PSoC6: Getting current DMA destination pointer

[JaSi_1632926]

Hi,

I want to know how to retrieve the current DMA descriptor pointer. I have a SCB UART with DMA on the RX port, which writes into a memory buffer. I can see that the data is retrieved and stored in the buffer, but I don't understand how to get the current memory address.

The cy_stc_dma_descriptor_t struct's dst value doesn't seem to change. Is there any other way to get it?

Thanks, Jacob

[Yeshwanth_KT]

Hi Jacob,

You can use the functions mentioned below to get the current source and destination addresses.

If you have any more doubts please feel free to ask.

Regards,

Yeshwanth

[JaSi_1632926]

Hi,

That gives me an incorrect address - which I guess is because it's using the hardware DMA block as pointer - which is shared between several DMA channels.

The destination address per channel needs to be stored somewhere, but where?

Thanks, Jacob

[JaSi_1632926]

.. and even if I disable all other DMA channels using the same hardware DMA, Cy_DMA_GetActiveDstAddress seems to give me only the pointer I specified when calling Cy_DMA_Descriptor_SetDstAddress, not the actual address currently used (which is an address within the buffer given). I can see that data is added to the buffer, but the adress is never incremented.

[JaSi_1632926]

It seems like the DWn_CH_STRUCTm_CH_IDX register can be used together with the base buffer address to figure out where in the buffer the DMA currently is.

Is this the recommended way?

[Yeshwanth_KT]

Yes, I checked that "Cy_DMA_GetActiveDstAddress()" is getting the destination address set for the current descriptor and not the address of the current transfer. For every Data wire controller there is a structure created as below,

"Cy_DMA_GetActiveDstAddress()" was returning the "ACT_DESCR_DST" from the structure. The one you need is "ACT_DST". Which can be accessed by "DMA_HW->ACT_DST". Please use this to access the active destination.

[JaSi_1632926 · Accepted solution]

I used DMA_HW->CH_STRUCT[DMA_DW_CHANNEL].CH_IDX which is updated exactly as I expect it to be.

[Yeshwanth_KT]

Yes, "DMA_HW->CH_STRUCT[DMA_DW_CHANNEL].CH_IDX" will give you the index of the current transfer. You can calculate address by using the initial destination address and the index obtained.

The easy way is to use "DMA_HW->ACT_DST" which directly gives the calculated address. Use whichever that suits your application well.

Regards,

Yeshwanth