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PS SPI frequency

Former Member

Hello guys,
I have been working on zedboard since past few months.
I have a doubt regarding the SPI frequency and baud rate. As mentioned in the section B.30 of zynq 7000 Technical reference manual, there are 7 baud rate divisors.
My doubt is how to achieve any desired frequency ?
I have my spi code, i ran the code onto zynq ps section.
I connected oscilloscope to SCLK and ground and found out that the frequency was something 300khz, which seemed to be very incorrect(baud rate divisor was 4) as the clock frequency for SPI master has to be in the range 0 to 50Khz.
Can anybody tell how to precisely obtain any frequency and how to cross verify it whether it is correct or not ?
Is there any process to set frequency except the baud rate thing ?
Kindly suggest me over this.
Thanks.

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  • 0

    Hello,

     

    Not sure what you mean by 'baud rate'.

     

    The SPI clock input is set in the Zynq Processing System hardware. If you open your Zynq Processing System IP in your block diagram and click on 'Clock Configuration' and expand 'IO Peripheral Clocks' you should see the SPI clock. The default is 166.66 MHz. You can leave that as the default (It must be at least 111 MHz).

     

    Then, in your SPI driver code, you can set the clock divider. If you look in the xspips example code you will see a call to a function XSpiPS_SetClkPrescaler. You can set the divisor for the 166.66 MHz input clock there. So, using the definition XSPIPS_CLK_PRESCALE_256 , will get you an SPI clock of around 651 KHz as an example.

     

    -Gary

  • 0 in reply to Former Member

    Thanks for the reply, Gary.
    That was very clear. I was able to successfully test it.
    But I have one more doubt regarding the maximum data transfer rate when zynq 7000 acts as a master.
    I have selected the default SPI frequency from the Zynq Processing System hardware as 166.66Mhz. And I am using a prescale of XSPIPS_CLK_PRESCALE_8 and XSPIPS_CLK_PRESCALE_16. I am loop testing this i.e I have connected MOSI to MISO.
    But I still manage to get only 6Mbps data transfer rate.
    Is there any way I could increase the data rate ?I also tried making the default frequency to 200Mhz, but there was not much change. Is there a way I could increase the datarate ?
    And what is the maximum datarate I can acheive using SPI ?
    Thanks for all the efforts.

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