BeagleBone AI

[Dr. Rolf Jansen]

> Am 02.06.2020 um 10:49 schrieb Ian Lepore <ian at freebsd.org>:
> 
> On Sun, 2020-05-31 at 16:56 -0300, Dr. Rolf Jansen wrote:
>>> Am 31.05.2020 um 14:11 schrieb Ian Lepore <ian at freebsd.org>:
>>> 
>>> On Fri, 2020-05-29 at 23:21 -0300, Dr. Rolf Jansen wrote:
>>>> ...
>>>> 
>>>> First Question:
>>>> 
>>>> What modern SBC with more than 1 I²C bus and which can run
>>>> FreeBSD 13++ would you suggest?
>>>> 
>>>> ...
>>>> 
>>>> Two more Questions:
>>>> 
>>>> Is it reasonable to assume that FreeBSD would run on a BBAI in
>>>> the future, let´s say in 2 to 3 years?
>>>> 
>>>> Perhaps I could help porting FreeBSD to a BBAI. What would be the
>>>> general steps?
>>>> 
>>>> 
>>>> Many thanks in advance for any suggestions, advices and
>>>> clarifications.
>>>> 
>>>> Best regards
>>>> 
>>>> Rolf
>>> 
>>> BTW, if you need drivers for any new i2c devices just let me know
>>> and
>>> I'll see what I can do.
>> 
>> I am pretty comfortable with register level programming, and so far I
>> came away with ioctl() calls for what I needed. So perhaps I won´t
>> need exactly a driver for new I²C devices. However, I am far away
>> from being a perfect I²C expert, specially when it comes to timing
>> and the best sequence of addressing different devices on the bus.
>> Perhaps, I may ask some questions when I run into problems.
>> 
>>> Also, in my experience you can often get away with running an i2c
>>> bus
>>> faster than 400khz if you need more bandwidth.  I've never seen any
>>> modern chip fail to work at 800khz, and most seem to work fine up
>>> to
>>> about 1mhz; above that they become pretty unreliable.
>> 
>> Does this „over clocking“ work for the ARM boards as well? I just set
>> the clock-frequency in the dts-overlay which activates I2C1 of the
>> BBB from 400000 to 800000. The bus seems to work as usual, however, I
>> did not yet come to check its speed. How again would I do that?
>> Probably there are many more questions to come :-)
>> 
>> Best regards
>> 
>> Rolf
> 
> I suspect it works on some boards and maybe won't work on others.  Some
> SOCs have very flexible clock settings in their i2c controllers, a few
> just allow choosing between fixed low and high speeds.
> 
> For experimenting, there is a sysctl dev.iicbus.#.frequency that you
> can change on the fly (it will override any value from the dts).  The
> value is the frequency in hz.
> 
> -- Ian

Thank you very much for your response. I checked the sysctl setting, and the system accepts the values. The bus works at 800000, however, I can set it as high as 10000000 (10 MHz) and it is still working. Perhaps, there is some sort of internal validation before the frequency value is actually applied to the HW. In the moment this is more a matter of curiosity than an actual need. Once we equipped the bus with all I²C devices, we will perhaps run into some timing issues, and then I probably want to revisit changing the clock frequency again.

Best reagrds

Rolf