BeagleBone Black with a I2C Digital Analog Converter

[Dr. Rolf Jansen]

> Am 08.08.2018 um 14:05 schrieb Dr. Rolf Jansen <rj at obsigna.com>:
> 
>> Am 08.08.2018 um 12:45 schrieb Ian Lepore <ian at freebsd.org <mailto:ian at freebsd.org>>:
>> 
>> On Wed, 2018-08-08 at 10:59 -0300, Dr. Rolf Jansen wrote:
>>> 
>>> ...
>>> Please can somebody, check this, and perhaps give some hints in case I got something wrong? I don't have an oscilloscope, a multimeter only, can I check somehow if I specified the correct pins?
>>> 
>>> What needs to be done next? I guess, I need to write a simple device driver, don't I? Or can I use somehow the iicbb(4) – I2C generic bit-banging driver, since actually that DAC chip needs bit banging only -- repeatedly write 3 byte in row. I yes, how can I use it for my purpose?
>> 
>> At this point, i2c(8) is your friend, it lets you do i2c bus
>> transactions from the commandline without a device-specific driver for
>> each i2c device. A good starting point is a bus scan:
>> 
>>   i2c -f /dev/iic1 -s
>> 
>> If the bus is working you should see something like:
>> 
>>   Scanning I2C devices on /dev/iic1: 60
> 
> Ian, thank you very much for your response.
> 
> As a matter of fact, the source of all my doubts told in the initial post above is that yesterday after hours in a trial&error circle, I was not able to get a sensible response from the exact bus scan command which suggested:
> 
> i2c -f  /dev/iic1 -s -v
> 
> Up to now, by no means I was able to see anything else than:
> 
> dev: /dev/iic1, addr: 0x0, r/w: r, offset: 0x00, width: 8, count: 1
> Hardware may not support START/STOP scanning; trying less-reliable read method.
> 
> This START/STOP thing let me to think that I perhaps need to get attached a device driver.
> 
> I am also still in doubt, whether I really got the pinmux straight. I checked very carefully the physical connections, 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). I started to use it with 5 V, and by no means I got any response from it. After doing a full u-turn around the block – to no avail I tried all possible settings with FreeBSD 11.2, then all with Debian/Linux 9, then all with new spare DAC board – I switched the Vcc to the 3.3 V supply, and it works. Halleluja! I am back on FreeBSD 12-CURRENT, and I can live with 3.3 V, since I need to pass the DAC output through a scaling OpAmp anyway in order to have 0 ... 10 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.

Best regards

Rolf