Recommended CM4 for Stereo Pi v2?

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Dubrawski
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Recommended CM4 for Stereo Pi v2?

Post by Dubrawski »

Hello,

I hope to make a 3D camera using Stereo Pi v2. I have looked at the wiki, forum and crowdsupply page, but couldn't find conclusive information regarding recommended model of the CM4. What are minimum and recommended amounts of RAM to run SLP2? Minimum and recommended MMC size? Which is the fastest memory to boot the OS and start the software, MMC, SD card or USB stick?

Also, what if I would like a nice case - is the only option to create and 3D-print it myself, or are there some plastic or metal universal cases (or some other idea)? I've noticed HQ Metal Housing and I'll probably get that, but it's only for the lenses.

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Realizator
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Re: Recommended CM4 for Stereo Pi v2?

Post by Realizator »

Hi Dubrawski,
Our choice is CM4 Lite (now eMMC) + Wireless (BT and WiFi) and 2Gb RAM, or "CM4102000" according to RPF.

RAM:
Actually, for SLP even 1 Gb is enough. We choose 2Gb as it is better for the OpenCV (compilation from source).

WIRELESS:
Good thing and the wireless module is just $5 more expensive than non-wireless.

eMMC:
We prefer to use a non-eMMC module (or Lite), as in this case you can use a micro SD like with the classic Raspberry Pi. Easier image upload, easier access to your data (config files and photo/video records).
eMMC is fast, but you can use a high-speed micro SD to get the same performance.

As for the case - our kits include the minimal enclosure for a quick start. Most users prefer to develop their own 3D printed cases. You can use 3D models of our boards from our Wiki to create your own.
Eugene a.k.a. Realizator

Dubrawski
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Re: Recommended CM4 for Stereo Pi v2?

Post by Dubrawski »

Thank you Realizator. It seems the CM4 you recommend would be the best option for me too.

Regarding USB ports, is any of them USB 3.0 capable? I could not find the schematic, but just to confirm my understanding, I suppose PCIe is not connected anywhere; and if I get a module with MMC, then I can't use the micro SD slot?

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Re: Recommended CM4 for Stereo Pi v2?

Post by Realizator »

Hi Dubrawski,
CM4 has the only USB port exposed, and this is USB 2.0 port. We added the USB HUB chip to split this port into 3 USB ports (two of them are USB A, and the 3rd one is on the pins for advanced users). You can take a look at the "No bottlenecks!!! SPEEEEEEEEEEED!!!!!!!!" section in our article, where we put a connectivity diagram of CM3 and CM4.
Raspberry Pi 4 is using VIA chip PCIe->USB 3.0. This chip is not available in small quantities from distributors. Looks like Raspberry Foundation has some special agreement with VIA. We decided to not add this expensive and tricky part to StereoPi v2, as CM4 has all bonuses we need in comparison with the CM3. I mean Gigabit Ethernet and WiFi, which do not have the bottleneck like it was on CM3.
Eugene a.k.a. Realizator

Dubrawski
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Re: Recommended CM4 for Stereo Pi v2?

Post by Dubrawski »

Thank you. I was hoping PCIe could be used to connect a SSD or a fast USB 3 memory stick, but while nice to have, I don't really need any of that. A micro SD will be perfectly fine. I think I'll only go for a 4 GB lite module, so I have an option of creating a small ramdisk to temporarily cache images or launch programs faster. (8 GB ones don't seem to be available anywhere, which makes it easier to decide.)

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Re: Recommended CM4 for Stereo Pi v2?

Post by Realizator »

Using 4Gb for ramdisk is a good approach. In all our experiments recording of encoded video and images is not a bottleneck, but if you are planning to record RAW video or photo - this might be critical.
As for 8Gb CM4 - as I know, these modules are produced by Raspberry Pi for B2B customers only, and available in bulk (with a minimum of 1400 pcs per order).
Eugene a.k.a. Realizator

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