demedeirosa
Posts: 17
Joined: Wed Jul 11, 2018 1:57 pm

Troubleshooting CM3/CM3L custom PCB

Fri Jul 27, 2018 12:38 pm

Hi all,

I just put together my first CM3/CM3L carrier PCB. I'm having an issue getting it to boot correctly. Heres a video of the boot LED, it doesnt appear to match the LED on the RPI carrier PCB. In addition, I see no activity on the USB bus. On the RPI IO pcb I see activity immediately.

https://photos.app.goo.gl/L1rMMSZANbvZianH7

I corrected a few issues with the board, stupid mistakes of course... The 1.8V regulator appears to not be able to handle the load on it, I bypassed it, and connected it directly to my bench supply. I power up my PCB with 24V, it creates 3.3V for 3V3/VBAT and it creates 5V for USB Host. I then manually enable the 1.8V on the supply. Could this significant delay be an issue?

The only other issue I can find is that GPIO28,29 do not have pull-ups/pull downs on them. I am planning on adding this today when I get to the hardware. Could this cause the failure?

I can post a schematic later on today if it would help.

Thanks!!

demedeirosa
Posts: 17
Joined: Wed Jul 11, 2018 1:57 pm

Re: Troubleshooting CM3/CM3L custom PCB

Sat Jul 28, 2018 10:52 am

Hi all,

Ended up determining it was an error on the PCB. USB_DP and USB_DM were swapped. A little bit of wire wrapped wire solved the problem until we can send out new boards.

Here's another question, it seems to take a significant amount of time for the system to boot on my PCB vs the IO board. Is there anything in particular that could cause this from a hardware perspective?

Thanks!


John Westlake
Posts: 107
Joined: Thu Nov 09, 2017 4:34 am

Re: Troubleshooting CM3/CM3L custom PCB

Sat Jul 28, 2018 1:43 pm

demedeirosa wrote:
Sat Jul 28, 2018 10:52 am
Here's another question, it seems to take a significant amount of time for the system to boot on my PCB vs the IO board. Is there anything in particular that could cause this from a hardware perspective?
A common issue for first time CM3 hardware developers - I'm betting you missed a pull-up resistor on the HDMI_SDA line :)

See this Thread:-

viewtopic.php?f=98&t=115095

demedeirosa
Posts: 17
Joined: Wed Jul 11, 2018 1:57 pm

Re: Troubleshooting CM3/CM3L custom PCB

Sun Jul 29, 2018 9:34 am

Interesting! I left all HDMI lines unconnected since I am not using them, and it mentions to leave them open in the datasheet. Any other surprises to be aware of?

John Westlake
Posts: 107
Joined: Thu Nov 09, 2017 4:34 am

Re: Troubleshooting CM3/CM3L custom PCB

Sun Jul 29, 2018 6:32 pm

Non come to mind, but just watch CPU throttling due to overheat - IMO the CM3 REALLY requires a heatsink.

IMO, the CM3 is unusable without a heatsink - even unpacking an OS install can trigger thermal throttling... Don't fall into the trap as we did that that as a heatsink is not required for the RPi3 you will be OK not using a heatsink on the CM3... the thermal dissipation of the CM3 is much worst then RPi3.

If your using the LAN9514 then you will find its thermal dissipation much higher then on the RPi3 board as the LAN9514 's internal linear 1.8V LDO's are disabled and powered from the PI3 local 1.8V switching regulator.

There is an undocumented test pin on the LAN9514 to disable its onboard LDO's, but I can only presume that MicroChip have undocumented this mode as PSU noise on these 1.8V rails will impact the phase noise of the LAN9514 Ethernet and USB PLL"s circuits and that MicroChip felt it easier to avoid facing constant customer support issues regarding marginal performance of the USB / LAN.

Also, a common error is to missout the 1M resistor across the 25M Crystal on the LAN9514 (this 1M resistors bias the oscillator circuit into its linear region) - the LAN9514 Datasheet is non too clear...
Last edited by John Westlake on Mon Jul 30, 2018 2:49 pm, edited 3 times in total.

demedeirosa
Posts: 17
Joined: Wed Jul 11, 2018 1:57 pm

Re: Troubleshooting CM3/CM3L custom PCB

Mon Jul 30, 2018 12:51 pm

Thanks for all of the help! The HDMI_SDA pull up was the issue, threw a 10k pull up on it and it booted up immediately with applied power. I wonder why this isnt called out in the datasheet?

Thanks for all the LAN info as well. This project is pretty straightforward and doesn't require a LAN connection. I am however using a DPI24 screen, so I will look into the thermal considerations. Not sure if that will create any significant heat. Thankfully our project is not terribly power intensive. The CM3 was just a good platform for a quick prototype run.

Thanks!!!

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