Intel Motherboards - Above 4G MMIO Resource Allocation

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Above 4G MMIO Resource Allocation

Printed From: ASRock.com
Category: Technical Support
Forum Name: Intel Motherboards
Forum Description: Question about ASRock Intel Motherboards
URL: https://forum.asrock.com/forum_posts.asp?TID=17832
Printed Date: 21 Dec 2024 at 10:31pm
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com

Topic: Above 4G MMIO Resource Allocation

Posted By: bgelb0
Subject: Above 4G MMIO Resource Allocation
Date Posted: 18 Jan 2021 at 12:49pm

Hello -

I am trying to use an ASRock J3355M motherboard connected to multiple GPUs. When I connect 3 or more GPUs, the system does not boot (no video output, can't see BIOS messages etc).

With two GPUs or one it boots fine.

I suspect what is happening is that the BIOS is probably trying to allocate the PCIe BAR address ranges below the 4G limit (and with more than two cards, runs out of address space). I note that when I use 2 or fewer GPUs and the system does boot, I can see via lspci that all of the BAR windows are located below 4G.

I went looking around for an option in the BIOS configuration called "Above 4GB MMIO BIOS Assignment" that is present on other ASRock boards (including the J3455 Pro BTC+, which is very similar) but does not seem to be present on the J3355M.

Is there some way to expose this or permit PCIe devices to get allocated above 4G? Is there a test BIOS or something that could enable this option?

Many thanks.

Ben