Stopping Dma Transfers; Switching From Transmit To Transmit/Receive Dma - Analog Devices ADSP-21261 SHARC Hardware Reference Manual

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Programming Model

Stopping DMA Transfers

When performing transmit DMA transfers, data moves through a four

deep SPI DMA FIFO, then into the

shift register. DMA interrupts are latched when the I/O processor moves

the last word from memory to the peripheral. For the SPI, this means that

the SPI "DMA complete" interrupt is latched when there are six words

remaining to be transmitted (four in the FIFO, one in the

and one being shifted out of the shift register). To disable the SPI port

after a DMA transmit operation, use the following steps:

1. Wait for the DMA FIFO to empty. This is done when the

bits (bits 13–12 in the

2. Wait for the

bit, (bit 3) in the

When stopping receive DMA transfers, it is recommended that

programs follow the SPI disable steps provided in

Receive to Receive/Transmit DMA"

3. Wait for the SPI shift register to finish transferring the last word.

This is done when the

becomes one.

4. Disable the SPI ports by setting the

registers to zero.

The following sequence details the steps for switching from transmit to

receive DMA.

registers to empty. This is done when the

registers becomes zero.

bit (bit 0) of the

ADSP-2126x SHARC Processor Hardware Reference

buffers, and finally into the

registers) become zero.

"Switching from

bit (bit 0) of the

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