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DM814x USB MUSB CPPI DMA issue?

Daniel70334
Expert 1745 points

Hi,

I've been looking at the USB serial gadget on DM814x. I had to insert a schedule_timeout() in the txdma_completion_work() loop in board-support/linux-2.6.37-psp04.04.00.01/drivers/usb/musb/cppi41_dma.c, as suggested in http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/p/230498/842210.aspx. Even so, I see that the MUSB_TXCSR_FIFONOTEMPTY bit never goes away. Specifically, I see:

  • The first packet gets sent by the PSP itself, by DMA transparent mode from acm_cdc_notify() in drivers/usb/gadget/f_acm.c, into the DMA channel for EP1.
  • The txdma_completion_work() loop shows that the EP1 fifo is never emptied - FIFONOTEMPTY is always set in TXCSR, and never goes away
  • When my application writes to the ttyGS0, that data goes to the DMA channel for EP0, in generic RNDIS mode.
  • The txdma_completion_work() loop shows that the EP0 fifo gets emptied.  I.e., the FIFONOTEMPTY bit gets set, then goes away, as expected.

I don't see mention of this in the known deficiencies in the EZSDK 5_05_02_00 release notes. Is this a problem with CPPI 4.1 DMA, or USB CDC notifications?

Dan -