Hello Guys, I'm new at programming the BBB and to Linux in general, so I'm trying to figure out what's happening when I'm setting up a SPI-connection.
I have set up a SPI-connection, using a Device Tree Overlay, and I'm now running spidev_test.c <https://www.kernel.org/doc/Documentation/spi/spidev_test.c> to test the connection. For the application I'm making, I need a quite specific frequency. So when I run spidev_test and measure the frequency of the bits shiftet out, I don't get the expected frequency. <https://lh3.googleusercontent.com/-51vFiUpWoX4/VY04yMt1RfI/AAAAAAAAAJc/Lbg4QOm8y8s/s1600/BBB%2Btransmit%2B0xAA%2B%2540%2B4MHz%2B-%2Bedit.png> I'm sending a SPI-packet containing 0xAA, and in spidev_test I've modified the "*spi_ioc_transfer.speed_hz*" to 4000000 (4MHz). But I'm measuring a data transfer frequency of 2,98MHz. I'm seeing the same result with other speeds as well, deviations are usually around 25-33%. *How come the measured speed doesn't match the assigned speed?* *How is the speed assigned in "speed_hz" defined?* *How precise should I expect the frequency to be?* Thank you :) -- 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. For more options, visit https://groups.google.com/d/optout.
