Dual serial ports on RPI2, is it so?

FTDI

itself

I have a hunch that it could be power handling. With me it's only the one connected to the APC UPS that gives the most problems. Swapping around adapters (I have three bought at the same time) doen't make any difference the UPS is always the less stable.

A Pi is a Pi, swap a pair of boards between the stable and unstable groups? If the problem moves it's Pi board problem if it doesn't it's the adapter or something to do with how the Pi is being used.

I think there is some particular combination of handshake line setup and data stream that pushes the required power just that little bit too much and the chip crashes. This clears the "fault" state so it instantly reconnects.

Not here but mine aren't connected to a Pi but a HP Micro Server and the APC serial connection is not quite standard. So perhaps I don't have the right conditions to keep the chip crashed only to crash it.

I have not seen a distro which sets up the BCM2835 i/o to drive both UARTs, even though the function exists in the i/o core.

You could use a USB to serial adaptor.

Another option would be an SPI or I2C UART, but you would need to knock up a driver for it I suspect.

That's what I'm doing. Started out with PL2303TA-based units. Out of four (on four RPI2s) two worked fine and two locked up routinely, usually within 24-48 hours. Substituting FTDI-based adapters has (up to 4 days) solved the problem with the two pl2303 units that were locking up.

It's looking as if the problem isn't with the PL2303, but rather with the particular RPI2 it's plugged into. The offending RPI2s both use USB 3 flash drives for outboard storage, the two RPI2s which support the PL2303s use either a USB 2 hard drive or no external storage. Very difficult to figure why that might make a difference, but so far that's the experience.

It should be emphasized that this is with FreeBSD-11, not Raspian, but both are open source and likely use similar uplcom drivers.

Thanks for reading,

bob prohaska

One issue with USB to serial adaptors is there are a lot of poor Chinese fakes of the pl2303 and FTDI chips out there, and they do the sort of thing you describe. Make sure you buy from a trustworthy source.