When you step through with the debugger, stop at the point just after you expect the USART to start sending. Check the status register for the USART and the DMA channel, assuming you are using block DMA output (that's the most efficient way to send a block of data out the USART). Also check the NVIC registers to make sure the right vectors are enabled. Set breakpoints at the start of your USART and DMA interrupt handlers to verify the handler is being reached properly.
Above all make sure you are trapping system faults, especially hard fault, otherwise you won't have a clue as to what's happening.
If debugging is too complicated...keep using the Keil compiler since you know it works.
Jack Peacock
