Date: Tue, 2 Jun 2020 12:22:51 -0300 From: "Dr. Rolf Jansen" <freebsd@cyclaero.com> To: Oskar Holmlund <oskar.holmlund@yahoo.com> Cc: Ian Lepore <ian@freebsd.org>, freebsd-arm@freebsd.org Subject: Re: BeagleBone AI Message-ID: <72C6B827-3F3E-4CB2-8987-C926602F755D@cyclaero.com> In-Reply-To: <479317334.2616392.1591110518765@mail.yahoo.com> References: <DCF67826-C2CA-461F-9A61-F934F6FB042A@cyclaero.com> <966c33ea1924c2cfab5d9e295a9239d134e03f8a.camel@freebsd.org> <3CA84BA5-FEA8-4BD8-A713-C794139170EE@cyclaero.com> <840faedfcf7c3c09a372cf566acddd8ad876ff2b.camel@freebsd.org> <5299B3F7-1C95-4769-9701-F13699FE355C@cyclaero.com> <479317334.2616392.1591110518765@mail.yahoo.com>
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> Am 02.06.2020 um 12:08 schrieb Oskar Holmlund = <oskar.holmlund@yahoo.com>: >> Den tisdag 2 juni 2020 16:56:02 CEST, Dr. Rolf Jansen = <freebsd@cyclaero.com> skrev:=20 >>> Am 02.06.2020 um 10:49 schrieb Ian Lepore <ian@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@freebsd.org>: >>>>>=20 >>>>> On Fri, 2020-05-29 at 23:21 -0300, Dr. Rolf Jansen wrote: >>>>>> ... >>>>>>=20 >>>>>> First Question: >>>>>>=20 >>>>>> What modern SBC with more than 1 I=C2=B2C bus and which can run >>>>>> FreeBSD 13++ would you suggest? >>>>>>=20 >>>>>> ... >>>>>>=20 >>>>>> Two more Questions: >>>>>>=20 >>>>>> Is it reasonable to assume that FreeBSD would run on a BBAI in >>>>>> the future, let=C2=B4s say in 2 to 3 years? >>>>>>=20 >>>>>> Perhaps I could help porting FreeBSD to a BBAI. What would be the >>>>>> general steps? >>>>>>=20 >>>>>>=20 >>>>>> Many thanks in advance for any suggestions, advices and >>>>>> clarifications. >>>>>>=20 >>>>>> Best regards >>>>>>=20 >>>>>> Rolf >>>>>=20 >>>>> BTW, if you need drivers for any new i2c devices just let me know >>>>> and >>>>> I'll see what I can do. >>>>=20 >>>> 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=C2=B4= t >>>> need exactly a driver for new I=C2=B2C devices. However, I am far = away >>>> from being a perfect I=C2=B2C 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. >>>>=20 >>>>> 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. >>>>=20 >>>> Does this =E2=80=9Eover clocking=E2=80=9C 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 :-) >>>>=20 >>>> Best regards >>>>=20 >>>> Rolf >>>=20 >>> 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. >>>=20 >>> 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. >>>=20 >>> -- Ian >>=20 >> 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 I=C2=B2= C devices, we will perhaps run into some timing issues, and then I = probably want to revisit changing the clock frequency again. >>=20 >> Expect no more than 1MHz >> = https://svnweb.freebsd.org/base/head/sys/arm/ti/ti_i2c.c?revision=3D355727= &view=3Dmarkup >> Line 127+ >>=20 >> //Oskar Ah, OK, that explains the finding. So perhaps the bus is really working = at 1 MHz. Thank you very much for the hint. Best regards Rolf=
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