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Enabling DMA for McBSP2 for Audio rendering on OMAP3530

jack9310
Intellectual 280 points
Other Parts Discussed in Thread: TPS65950

Hi All,

I am trying to use McBSP2 for rendering audio samples to the TPS65950 audio codec module. I am trying to enable DMA for that.

What is the size of transmit buffer in McBSP2? Spec says that it has 4Kbytes audio buffer and 1Kbytes Transmit buffer. 

I need to configure the Transmit threshold value in MCBSPLP_THRSH2 register for a hardware synchronized DMA transfer. Spec says that  as long as the XB(Transmit Buffer) free locations level is above or equal to the THRSH2_REG value + 1, the DMA request will be asserted. After transferring the configured THRSH2_REG value + 1 number of words, the transmit DMA request will be de-asserted and reasserted as soon as the conditions are met again.

Assuming Transmit buffer is 4Kbytes , Planning to set Threshold Value as 256 Words(1Kbytes).  When the free locations in 4Kbytes buffer goes beyond 1Kbytes DMA is automatically triggered. 

 

Expecting Help on this

 

Regards

Jack

 

  • 0
    Prodigy 60 points

    Hi.

    Whatever spec says, actually  you must consider  XB as a global entity. Thus, the whole size of  the XB = (1024*32) + (256*32) = 5Kbytes. This means that you have two FIFO that act as one.

    Imagine you're programming an xthreshold interrupt. When you set a XTHRESHOLD_SIZE, it doesn't  matter the size, because the interrupt will trigger whatever happens as there are 0x500 free locations since the first moment.

    I think you first must manage with simple McBSP interrupts instead of DMA programming, let that staff for a next step.