Intel® Arria® 10 Hard Processor System Technical Reference Manual

ID 683711
Date 8/28/2023
Public
Document Table of Contents

20.4.4.3. Master SPI and SSP Serial Transfers

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

When the transfer mode is “transmit and receive” or “transmit only” (TMOD = 0 or TMOD = 1, respectively), transfers are terminated by the shift control logic when the transmit FIFO buffer is empty. 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 (TXFTLR) can be used to early interrupt (Transmit FIFO Empty Interrupt) the processor indicating that the transmit FIFO buffer is nearly empty. †

When the DMA is used in conjunction with the SPI master, the transmit data level (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 user may also write a block of data (at least two FIFO buffer entries) into the transmit FIFO buffer before enabling a serial slave. This ensures that serial transmission does not begin until the number of data frames that make up the continuous transfer are present in the transmit FIFO buffer. †

When the transfer mode is “receive only” (TMOD = 2), a serial transfer is started by writing one “dummy” data word into the transmit FIFO buffer when a serial slave is selected. The txd output from the SPI controller is held at a constant logic level for the duration of the serial transfer. The transmit FIFO buffer is popped only once at the beginning and may remain empty for the duration of the serial transfer. The end of the serial transfer is controlled by the “number of data frames” (NDF) field in control register 1 (CTRLR1). †

If, for example, you want to receive 24 data frames from a serial‑slave peripheral, you should program the NDF field with the value 23; the receive logic terminates the serial transfer when the number of frames received is equal to the NDF value plus one. This transfer mode increases the bandwidth of the system bus as the transmit FIFO buffer never needs to be serviced during the transfer. The receive FIFO buffer should be read each time the receive FIFO buffer generates a FIFO full interrupt request to prevent an overflow. †

When the transfer mode is “eeprom_read” (TMOD = 3), a serial transfer is started by writing the opcode or address, or both, into the transmit FIFO buffer when a serial slave (EEPROM) is selected. The opcode and address are transmitted to the EEPROM device, after which read data is received from the EEPROM device and stored in the receive FIFO buffer. The end of the serial transfer is controlled by the NDF field in the control register 1 (CTRLR1).

Note: EEPROM read mode is not supported when the SPI controller is configured to be in the SSP mode.  †

The receive FIFO threshold level (RXF TLR) can be used to give early indication that the receive FIFO buffer is nearly full. When a DMA is used, the receive data level (DMARDLR) can be used to early request the DMA Controller, indicating that the receive FIFO buffer is nearly full. †