Is it possible to have the SPI clock run at 3.5MHz

[SGen]

Hi,

I am doing a project to interface a customized multi-channel ADC with SPI. The ADC only samples data at some set frequencies by writing the right number in registers. So the required SPI clock speed is different from those given in the bcm2835 library. Setting BCM2835_SPI_CLOCK_DIVIDER_128 gives 3.15M on pi 3 and BCM2835_SPI_CLOCK_DIVIDER_64 give 6.25M. What should I do if I need a non-standard clock rate such as 3.5M? Thank you for any help.

[Mike McCauley]

Hi,

Are you sure that you have to use that SPI frequency? Most such SPI devices
will tolerate a wide range of SPI frequencies. Check the specs on your device.

Cheers.

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Mike McCauley VK4AMM mi...@airspayce.com
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Phone +61 7 5598-7474

[Arjan van Vught]

Op 27 mrt. 2020, om 23:53 heeft SGen <suryg...@gmail.com> het volgende geschreven:

Hi,

I am doing a project to interface a customized multi-channel ADC with SPI. The ADC only samples data at some set frequencies by writing the right number in registers. So the required SPI clock speed is different from those given in the bcm2835 library. Setting BCM2835_SPI_CLOCK_DIVIDER_128 gives 3.15M on pi 3 and BCM2835_SPI_CLOCK_DIVIDER_64 give 6.25M. What should I do if I need a non-standard clock rate such as 3.5M?

Please see bcm2835_spi_set_speed_hz()

http://www.airspayce.com/mikem/bcm2835/group__spi.html#gad58ade25f8eaaacd4d9249f51af4d1f3

- Arjan

Thank you for any help.

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[Geng Jinghui]

Hi Mike,

I checked the datasheet. It gives a table of the ADC sampling rate per channel and the corresponding buffer bias and mux bias for the registers. Do you mean that the ADC should follow the SPI speed and each set of register variables is able to give different sampling rates in a range? Are there any devices that I can use to test the ADC? Than you.

Best,

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[Geng Jinghui]

Hi Arjan,

Thank you. Do you mean it's impossible? 

Best,

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[Arjan van Vught]

Op 31 mrt. 2020, om 02:33 heeft Geng Jinghui <suryg...@gmail.com> het volgende geschreven:

Hi Arjan,

Thank you. Do you mean it's impossible? 

You can set any frequency you would like between 4KHz and 125MHz

- Arjan

https://github.com/vanvught/rpidmx512

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[Geng Jinghui]

Thank you, Arjan! I think I got it. 

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