Recently I'm finally able to get a KGPE-D16 coreboot environment that could always boot, although there are a lot of issues and questions. I'm currently using the 4.11 branch as this board has been dropped in the master branch.
The main issue is memory. It seems there are still issues with memory initialization. The Samsung 16GB sticks I currently have (normal or VLP) do not work when using all orange slots, ending in a bootloop due to DIMM training failure (which is the same error I had when I was trying coreboot on KCMA-D8). However, on KGPE-D16, by installing the 8 sticks to the following slots: D1/D2, B1/B2, E1/E2 and G1/G2, I could always get it past the memory initialization, albeit with this error:
"TrainDQSRdWrPos: negative DQS recovery delay detected! Attempting to continue but your system may be unstable..."
This is currently the only combination that could always boot (and with all 128GB recognized). Other combinations I tested either resulted in some "HARDWARE FAULT: HT_EVENT_HW_SYNCHFLOOD" errors which would soft reset before even reaching the DIMM training part, or it entered the DIMM training part but would never complete.
However, the system is currently not at a point that could properly boot to a system (or even a payload) yet. As of yesterday, the only thing I could boot and steadily function is a Menuet64 floppy image.
1. I'm using SeaBIOS master, and have put several floppy images into the CBFS, but it seems to only list the last floppy image I added as a boot option (Ramdisk). It appears multiple floppy images is not officially supported in master yet and I've just located the patch regarding this. I'm still new to SeaBIOS so I'm not sure how to modify configuration/bootorder later on, as I currently don't have a configuration/bootorder file supplied and let it use default values.
2. None of the secondary payloads work. nvramcui hangs with something like "unable to init curs" (I only tried it once and couldn't remember what exactly it is). coreinfo and tint hangs with this "Not enough memory creating EHCI periodic frame list." error. memtest could load, but when it starts testing, it hangs with a glitched screen of blinking characters, among which something like "d h l p t x" could be seen. This also happened when using memtest that comes with the Manjaro Linux boot USB.
3. Initially I had issues with graphical bootloaders like grub, but after disabling bootsplash image as well as not building the seavgabios.bin (by unchecking the "Include generated option rom that implements legacy VGA BIOS compatibility"), I could get Manjaro's graphical grub to load, but still cannot boot to the kernel (XZ-Compressed Data is corrupt). Maybe this is due to memory, as I think the combination I previously mentioned only guaranteed it to go past the training part, but not anything after that.
4. Does this board support any other graphical initialization methods? It seems I can only choose "native graphics init" as well as "legacy VGA text mode" framebuffer. I use SeaBIOS with a dedicated nVidia video card (onboard not used), and it seems without bootsplash image or seavgabios.bin I'm able to load something graphical (such as grub and Menuet64).
5. It seems the board would ramp up the fans to max once it passes the DIMM training and memory clear part (the fans seem to spin at a relatively quiet speed before that, similar to Stock BIOS' Generic profile). As the CPU fans I'm currently using can be really noisy at more than 4300 rpm max, I ended up using a 5.25'' external fan controller (non-PWM) and manually toned it down to an acceptable 2900 rpm (it seems I can't get it to any lower without using a PWM-capable controller). Is there a way to tweak the fan control profiles of the onboard CPU fan ports like the stock BIOS?
This is the first time I ever manage to get a bootable coreboot system, so I'm not sure which part to look into for my issues, especially the RAM part. Is there an up-to-date RAM HCL and guidelines for this board?
At this point, I can always power it on to conduct more tests on this board for any additional logs if needed.