Date: Tue, 02 Jun 2020 07:49:39 -0600 From: Ian Lepore <ian@freebsd.org> To: "Dr. Rolf Jansen" <freebsd@cyclaero.com> Cc: freebsd-arm@freebsd.org Subject: Re: BeagleBone AI Message-ID: <840faedfcf7c3c09a372cf566acddd8ad876ff2b.camel@freebsd.org> In-Reply-To: <3CA84BA5-FEA8-4BD8-A713-C794139170EE@cyclaero.com> References: <DCF67826-C2CA-461F-9A61-F934F6FB042A@cyclaero.com> <966c33ea1924c2cfab5d9e295a9239d134e03f8a.camel@freebsd.org> <3CA84BA5-FEA8-4BD8-A713-C794139170EE@cyclaero.com>
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On Sun, 2020-05-31 at 16:56 -0300, Dr. Rolf Jansen wrote: > > Am 31.05.2020 um 14:11 schrieb Ian Lepore <ian@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
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