Intel® Stratix® 10 Hard Processor System Technical Reference Manual

ID 683222
Date 11/28/2022
Public

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19.4.5.1. Slave SPI and SSP Serial Transfers 

“Motorola SPI Protocol” and the “Texas Instruments Synchronous Serial Protocol (SSP)” contain a description of the SPI and SSP serial protocols, respectively. †

If the SPI slave is receive only (TMOD=2), the transmit FIFO buffer need not contain valid data because the data currently in the transmit shift register is resent each time the slave device is selected. The TXE error flag in the status register (SR) is not set when TMOD=2. You should mask the Transmit FIFO Empty Interrupt when this mode is used. †

If the SPI slave transmits data to the master, you must ensure that data exists in the transmit FIFO buffer before a transfer is initiated by the serial‑master device. If the master initiates a transfer to the SPI slave when no data exists in the transmit FIFO buffer, an error flag (TXE) is set in the SPI status register, and the previously transmitted data frame is resent on txd. For continuous data transfers, you must ensure that the transmit FIFO buffer does not become empty before all the data have been transmitted. The transmit FIFO threshold level register (TXFTLR) can be used to early interrupt (Transmit FIFO Empty Interrupt) the processor, indicating that the transmit FIFO buffer is nearly empty. When a DMA Controller is used, the DMA transmit data level register (DMATDLR) can be used to early request the DMA Controller, indicating that the transmit FIFO buffer is nearly empty. The FIFO buffer can then be refilled with data to continue the serial transfer. †

The receive FIFO buffer should be read each time the receive FIFO buffer generates a FIFO full interrupt request to prevent an overflow. The receive FIFO threshold level register (RXFTLR) can be used to give early indication that the receive FIFO buffer is nearly full. When a DMA Controller is used, the DMA receive data level register (DMARDLR) can be used to early request the DMA controller, indicating that the receive FIFO buffer is nearly full. †