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Can the AM1808 PRU be programmed for I2C Ports?

Johnny Lau
Intellectual 2465 points
Other Parts Discussed in Thread: AM1808

We have a custome that is interested in Digital Power but must independently control up to 72 PoLs on their board.  They believe they need more bandwidth than achievable on a single PMBus.  We are thinking of using the AM1808 to interface to several PMBusses, say 8 or 10.  The AM1808 has two native I2C busses.  Can more be added through the PRU.  If so how many do you estimate?

PMBus is using the I2C protocol for reference

  • 0
    TI__Genius 15910 points

    Hi Johnny,

    We have not seen an I2C implementation on the PRU yet, but it should be feasible.  This forum post includes general advice about performing feasibility assessments on the PRU.

    Here are also some things to consider about a PRU I2C implementation:

    1.   If considering a GPIO bit-banging approach, realize that the PRU's dedicated I/Os are unidirectional.  There are separate and independent PRU GPI and GPO pins.  Two work-arounds are 1) connect the two I/O’s in external hardware and add a buffer to the GPO pin, or 2) use the device’s generic GPIOs.  Note there are additional latencies (between 15 – 20 cycles) when accessing the generic GPIOs.

    2.  When assessing the feasibility of multiple I2C's, keep in mind that the PRU is single-threaded and is not preemptive by system events.  Instead, it must poll to detect interrupts.  Therefore, a potential challenge with multiple I2C’s may be scheduling tasks.

    3.  When accessing the performance capability or rates feasible, note that on AM18x the tightest loop to toggle a PRU R30 GPO pin consumes 3 cycles.  The number of PRU cycles the I2C algorithm requires will impact the achievable speeds. 

    Regards,

    Melissa

  • 0 in reply to melissaw
    TI__Genius 15910 points

    The link to the forum post I mentioned is:

    http://e2e.ti.com/support/dsp/sitara_arm174_microprocessors/f/47/p/104742/404221.aspx#404221

    Regards,

    Melissa