(Zephyr / NCS) Increase SPI buffer length

[zciwor]

I'm using the Zephyr provided WS2812 LED driver (SPI). I am noticing some strange behavior when my chain-length property is greater than 10.

I connected a digital logic analyzer to take a closer look and discovered that I am being limited by the SPI's TX buffer length. It is clear that after 255 bytes, my data line is interrupted for ~22us before writing the rest of my buffer. I have attached a screenshot. 

The WS2812 LED driver is very time sensitive so this interruption is ruining my LED control. Is there a way to increase the SPI TX buffer length in Zephyr to greater than 255? My LED chain-length is 13 so I will need to increase it to at least 312 (24 bytes per LED * 13 LEDs). 

[Kenneth]

The nRF52832 only have 8-bit (255bytes) max SPIM transfer length, in your case you need minimum 10-bit (See MAXCNT bit length):
https://infocenter.nordicsemi.com/topic/struct_nrf52/struct/nrf52.html