MSP432P401R: How to reset DMA buffer?

Hello Yuliy,

There is no Reset command to reset the DMA buffer pointer. You would need to make sure that the DMA channel is enabled only when the Pause occurs to ensure that the 256 bytes from the same telegram is received.

>You would need to make sure that the DMA channel is enabled only when the Pause occurs 

How? I do not know is there pause or not, before I enable UART+DMA. 

And what if I start receiving in a middle of telegramm. 

No possibility to cancel?

>I am not sure what is the source of the data to the UART.
some external device, no other connection is in between..
> sorry no toggle is possible, since there is no other connection but uart.

OKay, means that I have no means to cancel half filled dma buffer?

Hello Yuliy,

If there is no indication to the CPU that there is an incomplete data buffer it is not possible to simply cancel the half filled buffer. If the information can be ascertained, then disabling the UART, disabling the DMA channel, reinitialize the DMA control structure, enable the DMA channel and then enable the UART is the correct method to cancel a previously known incomplete buffer.

Hello Yuliy,

I believe the issue is with the DMA control structure being corrupted, which is why reinitalizing the DMA control structure is helping. If the actual sequence of events for the first corruption are know, we could help you better.

there are 2 types of scenarious that leads to corrupted DMA buffer.

first. the paise between 2 DMA buffer is too small. it comes to Kind of overrun error.

second,  DMA start to listen to wrong time, in a middle of UART Transfer, so it takes part of current UART Telegramm, waits, receive anoter part of second UART Telegramm, viola, we have to reset DMA.

Hello Yuliy,

The DMA is working at full clock speed, while UART is a low speed peripheral. The scaling should allow for a seamless transfer. The second point is about the initialization model. The DMA must be initialized and enabled before UART communication is started.

>The DMA must be initialized and enabled before UART communication is started.

this "must" is a good thing, but when I start an application, I have no means to understand is this time moment is a pause between two UART telegramms or UART is coming..

Hello Yuliy,

When the device starts up, the DMA is the first block that is configured. Then UART is configured. Once UART starts the transfer the DMA can receive data bytes from the UART module. I do not see the issue in that? Could you please clarify?

There are 2 devices that communicate each other.
Device A is a master. It sends, say, 256 Bytes - pause 300 uS - sends 256 Bytes and so on. Last 2 bytes is Kind-of-CRC check
Device B is a slave, it listens.

I do application for the device B. When I enable DMAI do not know it happen to listen in a middle of Master sending or master pause.
No way. Until slave starts and can recognise that something is wrong, I listen from middle to middle.
Now big question,
How to reset DMA?

Hello Yuliy,

The correct method in this case would be to monitor the UART RX line and see if there is a IDLE for 100 us or more. If yes, then that is the correct time to enable the UART as the UART will now receive 256 Bytes from the start rather than during a transfer.

Hello Yuliy,

Yes, monitor the pin in GPIO mode. We now know that there would be 256 bytes of data. Every time there is a 1 -> 0 toggle that means there is a byte being sent and hence reset a timer for 100 us. Once the last 1->0 transition goes, wait for the 100 us timer to elapse. If the timer elapses it means there is no data on the bus for the next 200 us. This 200 us can be used to now initialize the UART and DMA.

Hello Yuliy,

May I mark the forum post "closed". In case you still need help you can reopen the forum post.