Is there an example code of the SPI interface using MRAA on the Joule?
I see one example located here but it is not specific to a platform https://github.com/intel-iot-devkit/mraa/blob/master/examples/spi_max7219.c https://github.com/intel-iot-devkit/mraa/blob/master/examples/spi_max7219.c
Thank you for your interest in the Joule platform.
I haven't tested these examples with Joule, however, MRAA supports many X86 platforms including the Intel Joule as it is stated here https://github.com/intel-iot-devkit/mraa. With that in mind, I believe it should work with the Joule board so I would suggest you to give a try. I would also suggest you to check this link http://iotdk.intel.com/docs/master/mraa/grossetete.html.
Given the example is in the official MRAA Github page, you can also contact them if you encounter any issue.