DSP56857 datasheet(234/662 Pages) FREESCALE

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Programming Examples

5685X Digital Signal Controller User Manual, Rev. 4

9-16

Freescale Semiconductor

Note:

In the circular queue mode, the DMA operation runs endlessly until the DMA is

explicitly turned off by the processor. If the byte mode is selected, source and

destination addresses have no boundary restrictions.

Figure 9-11. DMA Circular Queue Operation

To configure the DMA to perform this operation, the following steps would be taken:

1. Write $001F to the DMA Source Address (high) register

2. Write $FFE4 to the DMA Source Address (low) register

3. Write $0000 to the DMA Destination Address (high) register

4. Write $5000 to the DMA Destination Address (low) register

5. Write $0028 (hex = 40 decimal) to the DMA Transfer Count register

6. Write $0190 (hex = 400 decimal) to the DMA Circular Queue Size register

7. Write $D032 to the DMA Transfer Control register

Steps 1 through 6 above may be performed in any order; however, step seven must be performed

last. In step seven follow these steps:

•

The DMA is enabled (DMAON = 1)

•

DMA Interrupts are enabled (INTRON = 1)

•

The DMA Interrupt Pending bit is cleared (INTERPEND = 0)

40-word

packet

40-word

packet

40-word

packet

40-word

packet

40-word

packet

40-word

packet

40-word

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40-word

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40-word

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40-word

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400-Word

Circular

Buffer

$5000

$518F

DMA Intr

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