SPI / I²S 1..6
The SPI interface offers 2 main functions: SPI and I²S (audio protocol).
There are a total of 6 SPI controllers which can be configured and used independently.
Features
- Full-duplex synchronous transfer (on 3 lines: MOSI, MISO, SCK).
- Simplex synchronous transfer (on 2 lines: MOSI/MISO, SCK).
- 8 or 16 bit data transfer width.
- Master or slave mode.
- Slave select either by hardware or software.
- Interrupt, CRC and DMA support.
Configuration Registers
SPI_CR1 - Configuration register 1
(not used in I²S mode)
| MSTR | 0 | Slave mode (reset state) | ||
| 1 | Master mode | |||
| BR | 000 | BR ⇒ fPCLK2 / 2 (reset state) | 100 | BR ⇒ fPCLK2 / 32 |
| 001 | BR ⇒ fPCLK2 / 4 | 101 | BR ⇒ fPCLK2 / 64 | |
| 010 | BR ⇒ fPCLK2 / 8 | 110 | BR ⇒ fPCLK2 / 128 | |
| 011 | BR ⇒ fPCLK2 / 16 | 111 | BR ⇒ fPCLK2 / 256 | |
| SPE | 0 | SPI disabled (reset state) | ||
| 1 | SPI enabled | |||
| LSBFIRST | 0 | MSB transmitted first (reset state) | ||
| 1 | LSB transmitted first | |||
| SSM | 0 | Slave management by hw (reset state) | ||
| 1 | Slave management by sw | |||
| DFF | 0 | Data frame: 8 bit (reset state) | ||
| 1 | Data frame: 16 bit | |||
SPI_CR2 - Configuration register 2
| SSOE | 0 | Slave select disabled in master mode (reset state) |
| 1 | Slave select enabled in master mode (not for multi master setup) | |
| FRF | 0 | Motorolla frame format (reset state) |
| 1 | Texas Instruments frame format | |
| ERRIE | 0 | Error interrupt disabled (reset state) |
| 1 | Error interrupt enabled | |
| RXNEIE | 0 | RX not empty interrupt disabled (reset state) |
| 1 | RX not empty interrupt enabled | |
| TXEIE | 0 | TX empty interrupt disabled (reset state) |
| 1 | TX empty interrupt enabled |
SPI_CRCPR - CRC polynomial register
(not used in I²S mode)
Contains polynomial used to calculate CRC. Reset value: 0x0007.
SPI_RXCRCR - RX CRC register
(not used in I²S mode)
Contains computed CRC value of received bytes.
SPI_TXCRCR - TX CRC register
(not used in I²S mode)
Contains computed CRC value of transmitted bytes.
SPI_I2SCFGR - I²S configuration register
(not used in SPI mode)
SPI_I2SPR - I²S prescaler register
(not used in SPI mode)
Data Register
SPI_DR - Data register
Data received or to be transmitted. Split into 2 buffers:
- Writing to DR writes to TX Buffer.
- Reading from DR reads from RX Buffer.
Programming Example
The code snippet bellow shows how to configure and use the SPI peripheral.
#include "reg_stm32f4xx.h" RCC->AHBENR[0] |= (0x1 << 0u); /* Enable GPIOA clock */ RCC->APBENR[1] |= (0x1 << 12u); /* Enable SPI1 clock */ /* Configure GPIO pin A.4 to A.7 in alternate function mode. */ GPIOA->MODER &= ~(0xff << 8u); /* Clear existing mode bits 8 to 15. */ GPIOA->MODER |= (0xaa << 8u); /* Set pin 4..7 to alternate function mode. */ GPIOA->OSPEEDR &= ~(0xff << 8u); /* Clear existing output speed bits 8 to 15. */ GPIOA->OSPEEDR |= (0xff << 8u); /* Set pin 4..7 to high speed (100MHz) mode. */ GPIOA->AFR[0] &= ~(0xffff << 16u); /* Clear existing af bits 16 to 31. */ GPIOA->AFR[0] |= (0x5555 << 16u); /* Set pin 4..7 to AF5 (SPI1). */ /* Configure SPI1 in slave mode. */ SPI1->CR1 = 0u; /* Reset SPI1 configuration. */ SPI1->CR2 = 0u; /* Reset SPI1 configuration. */ SPI1->CR1 |= (0x1 << 3u) | /* Select 11,25MHz as baudrate (45 MHz / 4). */ (0x1 << 6u); /* Enable SPI. */