BeagleBone Black with a I2C Digital Analog Converter

[Dr. Rolf Jansen]

> Am 11.08.2018 um 17:42 schrieb Ian Lepore <ian at freebsd.org>:
> 
> On Sat, 2018-08-11 at 17:30 -0300, Dr. Rolf Jansen wrote:
>>> 
>>> ...
>>> , anyway I am
>>> stuck at this point.
>> 
>> I got it working.
>> 
>> 1.) The specification of the DAC board which I attached to my BBB was
>> wrong in regards to the acceptable Vcc voltage range (2.7 to 5.5 V).
>> ... 
>> 
>> 2. There is still something wrong with my overlay. I need to hack in
>> the same I2C1 changes into the main DT, and then the bus scan by i2c
>> -f  /dev/iic1 -s gives me the expected output. For my present project
>> this is a minor issue, though. My best guess here is, that there is a
>> problem with the reference of the I2C1 node to the proposed pinmux
>> node.
>> 
>> On Debian/Linux the very overlay does work.
>> 
> 
> Ah.  The board probably does support 2.7-5.5v, but if the i2c bus has
> pullups that only pull the lines up to 3.3v, that may be too close to
> the VIH transition levels for the DAC chip running at 5v. Even if it's
> within the VIH range, if the pulls aren't strong enough the clock
> signal may not rise above the 5v VIH fast enough for reliable comms.

I was too happy too soon.

Now, I updated my system to the 12 snapshot from yesterday, which turned it from 12-CURRENT to 12-ALPHA1, and with that one, the issue number 2 above turned from a minor issue to a major problem, in order not to say a whole new barrier is now blocking all my further efforts. It seems that in 12-ALPHA1 the DTB is statically compiled into the kernel, and now I cannot simply hack-in anymore some nodes which don't work by the way of overlays

OK, in the moment I may switch back to 12-CURRENT, however, I am elaborating this project with 12 now, so I won't have any headaches in the future. Now I am stuck again. Please may I ask for an advice?

May I expect that pinmuxing will work in a not too distant future with overlays?

Am I really supposed to build a custom kernel, only for getting 2 pins straight? Building a kernel takes forever on the BBB.

Shall, I forget 12 and stay with 11 for the next years?

BTW: The startup script /etc/rc.d/ntpd got a flaw. The -p option must be removed from the cmdargs.

Best regards

Rolf