STR720 datasheet(85/401 Pages) STMICROELECTRONICS

85 / 401 page

STR720 - DMA CONTROLLER (DMAC)

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1. Set DMA stream configuration registers writing CIRCULAR bit to’1’ and LAST bit to ‘0’.

2. Proceed fetching the circular buffer using an index to keep trace of last buffer location

used.

3. When the end of transfer condition occurs, stop DMA operation writing DMA_EN to ‘0’.

4. The last buffer location to be used will be indicated by DESTCurrent register pair.

Circular buffer mode has the following limitations:

•

When buffer size is not a multiple of the configured burst size. This is due to the fact

that FIFO is always flushed when the end of buffer is reached, and the resulting runt

burst would not be followed by a transfer moving the remaining locations, located at

the beginning of circular buffer, to complete the programmed burst size.

•

DMALUBuff value, when used, must always be aligned to a buffer location which is a

multiple of the configured burst size and its distance from the current value of TC

(buffer location currently under use) must always be greater than a full burst. This is to

prevent setting of last used buffer location to a place where DMA is already passed or

it is about to pass during the current transfer completion, since DMA controller keeps

operating in parallel to CPU program execution.

•

When memory to memory data transfer is configured on stream 3.

STR720 数据表(PDF) 85 Page - STMicroelectronics