DSP56857 datasheet(231/662 Pages) FREESCALE

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Programming Examples

Direct Memory Access (DMA), Rev. 4

Freescale Semiconductor

9-13

9.6.7.2 Source Address High (DMASAH)—Bits 7–0

This is the upper byte of the DMA Source Address. DMA data is read from this address. If

post-incrementing (or decrementing) is enabled, this value is updated with each read transaction.

9.7 Programming Examples

Three different scenarios are described to illustrate the use of DMA.

9.7.1 Peripheral-to-Memory DMA Operation

In the first scenario, transfer data from an SPI peripheral to a 16-word block of data memory

starting at address $1000 is desired. The SPI Data Receive Register is located at X:$1FFFEA.

The SPI receive is assigned to DMA_REQ[1] and is provided in Table 9-10. In this scenario,

assume the SPI is configured to transfer data by16-bit words. We would like the DMA to

interrupt the core when the transfer is completed. To configure the DMA to perform this

operation, follow these seven steps:

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

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

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

4. Write $1000 to the DMA Destination Address (low) register

5. Write $0010 (hex = 16 decimal) to the DMA Transfer Count register

6. Write $0000 to the DMA Circular Queue Size register to disable the circular queue

7. Write $D012 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 (INTRPEND = 0)

•

The DMA data size is set to word (DATASIZE = 1)

•

The SPI peripheral (DMA_REQ[1]) is selected for monitoring.

•

The DMA source is set to not change values, to repeatedly read SPI data from the SPI

Data Receive register (SSIM = 0)

•

The DMA destination address is set to increment (CDSIM = 10) (by words because

DATASIZE = 1)

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