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Highest priority DMA / DMA queuing bypass?

S Wade
Prodigy 120 points
Other Parts Discussed in Thread: TMS320DM6437

Hello, I’m using a dm6437 and I’m finding that some of my DMAs related to image acquisition are being delayed multiple image lines. Is there a way to have a DMA copy bypass the usual queuing process and have it happen before anything else that might be sitting in the queues? Thanks, Swade

  • 0
    TI__Genius 10440 points

    S Wade,

    Prioritization within the Switched Central Resource (SCR) is programmable for each master in the system. The VPSS, as well as the EDMAs, on the device default to having the highest priority of 0. The default priority levels of all masters can be found in section 3.6.1 of the TMS320DM6437 datasheet (http://www.ti.com/lit/gpn/tms320dm6437).  There are two priority registers that we should check as a starting point to ensure that they are still set to the highest priority and have not been changed by software after power up.

    1.) The VPSS Peripheral Control Register (PCR) should have the DMA_PRI (bits 0-3) set to the highest priority of 0. This register field defaults to this value but we should check that it has not been changed. Described in the VPFE document here: http://www.ti.com/litv/pdf/spru977d

    2.) The EDMA Queue Priority Register (QUEPRI) should also have its priorities for each transfer controller defaulted to the highest priority of 0. It should be noted that each transfer controller of the DMA has its priority set by different bits in this register. So if you have one transfer controller transferring your image while the other transfer controllers are doing less important tasks then you could lower their priorities here. This register is described in the EDMA3 Controller document here: http://www.ti.com/litv/pdf/spru987a

     It would also be a good idea to check that the other masters on the system that are listed in section 3.6.1 of the datasheet haven't had their priorities raised to a point where they would contend with a VPSS or an EDMA transfer on the device.

    Let me know if this helps,

    Jason Reeder