AM6442: XUART data transfer with BCDMA

Hi Berlam,

To dive more deep into your usecase:

• You want to read data from UART RX pin and append it to RINGACC(Using Block Copy DMA)
• Once the threshold of 128 bytes is reached, all 128 bytes will be transferred to DESTINATION_ADDRESS(Using Block Copy DMA)

Berlam Karli said:

However, when the data did not reach the desired size, I could not find any way to access the data in RINGACC without BCDMA transfer.

Can you clarify this statement a little more ?

Also I am assuming you have the code working till transferring data to DESTINATION_ADDRESS when the RINGACC hits 128 bytes.

If you do have, could you share it to me.

Best Regards,

Vaibhav

Hi,

To briefly talk about the application I want to make;

Actually, I want to send the data I read over UART to the destination address when it reaches 128bytes with the help of DMSS/BCDMA.
However, even if the data size in DMSS/BCDMA does not reach 128 bytes, I want to access the buffer where the data is temporarily stored in DMSS and read the data whenever I want.

For this application, I thought it would be more appropriate to use BCDMA, and now, when the data size read over UART reaches 128 bytes, I can write the data to the address I want. However, since I do not know where the data read over UART is stored until it reaches 128 bytes, I cannot access the already incoming data.

Vaibhav Kumar said:

Berlam Karli said:

However, when the data did not reach the desired size, I could not find any way to access the data in RINGACC without BCDMA transfer.

Here, I thought that the data read over UART will be stored in RINGACC until I perform BCDMA transfer, so I need to access RINGACC. However, I am not sure that the data I read over UART is stored in RINGACC in DMSS.

In which unit is the read data stored in DMSS until it reaches the size I want before BCDMA transfer?
Is there a way to access the data that has been read so far before the BCDMA transfer takes place? If yes, can you share an example?

Thank you,

B. Karli

Hi Berlam,

Please expect a response by EOD.

I am going to look for the part where you can access the already read data before BCDMA transfer begins.

Regards,

Vaibhav

Hi Vaibhav,

I've been dealing with this task for a very long time, so I'll be eagerly awaiting your response.

Thank you.

B. Karli

Hi Berlam,

There are two additional threads on this.
1. https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1263588/am6442-am6442-question-about-bcdma-uart-example
2. e2e.ti.com/.../am6442-question-about-bcdma-uart-example

Closing them and will reply here itself.

I have seen you pointed to one thread where there is UART_RX_DMA example. I am going through it and will check internally for the register where you can access the received UART data.

Regards,

Vaibhav

Hi Vaibhav,

Yes, actually I opened other threads to solve the same problem. So it will be enough for me.
Impatiently waiting for your solution?

Thank you,

B. Karli

Hi Berlam,

Have you looked at the following register?

Regards,

Vaibhav

Hi Berlam,

Can you please confirm why you wanted to go UART with BCDMA rather than UART with PKTDMA?

Regards,

S.Anil.

Hi Vaibhav,

The UART_RHR register can store data up to 64 bytes, but when I use it with DMSS structure, I can transfer very large data. So I don't think that data is stored in this register before DMA transfer.

https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1215616/questions-about-dmss-bcdma-pktdma-and-pdma/4597533?tisearch=e2e-sitesearch&keymatch=uart_rx_dma%2525252520bcdma%2525252520example#4597533

For example, in the application here, the transfer is performed when the data size reaches 128 bytes. Shouldn't I be able to transfer data up to a maximum of 64 bytes if this was stored in the register?

Until a week ago, I thought that it could be stored in a hardware register, but when I examined the DMSS and UART architecture in detail, I could not find such a buffer in both architectures. Now I think it is kept in a buffer created by the SDK in the background.

Do you think such a structure is possible?

Thank you very much for your interest.

B. Karli

Hi Swargam,

Actually, I don't insist on using BCDMA.
Basically what I want to do is; To transfer the 128 bytes of data I received over UART to the memory region I want in a single cycle using DMA and to create an interrupt when the transfer is complete. (I can do this with both PKTDMA and BCDMA).
But one of the tasks I have to do is this. Even if 128 bytes are not received and no interrupt occurs, I want to access the data read so far.
Actually, my expectation is that the DMSS unit, when each byte of data is read over UART, brings the data to the buffer I specified and when it reaches the desired transfer size, it informs the CPU by creating an interrupt. However, as can be seen from the above example and SDK: UART Echo Example examples, it does the data transfer when it reaches the size I want.
Since I do not know where the data is stored until the transfer is performed, I cannot access the data until the data size reaches 128 bytes.

Thank you.

B. Karli

Hi,

Please can you help me quickly, I have been dealing with this problem for a very long time, I need to finish it urgently.

B. Karli

Hello Karli,

Berlam Karli said:

But one of the tasks I have to do is this. Even if 128 bytes are not received and no interrupt occurs, I want to access the data read so far.

We are recommended to use the below approach:

When you use the DMA, you should specify the length, wait for the completion of the interrupt, and read the destination buffer.

If you really want to read data before completion of length, just try the below method. We do not recommend this method, and I never checked on my Hw.

You don't need to go with UART and BCDMA for your requirement . You can go with UART+PKATDMA.

and call the below API get the 

Regards,

S.Anil.

Hi Swargam,

First of all, thank you for interest in my question.

I tried the method you mentioned but the Udma_chGetStats function returns 0 until the DMA transfer is complete. So it returns 0 until the interrupt occurs and is cached. Returns the number of bytes received so far after the interrupt occurred and the data was cached. And invalidate didn't work either.

I guess I am not explaining well what I want to do because it is very unreasonable that we cannot find a solution to such a simple problem.

That's why I want to tell you again in detail.

I want the DMA unit to move the data to a circular buffer every time a byte of data is received over the UART and to create an interrupt when the number of incoming bytes reaches the number I want. In fact, the DMA unit needs to write the data it brings to the nose pointer and the software reads it from the tail pointer and creates an interrupt when it reaches the buffer limit.
It's that simple.

However, this is not the case in all shared examples and in my own experiments. The number of incoming bytes is not brought to the buffer until it reaches the number I have specified, when it reaches all of them are brought in at once. Therefore, the purpose of the circular buffer is not fulfilled because I cannot access the incoming data instantly.

But when I read the user reference manual I understand that this is possible.

If you think that this is not possible with interrupt, I can give up my interrupt request.

I'm leaving the code I'm working on right now here./cfs-file/__key/communityserver-discussions-components-files/791/UART_5F00_Dma_5F00_Interrupt.zip

Please share an example or constructive suggestion where I can now solve this problem, because it's annoying that I have to deal with such a simple task for so long.

Thank you.

B. Karli 

Berlam Karli said:

However, this is not the case in all shared examples and in my own experiments. The number of incoming bytes is not brought to the buffer until it reaches the number I have specified, when it reaches all of them are brought in at once. Therefore, the purpose of the circular buffer is not fulfilled because I cannot access the incoming data instantly.

Hello Karli,

DMA can be used to generate an event for the user when it completes the date transfer operation from Periperhal to memory or vice versa.

The user can't access the DMA buffer until the operation is done, and we don't have examples like reading internal DMA buffers instantly without completion of data transfer operations, which is not the use case of DMA.

If you need the DMA trigger based on your length, you can try to change the TR. Other than this method, you can't access the DMA buffer instantly.

Regards,

S.Anil.