Serial console

[Thra11]

I've have no problems with USB enumeration and the adapter works fine with u-boot but shortly after the kernel starts the display and serial port stop working if the adapter is left plugged in. This does not happen with my handmade adapter.

I've also been experiencing the issue you describe. I believe it's also the same issue as mentioned here (in relation to RockPRO64) Interestingly, it narrows the problem down to the RX pin (although of course the suggested workaround isn't possible with the jack version, as you can't disconnect only one of the contacts: Plugging the jack in a little later in the boot sequence does work, if you only need to see later boot output). Likewise, I've also observed that other USB-serial adaptors don't cause the problem. I'd be interested to find out what exactly is going on, and whether it might be fixable.

[zaius]

I've have no problems with USB enumeration and the adapter works fine with u-boot but shortly after the kernel starts the display and serial port stop working if the adapter is left plugged in. This does not happen with my handmade adapter.

I've also been experiencing the issue you describe. I believe it's also the same issue as mentioned here (in relation to RockPRO64) Interestingly, it narrows the problem down to the RX pin (although of course the suggested workaround isn't possible with the jack version, as you can't disconnect only one of the contacts: Plugging the jack in a little later in the boot sequence does work, if you only need to see later boot output). Likewise, I've also observed that other USB-serial adaptors don't cause the problem. I'd be interested to find out what exactly is going on, and whether it might be fixable.

If having the RX pin connected is the problem, then the manufacturer of the cable should not make a difference.

One could make a cable with an inline switch that disconnects the RX pin.

Could someone please replicate this problem?  Then I can add it to the Wiki.

[Thra11]

If having the RX pin connected is the problem, then the manufacturer of the cable should not make a difference.

It depends. Different cables have different circuits with different controller chips hidden in the USB end of the cable. If e.g. the RX line needs to be held low, but some adaptors allow it to float, or produce too much noise, this could be interpreted as data by the RK3399, or might interfere with it in some other way.

I haven't seen any reference to this problem with any of Pine64's A64 boards/laptops, only the RK3399 ones (RockPro64 and Pinebook Pro).

[zaius]

If having the RX pin connected is the problem, then the manufacturer of the cable should not make a difference.

It depends. Different cables have different circuits with different controller chips hidden in the USB end of the cable. If e.g. the RX line needs to be held low, but some adaptors allow it to float, or produce too much noise, this could be interpreted as data by the RK3399, or might interfere with it in some other way.

I haven't seen any reference to this problem with any of Pine64's A64 boards/laptops, only the RK3399 ones (RockPro64 and Pinebook Pro).

Then perhaps Dan's homemade adapter works because it uses a different chip?

The Wiki reads "you can make your own if you have a serial console USB 2.0 adapter and old/ broken headphones", which would lead one to believe that there are no significant differences between serial console USB 2.0 adapters.  The one Pine64 sells is "powered by CH340 chipset".  So it seems we need to figure out which chipsets work with the RK3399.

In the meanwhile, at exactly what point is it safe to insert the Pine64 cable?