It has taken me a considerable amount of time to prove that the SPI interface can be made to work with cortex M4 on the UDOO Neo. To demonstrate the speed of SPI I chose to interface with a SSD1306 OLED which can be driven at a clock speed of 8Mhz. Which theoretically should allow a complete RAM buffer to transmitted to the SSD1306 in a very short time period hence offering fast screen updates. To control the speed of screen updates I hooked up an old potentiometer to the ADC input. By varying the potentiometer we control the rate of updates from slow to fast as shown in the video.
The SPI interface is configured for Master mode using interrupts for data transmission resulting in acceptable performance. To reduce interrupt latency further, DMA could be used to transmit the whole RAM buffer in one go.
I chose to use ECSPI 2 (normally allocated to the A9 side) and not ECSPI 5 because after reviewing the schematics I think there is a hardware bug with ECSPI 5 as the ECSPI5_SCLK line is shared with Red on board LED (see SPI3_CLK on J6 connector).
This is a C application developed using i.mx6sx FreeRTOS SDK. The graphics rendering code was converted from the Haricord example by hwiguna.