Stuck in Initramfs

custom_board

#41

Hi @Vix

I also saw the Valydate web site was down. A little research shows why https://semiengineering.com/tag/valydate/ They are now part of Mentor Graphics.

The 410c and 820c boards have been through all of the checks that Valydate could have possibly have done. They had access to the IBIS and other models for checking everything that can be checked at pcb layout time. You can get the IBIS models from Arrow and gun them on your own CAD system.

I had concerns when you designed and built your own board, critical to correct operation of the chipset is the power delivery and signal integrity. I hope I pointed out all of the things you have to check when I wrote the design guidelines.

Does your board work if you solder on a 8GB eMMC part? However based on the failure to boot from SDCard, I would guess that the problem is in the Power Delivery Network (PDN) layout.

-Lawrence-
No longer a Qualcomm employee
searching for new employment.


#42

Hello @ljking

Indeed I tried with a 8GB eMMC and the board still fails at boot and falls in initramfs.
So I guess I have to do a deeper design verification by reviewing the processor design guideline document.


#43

Hi Victor @Vix

The other test you could do is to rework a 410c board with your 4GB part. The very first batch of prototype 410c boards we built used a 4GB part, but between the SW team and the marketing team we decided that the board really needed an 8GB part to be a general purpose development board. The other deciding factor for 8GB at the time was the price had dropped so that newer generation 8GB parts were less expensive than the 4GB part.

In your case since the 8GB part doesn’t work on your board I would guess the problem is a layout signal integrity problem which is almost impossible to find with an oscilloscope or software. You need to hunt for it in simulation. Look really hard at impedance and cross-talk in the LPDDR signals. Also look at power distribution impedances. Best of luck finding the issue.

Since you will likely need to rework the PCB, what I would strongly recommend is you get the 410c design files from Arrow, leave the core exactly as-is, then change just the peripheral layout for the items you need.

Another option is to work with one of the Qualcomm partners (Intrinsyc, Inforce, eInfoChips etc.) to design a custom board for you. All of them have done custom boards and made their designs work so I am confident they have the necessary skills, and simulation capabilities. Of course they will likely charge you for their efforts.

Depending on your estimated production volumes buying a System on Module (SOM) from one of the partners might be a reasonable solution. The partners can custom build SOMs with 4GB, but a SOM is almost always more expensive than chips on your own board and not a viable solution if your production volumes are high.

-Lawrence-
No longer a Qualcomm employee
Looking for employment.


#44

Hello @ljking,

Thank you for your message,
The thing is that we already built a custom board with a SoM which was working fine.
Now we tried to build our own board from scratch, based on the 410c design.

Unfortunately we had to use two separate chips for lpddr3 and emmc so I cannot rework the 410c with our emmc chip.

The frustrating part is that I can boot with buildroot and make several stress tests on the memories which all went successfully. The crash when booting the full kernel is probably coming from a transient at boot…


#45

Hi Victor @Vix

The stress tests do run a lot of traffic on the LPDDR, but the traffic patterns (and power usage) are very different than a bunch of apps running on multiple cores. The fact that you can run some tests suggests that you are very close, but not quite good enough. Maybe cross talk between a dynamic power rail and a LPDDR signal? It only takes one single data bit or address line corrupted on one memory transaction to eventually cause a system failure. When you are running stress tests most of the code stays in the cache, and doesn’t need to be re-fetched.

The 410 chipset is used in many cell phone designs, and quite a few of the cell phone OEMs have used separate LPDDR and eMMC chips, so this tells you that it can be done successfully. But of course nobody says it is easy.

The last task the Qualcomm internal team completed was verification of a 410c layout variant that used separate LPDDR and eMMC chips. The design is complete, and verified on physical hardware, however Qualcomm disbanded the team before the design was released. The completed design is in the Qualcomm system, and Arrow or one of the partners may be able to get the design files for you. The downside to the internal design is it required 2 additional layers to fully meet the signal integrity and power delivery requirements.

-Lawrence-
No longer a Qualcomm employee
Searching for employment.