DMA Modes

Hi,

We, Vaishali and Priya, project associates at IIT Madras are working on BF 533 to configure it to DMA transfer data from SDRAM to PPI. The Sclock has been configured for 126 MHz and the PPI clock in is provided for from Timer0. When the PPI clock in from Timer0 is configured for 63mhz[as per our requirements] we encounter underrun error. For lower values of frequencies like 42 mhz or less we do not encounter this problem. These are the results we observed when DMA is configured in autobuffer mode. But when we run the DMA in stop/start mode we encounter underrun error at 63 mhz and lesser values of frequencies[of PPI clk] like  42 mhz and 31.5 mhz. We understand that 63 mhz is close to max running freq so experience the discrepancy but why do we encounter underrun at all frequency values in stop start mode of the processor DMA.

I f you can please help us in finding the reason of the problem and its solution it'll be of great help.

 

Thanx

Regards

Vaishalli