12-05-2019, 08:35 AM
(12-05-2019, 04:07 AM)danielt Wrote:(12-05-2019, 03:06 AM)Solra Bizna Wrote: The wiki does mention that some of these cables render the PBP unbootable, but I didn't see any previous mention of this on the forums. I assume that previous discussion of this problem has happened in other media.
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This cable is still useful for basic boot troubleshooting (of the "did my kernel boot at all?" variety), but something is clearly very, very wrong.
This sounds exactly like my experience with the official pine64 cable. It has been discussed on the forum but not for some time (so don't worry). If you are interested one of the older threads is here: https://forum.pine64.org/showthread.php?tid=7746
I'm afraid I gave up completely on the official cable and soldered together a cable to connect one of my existing UART adapters to the PBP. This works fine and enabled me to do plenty of interesting hacking. Having said that I'm still a bit disappointed that the official cable is non-functional for so many people.
Actually thanks for reminding me about this...
I had a theory about what might be going wrong but it seemed so unbelievable that I didn't check it out. However given I still can't think of any other way for an UART adapter that is sending no characters to crash the Pinebook I broke out my multimeter.
It looks like I was right... although I'd be grateful if someone else can confirm it since I'm still rather in shock...
The official adapter is using 5v TTL logic when it should be using 3.3v TTL logic. In other words it appears to be over-volting the UART circuit on the board and causes enough electrical havoc to (eventually) crash the machine.
My advice would be to IMMEDIATELY STOP USING YOUR ADAPTER FOR ANY PURPOSE until you have measured the voltage between the middle two rings on the adapter.
(sorry for shouting but there is a risk of damage from this sort of thing).
I have the original serial console cable for the Pinebook (1080p) and, in response to an earlier query about serial interface, I measured my own quiescent voltages on the 3.5mm 4-pole jack it was terminated in ... and yes it was 5v.
Not sure if there was any internal impedance that might reduce the final voltage to the Pinebook when "under load" but it did seem odd.
(never actually used the cable with my Pinebook 1080p or with the Pinebook Pro - the latter because it required the case to be opened and the terminal/sound switch toggled - I'd rather not break anything just now)