Omega2 vs. Linkit™ Smart 7688



  • Does anyone have any practical experience with both of them?

    LinkIt™ Smart 7688



  • No experience, but it has pretty good tutorials for OpenWRT, very easily applicable to LEDE.



  • I have both of them. The LinkIt smart can be used easily with no dock, has onboard regulators and two micro usb ports - one for power and one host port. There is a dock which would give you ethernet and audio in/out.

    The LinkIt is larger than the Omega2s. Specs are similar to Omega2+. Thy have a model with onboard Arduino, I don't have experience with it.

    The LinkIt is more expensive than the Omega2s at $13. It has older software kernel 3.18 from the OpenWRT branch. Omega is based on LEDE, kernel is 4.4. LinkIt has opensource bootloader, the Omega does not. I prefer the uBoot from the LinkIt - it is faster to flash from the USB drive and has richer functionality.

    I was able to get the i2s audio working with the LinkIt, not yet with the Omega2. Other than that they are both very similar. Support is sparse on both. LinkIt documentation is hosted on the MediaTek site, but forum questions are met with silence or vague answers - the community is smaller than the Omega.

    Forgot to mention, the Omega2 is running way hotter than the LinkIt smart. Not sure why but it makes quite a bit of heat.



  • @Ghent-The-Slicer Thank you very much. Just one more question: what happens with the push of when you press down the 'MPU Reset Button'.



  • @György-Farkas said in Omega2 vs. LinkIt™ Smart 7688:

    @Ghent-The-Slicer Thank you very much. Just one more question: what happens with the push of the MPU Reset Button.

    That grounds the SoC's reset line when pushed, causing a hardware reset.



  • @Chris-Stratton
    Yes, I have seen. LinkIt Smart 7688 has a very nice schematic.
    What happens in reality - that was the question.
    It freezes too like Omega2+ or it can perform a normal reboot.



  • @György-Farkas said in Omega2 vs. LinkIt™ Smart 7688:

    @Chris-Stratton

    It freezes too like Omega2+ or it can perform a normal reboot.

    No. Unlike the comparable memory size Omega 2+, the Linkit smart has a correctly selected model of 32 megabyte flash chip which starts up in 4-byte mode, the MT7688 is strapped to expect that and by all appearances 4-byte mode is never left, so the system can restart when reset by any of the reset input, watchdog, brownout, etc, rather than only on power on or when prepared for restart by software, as the erroneously selected flash chip on the 2+ requires. Note that the flash address mode problem is is unique to the 2+, the plain Omega 2 should not share it either as the entirety of its smaller flash chip can be accessed in the 3-byte mode in which it starts.



  • @Chris-Stratton So, do you say: it's a pure hardware complication of Omega2+, there is no and never will be any solution by software, don't you?



  • @György-Farkas said in Omega2 vs. LinkIt™ Smart 7688:

    @Chris-Stratton So, do you say: it's a pure hardware complication of Omega2+, there is no and never will be any solution by software, don't you?

    Indeed, unless you replace the flash chip with a more suitable one and change the MT7688 strapping to match, the Omega2+ is going to be confined to situations where occasionally cycling the power to get it unstuck after any unprepared reset, is acceptable.

    Only other options I could think of would be to soft-downgrade it by making custom software that leaves the flash in 3-byte mode, basically cutting the storage size back to that of a plain Omega2 (but leaving the larger RAM), or else try to find some super-clever series of startup bytes that works even when read offset-by-one in position under the wrong addressing mode. But unless the mips startup is more flexible than I imagine, that's likely not possible.

    Basically, to offer an MT7688 system in both 16MB and 32MB flash sizes, they needed to not only change the flash chip to one that could startup and always thereafter operate in 4-byte- mode, but also place a pulling resistor in one of two different places compatible with the addressing mode of the chip installed. The problem comes from trying to do a software mode switch. But doing it the right way in the next production lot would be a trivial change.



  • @Chris-Stratton Thank you Chris. I'm not too cheerful. :disappointed:

    I think from the "If you have an issue with your Onion products" box this line is missing:
    Categorized Well-Known Bugs, Unsolved Issues are available here <link>



  • A few things I forgot to mention. The LinkIt smart user a proprietary wifi driver from MediaTek, which presumably has better perf than the opensource mt76, however that causes other issues like not being able to rev the kernel.

    In my opinion the Onion team has put more thought in the software packages for the Omega, the Linkit is more bare-bone.

    Oh and I got the i2s to work on the Omega 2 as well. I personally prefer the Omega2, it has some kinks, but I like solving problems. However only you can decide what works best for your project.

    Oh did I mention the pins on the LinkIt are standard spacing (2.54mm) ;-)



  • So for 10+ units the LinkIt is $12.50 compared with the 2+ at $9.00.

    I think for many basic users the additional cost of the LinkIt is well worth it for the plug and play features like USB host and power together with regular pin spacing.



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