Need Help on MCF52259 UART access using DMA at lower baud rate having problem...

[MonoromDeb]

Hi

I am using MCF52259, in which i have used DMA for data transfer through UART. At higher baud rate every thing is OK, but at lower baud rate (like 300bps) controller becomes slugish. My all timing is getting messed up. Although 300bps is only required for handshaking purpose after that it moved on to higher baud rate.

Can any one help me on this? I don't want to move from DMA manual transfer, it will impact throughput.

[mjbcswitzerland]

Hi

At the moment I can't imagine how a low baud rate can cause the processor to become sluggish?

A single DMA transfers take place each time the transmit buffer becomes empty and is repeated the number of times programmed. Each single transfer takes only a very short time to complete (ns region) and so at slower baud rates the effect on the processor should be insignificant, as should the case be for much higher baud rates.

Can you explain more about how you are getting this effect? Is your transmitting routine maybe waiting for the DMA controller to signal that the transfer has completed and so spinning on a flag? [In such a case the DMA completion interrupt should be used instead].

Regards

Mark