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AM335x PRU direct access to SPI

Michael Haberler
Prodigy 170 points
Other Parts Discussed in Thread: ADS8688

or is bit-banging the only way to achieve this?

thanks in advance,

- Michael

  • 0
    Intellectual 280 points

    I am also very interested in this - any examples would be much appreciated.

  • 0
    TI__Mastermind 44306 points

    PRUs do have access to all system peripherals. This is not as fast as the PRU-ICSS integrated peripherals access but it works and we have used SPI with PRU before.

    Regards.

  • 0 in reply to Frank Walzer
    Prodigy 170 points

    Hi Frank,

    thanks for the hint.

    I assume you used memory-mapped I/O to talk the SPI logic, just that memory access comes from the PRU, not from the main CPU?

    best regards

    Michael

  • 0 in reply to Frank Walzer
    Prodigy 25 points

    Hallo Frank,

    it's really motivating to hear that a SPI-Module is enabled using PRU. I've been working on it for a long while but without results :/. Do U  have any sample code ?  

     

    thanks.

  • 0 in reply to bessem baccouche
    Prodigy 30 points

    Hello,

    I need to complete a fast ADC / DAC with some numeric matrix calculation. I thought about using a BBB, and the PRUs seemed to be a very interesting point. The numeric part could be done using Xenomai.

    You said that the use of SPI with the PRUs is possible. So can I use SPI ADC / DAC with the PRU ?

    Could you be more precise on how to do ? Write SPI drivers for the PRU ? 

    If I was not clear enough, tell me :)

    Thank you very much

  • 0 in reply to Alexis Martin
    TI__Mastermind 18130 points

    Hi Alexis,

    The PRU core(s) have direct access to system peripherals such as the SPI port, so there is nothing preventing you from accessing an ADC/DAC assuming it can keep up from a MIPS perspective.

    As the PRU does not run the Linux kernel the kernel drivers are not available to the PRU cores; however, if you were to write some code for the PRU to handle the SPI port (i.e., a "driver" as you mentioned) then you could indeed service a DAC/ADC.

  • 0 in reply to TimHarron
    Prodigy 30 points

    Hi Tim, thanks for your answer.

     

    What do you mean by "assuming it can keep up from a MIPS perspective" ?

    In which documentation can I find most useful information how to write the code to use ADC/DAC for the PRU via SPI port ?

  • 0 in reply to Alexis Martin
    TI__Mastermind 18130 points

    Alexis,

    Alexis Martin said:
    What do you mean by "assuming it can keep up from a MIPS perspective" ?
    As long as you are not trying to get the PRU to run more code than it can handle then there's no issue.

    We don't have documentation discussing how to write a SPI driver on the PRU. There is a C compiler available in the CCSv6 App Center (note this is still a Beta product) which supports the full C/C++ language as well as the PRU Assembly instruction set. If C is your language of choice you can use this to write up your driver.

    The PRU has access to the full memory map so it can access the SPI port directly via something as simple as a pointer. The only public information we have today on the PRU is covered in this github project, specifically the Reference Guide. Bear in mind that there are sections covering Assembly using the PASM utility which TI is not updating or supporting; however, it does cover the PRU hardware pretty well so this should be useful.

    Additionally you can refer to the AM335x TRM for information on how the SPI port functions.

  • 0 in reply to TimHarron
    Prodigy 30 points

    Can the PRU access to all ARM register? I tried with a GPIO register address (0x4804c0194 for example, see this link ) and modify a value of a bit in a register, display it by shifting out the register loaded after the modification.

    But when I try to modify SPI register it doesn't work. Here is my code, I visualize the value of r4 using the PRU shift out register. 

    // Enable OCP master port

    LBCO r0, CONST_PRUCFG, 4, 4

    CLR r0, r0, 4 // Clear SYSCFG[STANDBY_INIT] to enable OCP master port

    SBCO r0, CONST_PRUCFG, 4, 4

    MOV r1, 0x4803012C // address of SPI_CONF_CH0 register

    LBBO r2, r1, 0, 4 // Load MCSPI_CH0CONF Register (for SPI0)

    //SPICLK polarity
    //0h = SPICLK is held high during the active state 1h = SPICLK is held low during the active state 

    SET r2.t1

    SBBO r2, r1, 0, 4 // copy to  MCSPI_CH0CONF Register (for SPI0)

    LBBO r4, r1, 0, 4 // and I get 0x00000000

    Is it at least possible to make SPI working with this method, by modifying bits into registers ? Am I missing something obvious? I tried with a SPI0 disabled with device tree and SPI1 enabled with device tree and I have the same results.

    I don't want to use the kernel space and SPI driver in C. Is there an other way to do it ? Like I said in previous post "write" a SPI "driver" in assembler could be quite complicated, right?   

    Thanks a lot!

  • 0 in reply to Alexis Martin
    Prodigy 200 points
    Alexis,

    Did you solve this?
    I am doing the same thing -- trying to write to the SPI peripheral from within the PRU. I'm using the C compiler, but the method is essentially the same.
    I know the general method works, because I can successfully write to a PWM peripheral.

    I'm not having any luck with the SPI port, though -- it doesn't seem to respond.
  • 0 in reply to Damon Kelly10
    Prodigy 10 points
    Has anyone managed to solve and/or document this yet? I'm also attempting this via the C compiler but not really getting anywhere.
  • 0 in reply to Alexis Martin
    Prodigy 140 points
    Can You send the sample code to access the PRU via SPI .I have an ADC(ADS8688).I have to send the sampled data via SPI to PRU.