AM335x USB BULK with CCPI DMA

Moving this to the Starterware forum.

Hello emUSB Team

Unfortunately we do not have any example which exposes a generic bulk interface using DMA. Could you please go through the MSD example and post specific questions so that I can help you. 

Hello Vineeth,

the MSD example quite confusing. The CPPI DMA is initialized separately from the other USB stuff. Is this intended?

However, we have tried to re-use the CPPI DMA functions and adapted them into our driver.
The main problem is that after we have written a DMA descriptor and pushed it into the queue and then trigger a RX transfer (Datatranfer Host->Device), I immediately get an RX starvation interrupt.
The appropiate endpoint has been configured for DMA mode and the EP CPPI DMA EP mode is set to transparent mode.
Any clues?

Hi emUSB Team,

Please check below thread which may help you to improve throughput.

Dear Rajasekaran K,

In the http://e2e.ti.com/support/dsp/tms320c6000_high_performance_dsps/f/115/t/270083.aspx thread you are saying that the usb_dev_bulk example has not been officially released and we do not seem to be able to find it.

Would it be possible to send us the usb_dev_bulk example?

Best regards

emUSB Team

Hello emUSB Team,

The USB stack available with AM335x was initially written for stellaris product chain ( a micro-controller series). CPPI DMA support was added to an existing USB stack and hence CPPI DMA is initialized separately. You would have noticed that this same code base also works without CPPI DMA - which can be done by un-defining "DMA_MODE" macro.

CPPI DMA working:

Prepare Buffer descriptor(BD) --> push into respective submit Queue --> On proper transfer completion --> BD is moved to completion Q.

In the case of RX : We prepare BD and push them into the submit Q of the respective channel. As and when data arrives the BDs of that channel would be used up by the CPPI DMA and data moved to the buffers described in the BDs. One point that should be noted is that the CPPI dma imposes certain "alignment " restrictions for the buffers to be used in the BDs. This is the reason you would find that the CPPI dma driver uses its own buffers into which user data is copied. From the perspective of performance this could be an issue and can be handled by defining aligned user buffers. 

Coming back to your problem - the question that begs to be asked is , how many bytes are you trying to transfer from the host and how many (512 bytes) RX BDs have you queued up ? RX starvation interrupt occurs when there are no BDs to receive your data.

Hi emUSB Team,

Sorry for the delayed response. You shall get the source from your TI FAE.

Thanks.