On Thu, Oct 20, 2016 at 8:56 PM, George Rung <rickyr...@gmail.com> wrote:
> > I am able to get *SPI0 *working on the BeagleBone Black by using only > *config-pin* commands: > > config-pin P9_17 spi > config-pin P9_18 spi > config-pin P9_21 spi > config-pin P9_22 spi > > Then writing to */dev/spidev1.0 *causes data to come out the pins P9_18 > (data) and P9_22 (clock). > > Note that searching for how to enable SPI on the BeagleBone returns > tutorials that all involve *"device trees"* or a *"cape manager"*. None > of this was necessary for me to get SPI working. I assume they used to be > required at some point in the past. I simply set the pins to SPI and it > works. > Actually, device tree file(s) were involved, you just did not realize it. By using config-pin, you're using one of the universal IO device tree overlays. > > Now I'd like to change some SPI settings, like the clock rate. It seems > the hardware has a frequency divider that can be set to change the SPI > clock rate. What is the clock rate by default? How can I change it? > Ideally I'd like to change it by command with the BeagleBone running, > hopefully no recompiling or rebooting required every time I make a change. > > How should I go about this? > > Note that I'm running the image > *"bone-debian-8.6-iot-armhf-2016-10-16-4gb.img.xz"* found here: > > <http://goog_839341451> > https://rcn-ee.com/rootfs/bb.org/testing/2016-10-16/iot/ > So, I do not really know much about the SPI hardware per se. However, I do know that if you check an overlay file for SPI, say : https://github.com/beagleboard/bb.org-overlays/blob/master/src/arm/BB-SPIDEV0-00A0.dts#L63 Look at the highlighted line. If you're wanting to raise the frequency, there is is. But except if you're wanting to use a universal IO overlay, which I completely understand. You'll have to edit the file that is preloaded at boot, *or* the overlay file that is loaded when you invoke the config-pin script. As far as the clock, and divider . . . Well as I recall the clock is 48Mhz, which means if the frequency is 16Mhz, the divider is 3x. Anyway, as I said I really do not know the SPI hardware well. SO take what I say with a grain of salt. As what I'm saying concerning the clock and divider is going by memory. Where I've never used the hardware, and my memory is sometimes less than perfect. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CALHSORrNenkwJoD3LOZKL9cYcPiVTNoO_bt%2BeXR_zD%3DYCJgcYA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
