Thank you very much, this is interesting information! MOSI is indeed one of the bootstapping pins, called CHIP_MODE_2. However, the MT7688 only has 4 modes, which are defined by CHIP_MODE_1 and CHIP_MODE_0 alone - see page 31 of the MT7688 Datasheet. The datasheet does specify that CHIP_MODE_2 should be 0, but it does not say what CHIP_MODE_2==1 would mean. Unlike the other bootstrap pins, which are documented to have pullups or pulldowns inside the Omega2(S), I never found an indication that CHIP_MODE_2 does have a pulldown. The Omega2S datasheet just says that MOSI can't be used as a GPIO (obviously, as it is used by the SPI flash), but nothing about pullup/downs. So my working assumption till now was that CHIP_MODE_2 is not actually sampled at SoC boot - which turns out to be wrong! Apparently, it is important that CHIP_MODE_2/MOSI is 0 at boot, so I guess there must be a weak pulldown somewhere, be it in the Omega2(S) or in the SoC itself. And in consequence, as you found out, that pin must not have external pullups... So I just updated my annotated Omega2 + Omega2S pinouts accordingly. @Lazar-Demin: maybe it would make sense to mark the MOSI pin red in the datasheet too? And btw., the MT7688 datasheet links you have in the onion docs no longer work - I found this one as a replacement.