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DMA Transmit Protocol in Slave Mode
SPRU760B
The protocol has several steps:
Step 1: MCU-DSP writes to the setup and control registers (SPI_SET1,
SPI_SET2, and SPI_CTRL).
When DMA_EN is set, a transmit DMA request is generated, once
the WR bit is set.
Step 2: The DMA writes the data in the transmit register (SPI_TX). Once the
data is written:
The transmit DMA request is cleared (TX_NDMA_REQ goes
-
high).
TX_EMPTY is reset in the data status register (SPI_DSR).
-
The transmit register (SPI_TX) is copied into the shift register
-
(SPI_SR).
If CEi = 0 in SPI_SET2, the transmission starts as soon as the
-
slave device enable goes low (nSPEN0) and the shift register
clock is activated (SRCLK).
Step 3: When the transmission is completed:
TX_EMPTY is set in the data status register (SPI_DSR).
-
A transmit DMA request is generated.
-
Another transmission can start (Step2 → Step3 → Step2 →
-
Step3...).
To stop the process, the MCU-DSP has to reset the WR bit in the con-
trol register (SPI_CTRL).
SPI Master/Slave
Serial Interfaces
43
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