SPI delays and overhead
 

Details :

Dear Experts

I am using ARM board (GESBC 9260) and it is using the AT91SAM9260 processor . I am currently working on data

acquisition through SPI . I am using atmel_ spi (master controller driver ) and spidev (usermode driver ) kernel 2.6.30.

kernel Information . I used the patch at www.linux4sam.org. for creating the uImage and the drivers for the SPI are standard drivers , spidev.c(usermode driver ), atmel_spi.c (mastercontroller driver) and spi.c.



All is working fine but there is this problem of delay between chip select deactivates and activates again is around :
a) for ioctl calls : around 100 microseconds

b) for read /write functions call - around 150-200 microseconds and a variable delay



I understood that the SPI chip select is being handled by the GPIO pins but still the GPIO's are targetting specific chip select pins only. What I am totally unable to understand what is causing this much of delay. (The master clock is taking only 15 microseconds to generate 64 clocks )and then chip select becomes high and remains high for around 100 microseconds . I wonder what is the processor doing ?? I would request you experts to look into the matter and please advice accordingly....

Thanks Amit