ultimately trying to communicate with devices. With SE mode you will be limited to communication using ioctls and BAR addresses (to use PCI term). Most gem5 configs assume any memory read/write outside of the main memory address range are device addresses, so you can create a SimObject with a port and give it some address range to respond to. If those constraints are fine, then you can go the SE mode route. I usually recommend using FS mode when doing anything with devices but with SE mode you can skip over needing a kernel-mode driver immediately.

For PCIe specifically, the only public upstreamed PCIe devices are the GPU model and IDE controller. There is some ongoing work to improve PCIe support (see #1862 and #2298).

For SE mode here are some pointers that you might find useful:

• https://github.com/gem5/gem5/blob/stable/src/gpu-compute/gpu_compute_driver.cc : This is the SE mode driver for the GPU model
• https://www.gem5.org/project/2022/02/07/lupio.html : If you want a non-PCIe device this is some work done by I believe the project owner's group.