SPI Minimum Speed

Products Support DragonBoard410c
#1

I am unable to get the SPI speed to go below 1Mhz on Linaro Linux 4.4.

I have found using spidev_test.c that any speed below 1Mhz causes the SPI speed to default to 1Mhz (verified with a scope and consistent with this post: [OE] Mix/Max SPI clock ranges?)

Is there any way to reduce the clock speed of SPI on the DB410c? Is there perhaps a clock divider register I can set?

#2

I also tried to reduce SPI clock speed but with no result. Is there any possibility to work with SPI in speed lower than 1MHz?

#3

You need to apply this kernel patch: https://patchwork.kernel.org/patch/10692881/

#4

F(100000, P_XO, 16, 2, 24),
what do this numbers mean?

#5

F(target-freq, clock-source, Predivider, Multiplier, Divider),

so that target-freq = clock-source-freq / P * M / D

with clock-source freq = P_XO = 19200000 Hz

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#6

I need to get speeds from 1, 5, 10 ,20,25,50 kHz

#7

I need to get speeds from 1, 5, 10 ,20,25,50 kHz

So maybe add the following line for 50Khz:
F(50000, P_XO, 16, 1, 24),

For 25:
F(50000, P_XO, 16, 1, 48),

I let you calculate the other. Note that I’m not sure about the limit of the predivider/divider.

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#8

thanks. I wiil try to calculate