Is it possible to detect when a DMA channel on a Cortex M3 goes idle?

I've just taken over a project developing C code for an STM32 Cortex M3 microcontroller.

An issue that I immediately have is that I have a free running DMA channel that transfers data between 2 USARTs, but on occasions data from another source needs to be sent to the destination USART.

Is there any way to detect when a DMA is busy transferring data or idle, or are there any interrupts triggered when a transfer is complete.

Many thanks for any responses,

Dave

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