NRF9160 zephyr SPI - CS stay low too long

Question

Hi,
I'm working on nRF9160 with Zephyr (SDK 1.7.1) and one SPI device. I analyze CS signal with correlation to SPI SCK. Is that normal that CS signal stays low much longer than SCK signal?

For example:
SPI SCK = 2 MHz:

CS goes low ~8us before SCK and goes high ~21 us after the end, while communication takes 12us.

SPI SCK = 8 MHz:

CS goes low ~7us before SCK and goes high ~7us after SCK, while communication takes 3us.

When I working with time sensitive SPI devices - these delays matter a lot. Is there a chance to reduce them?

&spi0 {
	compatible = "nordic,nrf-spim";
	status = "okay";
	sck-pin = <21>;
	mosi-pin = <22>;
	miso-pin = <23>;
	cs-gpios = <&gpio0 24 GPIO_ACTIVE_LOW>;
};

Of course - I set CS gpio delay to 0.

Saleh · Answer

Hi 
 
 It seems the problem is coming from Zephyr side, a similar question was asked before and results show that this annoying delay is the normal behavior of the current Zephyr's version. 
 https://devzone.nordicsemi.com/f/nordic-q-a/81966/slow-spi-performance-with-zephyr

NRF9160 zephyr SPI - CS stay low too long

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