I am trying to use a 4GB eMMC-less Radxa CM3 on a Turing Pi 2 board, which supports the Raspberry Pi CM4. If the Radxa CM3 is indeed compatible with the RPI CM4, this should be possible.
Over on Github, @RadxaYuntian said that first I need to flash SPI with the bootloader. But where exactly can I find instructions for doing so? On Radxa’s wiki there is a page about flashing the SPI on Radxa’s CM3 IO board, but nothing about using the RPi IO board or even other boards.
Are we then to assume that you absolutely need the Radxa CM3 IO board? If so, shouldn’t this “little” fact be mentioned in large bold letters to any buyers of the CM3?
The first thing you should do is to check if your CM3 module has “SPI-Flash” soldered.
There are multiple reports that such a thing “SPI-Flash” is not soldered.
And, in fact, even the one I owned didn’t have it soldered.
Even on the wiki page, there is a mix of soldered and not soldered items.
About a year ago, When I asked the retailer,
I was told that the photos showing “SPI-Flash” installed were only of very early models, and that current models do not have it installed.
In my case, I soldered the parts I had on hand myself, but I don’t think that’s possible for everyone.
Thanks for your reply, @t4_4t. Assuming that the SPI flash and “SPI Flash disable button” are in the positions shown in the image on this wiki page, then my device does not have one. Should I just ignore all the steps relating to flashing?
Also, I’m a bit confused by your mention of soldering parts. Are you saying that I bought a Radxa CM3 which cannot even be used before soldering missing components?! I feel like there’s critical information about the CM3 which Radxa completely fails to advertise!
In my case and many other reports, neither ① nor ② are soldered.
Same as the photo below.
① SPI Flash disable button
②SPI flash
In your case, it seems that only ② is soldered.
If you write wrong data in this state, you will be in the same situation as if his BIOS of a “standard x86-PC” would be destroyed because “SPI-Flash” cannot be disabled.
In other words, the CM3 module itself is literally a brick…
If you have electronics experience, you can use your existing Switch instead. (Short it with tweezers, etc.)
---- @ eMMC less module —
If the serious problem of not being able to boot from the SD card has been resolved, the write “SPI-Flash” operation itself is sufficient with a simple “dd command” on Linux.
If your CM3 module does not have the above issues fixed, the only option is to use the “Radxa CM3 IO Board”.
In fact, it is no exaggeration to say that on the genuine Pi4 original board, the CM3 cannot boot from the SD card and is not compatible at all.
(It’s a real brick because it can’t even boot.)
Since it doesn’t work on the genuine Pi4, most similar products that claim to be Pi4 compatible will have the same result.
My CM3 doesn’t seem to have either ① or ②. I have tried copying various images onto an SD card, but it does not boot with any of them. Does this mean that the CM3 I have is not compatible at all, and that therefore can only boot from the Radxa IO board?
I really wish someone from Radxa would clear this up. I have been wasting my time for months due to their obfuscation!
It seems that your “CM3” is the same as the photo in the URL I provided, And also the one I have.
If so, there’s no point in doing anything.
There are already many reports that support this.
No matter how much you replace the “SD-Card” or Image,
The SD-Card cannot be read at boot time due to a hardware problem.
(In other words, it is not possible to boot from S"D-Card")
>> @RadxaYuntian said that first I need to flash SPI with the bootloader.
I saw this a long time ago, and I thought it was a truly bizarre claim.
This is because, The “CM3” their sell does not have “SPI-Flash” soldered in it.
How can We run “CM3” without “eMMC” variant on a genuine Pi4 carrier board ?
There is a thread discussing this, please refer to it.
(Even if it is impossible to modify the hardware,
Why we can’t boot ? You can understand the that reason.)
It is relatively easy to modify a genuine Pi4 carrier board,
But it is difficult to modify many similar products that claim to be Pi4 compatible.
Thanks again for your reply, @t4_4t. You mentioned earlier that you soldered some parts. Is it possible to solder one or more components to the CM3 to make it compatible with the RPi CM4 IO board?
In each “CM3”, both parts ① and ② are soldered. (I already own these parts).
All carrier boards except “Radxa CM3 IO Board” have the modifications described in above my posts.
Therefore, in my case, “SPI-Flash” is not essential to boot from “SD-Card”.
I added “SPI-Flash” simply because I personally have another purpose.
Also, in case of “CM4-IO-BASE-C”, it is extremely difficult to modify it.
You need to have the skills, tools, and parts to solder only one specific pin on the “⑬ B2B connector 1 (J69)”.
In fact, I decided “this is impossible for me” and used another method.
I assume your interest is in “is it possible to do that with the Turing Pi 2 board ?”
In that case, the key is the “CM4 Adapter”. (included or sold separately)
Unfortunately, I can’t judge whether it is possible or not, since there seems to be no schematic available.
Flashing SPI does not require Radxa CM3 IO board. You connect to RPi CM4 IO’s micro USB port and you should be able to proceed as normal.
The SPI bootloader that allows to boot from microSD is relatively new, so the documentation for it is currently missing.
If you CM3 does not have SPI soldered, then obviously you can’t flash it. But that is on the production side of the thing and it’s out of my responsibility. I’ll need to clarify what’s going on, but if your CM3 does not have eMMC or SPI, then it cannot boot from microSD on RPi CM4 IO.
Edit: Currently the CM3 production requires either SPI or eMMC to be present. For earlier batches this policy was not established so there might be eMMC and SPI less CM3. If you purchased CM3 recently and got neither storage please contact your seller for RMA.
