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DMA Transmit and Receive 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 the DMA_EN and WR bits are set, a transmit DMA request is
generated.
Step 2: The DMA writes the data in the transmit register (SPI_TX). Once the
data is written:
The transmit DMA request is released.
-
The TX_EMPTY status bit 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 and reception start as soon
as the slave device enable goes low (nSPEN0) and the shift register
clock is activated (SRCLK).
Step 3: When the transmission and the reception are completed:
The shift register (SPI_SR) is copied into the receive register
-
(SPI_RX).
The RX_FULL and TX_EMPTY bits are set in the data status
-
register (SPI_DSR).
A receive DMA request is generated.
-
Step 4: Once the DMA reads the receive register (SPI_RX):
The RX_FULL status bit is reset in the data status register
-
(SPI_DSR).
The receive DMA request is released.
-
A transmit DMA request is generated.
-
Another transmission and reception can start.
-
To stop the process, the MCU-DSP must reset the RD and WR bits
in the control register (SPI_CTRL).
SPI Master/Slave
Serial Interfaces
47
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