Hi, I recently received my Depthai with Rpi CM4. While I was running examples from the depthai-python repository, I would get Communication exception from time to time. For example, I get > inDepth = q.get() # blocking call, will wait until a new data has arrived > RuntimeError: Communication exception - possible device error/misconfiguration. Original message 'Couldn't read data from stream: 'disparity' (X_LINK_ERROR) while running 03_depth_preview.py, and get > track = tracklets.get() > RuntimeError: Communication exception - possible device error/misconfiguration. Original message '[json.exception.parse_error.110] parse error at byte 1: syntax error while parsing MessagePack value: unexpected end of input' while running 29_2_spatial_object_tracker.py. Is there anything I can do to check what is wrong? Thanks

Hi @"pikelcw"#251 , Sorry about the trouble here. We recently discovered a stability issue on the Pi series with our Gen2 API (which is our mainline API) that we've been feverishly trying to solve. https://github.com/luxonis/depthai/issues/354 So I think this is what you are running into. @"GergelySzabolcs"#62 I think got to the bottom of it yesterday, and is working to implement a fix. In the time being, depending on what you are planning to accomplish, you could use our Gen1 API. We have tested that (to make sure it doesn't suffer from the same issue) and it will run for 2 days straight without an issue. If that's of interest, see below for instructions: To run gen1, clone this repo: https://github.com/luxonis/depthai And then checkout `gen1_main`. And then you can run `python3 install_requirements.py` And then to run the equivalent of `29_2_spatial_object_tracker.py`, you can run: `python3 depthai_demo.py -s metaout previewout depth object_tracker -bb -ff` [URL=https://i.imgur.com/vU0TOIG.jpg][IMG]https://i.imgur.com/vU0TOIGh.jpg[/IMG][/URL] Now that we think we know what the root cause is, we are working to fix it in Gen2, but we don't yet have a timeline on that. This bug went back to the very beginnings of Gen2, but didn't actually become evident until recently. Thoughts? Thanks and sorry again about the trouble here. -Brandon

Hi @"Brandon"#p1108 , Thank you for the response. For now, Gen 1 should be enough for my purpose! I have another unrelated question. My depthai's rpi won't boot if I just plug in the 5V. I need to either plug in an HDMI, or plug in the micro USB on the side then unplug it to boot. Is that how it is designed to work? Or is that some software setup? Thanks

Hi @"pikelcw"#p1110 , Thanks. Yes, so that's actually a setting in the Raspberry Pi itself. I thought we had changed it by default, but apparently did not. So the Pi 4 series will actually boot, but not launch pretty much everything if there is no HDMI plugged in. The why is that with no monitor connected the Pi will not launch the graphical environment. With Pi 3 had composite enabled by default, which was equivalent of having a monitor plugged in, even if no monitor was plugged in. See here for the fix: [https://github.com/luxonis/depthai-hardware/issues/45#issuecomment-788632720](https://github.com/luxonis/depthai-hardware/issues/45#issuecomment-788632720) Thoughts? Thanks, Brandon

Hello @"Brandon"#4 , I had changed these settings but it still does not boot. After changing the settings and plugging in 5V, only the PWR LEDs came up, other LEDs did not. And also the USB wifi dongle's LED did not turn on. [URL=https://i.imgur.com/vBEG0hH.jpg][IMG]https://i.imgur.com/vBEG0hHh.jpg[/IMG][/URL] Anything else I can try? Thanks

Hi @"pikelcw"#p1115 , That's odd. I think my unit (without the settings changed) does the same thing - at least no activity light - when there is no HDMI plugged in. We'll try to reproduce. Sorry about the trouble here. -Brandon

Confirmed that my Pi CM4 DepthAI boots with monitor connected by does not boot w/ no monitor. Trying some things...

Hrm... none of the tricks that worked before are working. I wonder if the new version or Raspbian changed this boot behavior for Pi 4.

Searching... https://raspberrypi.stackexchange.com/questions/109279/pi-4b-wont-boot-without-hdmi-cable-plugged-to-monitor

Yes, I can't figure out why this doesn't work anymore w/out a monitor plugged in. We definitely had this working before.

Alright, I finally got it. To get the Pi 4 to boot up completely without HDMI attached, adding this to /boot/config.txt did the trick: `enable_tvout=1` Please note though that for me this actually completely _prevented_ HDMI from working at all. But I think for the use-case here, that's fine. Thoughts? Thanks, Brandon

Communication exception

Brandon

Hi pikelcw ,

Sorry about not circling back. Have been underwater overall. I could not figure out how/why this is happening. It seems to actually have something to do with the CM4 modules themselves, as far as I can tell. And specifically, if they are eMMC or uSD.

We can send you one of these to address it for sure if that works for you:

If so please shoot an email to support@luxonis.com and we'll get one sent your way.

Thanks,
Brandon

pikelcw

Hello Brandon

I have tried the exact same HDMI Dummy Plug. But I am still not able to boot with that plugged in.
Any other suggestions?

Thanks

Brandon

Shoot. So odd. We could try sending you another one? I'm not sure what makes some refuse to boot w/out HDMI and others don't have a problem.

pikelcw

Brandon
Do you mind sharing your whole /boot/config.txt?
I want to double-check if I have changed anything that I should not.

Thanks

Brandon

pikelcw

Great question. I trashed mine unfortunately so I don't have working config right now. Was testing something else and corrupted the SD-Card. Will ask for others on the team to share.

Luxonis-Lukasz

@pikelcw I tried to use the CM4 without HDMI and couldn't boot it up too, same after sudo rpi-update. Also hdmi_safe or hdmi_force_hotplug flags didn't work, tried disabling desktop GL driver, setting default desktop resolution (both via raspi-config or manually editing /boot/config.txt ) or even disabling HDMI completely and setting the default to composite output.

I'll investigate with the team further and circle back with more details. Seems that the OS is not booting at all without HDMI, but here is the /boot/config.txt I used if needed for reference

Brandon

As another update it is seeming that this does depend on the CM4 module itself. With a given module we could not get HDMI boot on one module, and it would boot on the other - and this followed the CM4 module itself - no matter what Luxonis board we put it on. Even across different revisions of the Luxonis carrier board.

Test we did below:

Two OAK-D-CM4 (DM1097_R0M0E0), both equipped with the same CM4-Lite WiFi capable Raspberry CM4 modules.
I have tested both with the same uSD card one after another:

first OAK-D-CM4 1 with CM4 Lite module 1 I was able to boot it without the HDMI attached, and the LED works as on the CM3 in your case.
second OAK-D-CM4 2 with CM4 module 2 won't boot and the ACT LED does not blink at all as you observed (tested with the same uSD)
after this test I swapped the CM4 modules on both devices and now the first device 1 with CM4 module 2 won't boot and the device 2 with CM4 module 1 will

So it has to be related to CM4 module, not sure but might be related to CM4 bootloader as there probably are some deviations across the different CM4 modules.

We're wondering if some of the modules simply need a bootloader update. We're investigating in this direction:

https://github.com/raspberrypi/rpi-eeprom/blob/master/firmware/release-notes.md

pikelcw

Hello Brandon

I just tried using the same CM4, that was on my OAK-D-CM4, with another carrier board(PITray mini). And it booted without HDMI connected to it.
Does that mean that it is not the bootloader's issue?

Thanks

Brandon

pikelcw Oh that's great to know!

Can you share a link for purchasing that one? We'd like to compare.

pikelcw

Brandon
Sorry for the late reply. Here's the link https://www.dfrobot.com/product-2196.html.

David
Thank you for the update. How can I get a reworked unit?

David

We looked into this issue thoroughly today and we found out that it is actually not related directly to the HDMI connected or not, as we first thought that if it is not a bootloader it must be something with HDMI interface signaling/detection.
But the issue really lies somewhere else, that is in the power up procedure. We found out that Raspberry Pi CM4 datasheets states that

All pins should not have any power applied to them before the +5V rail is applied.

We come to that when seeing that device boots up successfully w/out HDMI connected, if the PSU is immediately reattached to the barrel jack connector after disconnection (in ms), or sometimes when PSU is first connected to the jack and after that to wall plug.

To get to the point; we are using external power supply for 3V3 rail which is connected to the RPi CM4 module over pull-up resistors on the input/output signals going to/from the CM4 module.
After 5V is applied, it seems that the 3V3 rail rises to quick (_1ms) and kind of a latch-up happens.
We modified the hardware enabling the PMIC with 3V3 generated from RPi, that way ensuring 3V3 power rail voltage will always rise later than 5V is supplied. That resulted in all boards boot up without HDMI connected, no matter the version,, CM4 module variant used... It boots, if we are using CM4 Lite with uSD and booting from there, or if we attach the CM4 with eMMC, booting from eMMC.
Modification that works for now: removed the 10k PU from EN pin on PMIC, and connected EN pin to CM4_3V3 rail.

We believe that the reason for that some of the CM4 modules booted - no matter what Luxonis board we used it on (Luxonis carrier board) while some didn't, is that we were/are really on the edge here with this issue.
On the other hand and we are not aware of the exact boot procedure on the CM4 and what causes the latch before boot, so can not explain the real reason behind this.
Nevertheless in the Raspberry PI compute module datasheet is clearly stated that none of the pins, on a CM4 module, should have any power applied to them before the +5V rail is applied. We are also not sure about why connecting the HDMI cable solves this issue, it could be that the CM4 has different boot procedure when HDMI is connected or not.

To close that up, we will update the design and we can also offer sending a reworked unit for now for everyone affected by this issue.
We are sorry for any inconvenience brought in by this issue.

Best regards David,
Luxonis lead EE

Brandon

pikelcw

Sorry about the trouble here.

Could you please shoot us an email at support@luxonis.com and we'll get a new unit shipped to you ASAP.

Thanks,
Brandon

pikelcw

Brandon
Just sent it out!
Thank you!

Brandon

(We'll rework a unit and send it to you... future production will have this design fix.)

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