General Steps

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Note

This document is automatically translated using AI. Please excuse any detailed errors. The official English version is still in progress.

This document summarizes the general implementation process of SPI peripherals in ESP-IDF, covering key peripheral configurations, initialization, and common operations, providing a unified implementation reference for different examples.

Mastering the content of this document helps to quickly understand the core usage process of SPI peripherals, facilitating the reuse of common code in different applications.

Configure/Initialize SPI Bus

Before using SPI peripherals, you need to complete the bus configuration, which is used for:

  • Binding pins: Specify the GPIO pins corresponding to the signal lines of the SPI bus, including the clock line (SCLK), master output/slave input (MOSI), master input/slave output (MISO), and chip select line (CS).

  • Allocating hardware resources: In master mode, initializing the bus will allocate DMA, registers, and interrupt resources to support efficient data transmission; in slave mode, the SPI controller will prepare status registers and buffers to receive/send data.

spi_bus_config_t is an SPI bus configuration structure provided by ESP-IDF, used to uniformly set various attributes when initializing the SPI bus. For specific structure members, refer to SPI Driver.

For SPI master mode, after constructing the spi_bus_config_t structure, you also need to call spi_bus_initialize(), to apply the configuration to the SPI controller and allocate hardware resources, in order to carry out data transmission normally. API function description and parameter explanation can refer to SPI Master Driver. For SPI slave mode, usually only need to construct the spi_bus_config_t structure to complete the bus configuration, the SPI controller will use these parameters when initializing the slave interface.

Configure/Initialize SPI Interface

After completing the SPI bus configuration, you need to configure the specific interface for the master or slave, define the logical communication parameters, so that the controller can correctly recognize and handle data transmission between devices.

For SPI master mode, the interface configuration is used to define the parameters for communicating with each slave device on the bus, including clock speed, SPI mode (clock polarity and phase), chip select control, and transaction queue length.

  • Define device handle: The type is spi_device_handle_t, used to identify and manage the slave devices registered on the SPI bus, and initiate transactions or configure device parameters through this handle in master mode.

  • Configure interface parameters: spi_device_interface_config_t is an SPI device interface configuration structure provided by ESP-IDF, used to uniformly set device communication attributes. For specific structure members, refer to SPI Master Driver Program.

  • Initialize Interface: Call spi_bus_add_device() to apply the device configuration to the initialized SPI bus, enabling the host to transfer data with the device. For specific instructions and parameters, refer to SPI Host Driver.

For SPI Slave Mode, the interface configuration is used to set the slave parameters, enabling the SPI slave to recognize the transfer initiated by the host, manage the transaction queue, and correctly handle the received and sent data.

  • Configure Slave Interface Parameters: spi_slave_interface_config_t is a SPI slave interface configuration structure provided by ESP-IDF, used to uniformly set the communication attributes of the slave. For specific structure members, refer to SPI Driver.

  • Initialize Interface: Call spi_slave_initialize() to apply the slave interface configuration, enabling the SPI controller to allocate necessary hardware resources (registers, buffers, DMA channels, etc.), ensuring that the slave can receive and respond to the host’s communication. For specific instructions and parameters, refer to SPI Driver.

SPI Transaction Information

An SPI transaction is an abstract description of a complete SPI data transfer, including the send buffer, receive buffer, transfer length, and related control information. The transaction defines all parameters of a single communication by the host or slave, and the SPI driver completes the data reception and transmission according to this structure.

  1. Define the transaction structure spi_slave_transaction_t. For specific structure members, refer to SPI Slave Driver.

  • The SPI transaction structure describes the transfer parameters, which do not change with each loop, and only need to be defined once during the task or function initialization stage.

  • The transaction structure is usually defined as an array, which is convenient for batch processing and loop access when multiple transactions need to be managed simultaneously (for example, sending multiple buffers at the same time or implementing queue transmission). Even if only a single transaction is used, an array of length 1 can be used to maintain a consistent coding style.

  • When defining, you can zero the structure to ensure that all fields have a definite initial value, avoiding unexpected behavior or data errors caused by uninitialized fields.

  1. In the loop, set the relevant transaction parameters by setting the members in the transaction structure, preparing for subsequent data transmission:

  • Before each send or receive data, the transaction parameters should be set or updated according to actual needs.

  • It is necessary to ensure that the set send and receive buffers have been allocated and are valid before the start of the transmission, to avoid data conflicts or transmission abnormalities caused by modifying the buffer content during the execution of the transaction.

  • The unit of the structure member length is bits, and it needs to be defined by multiplying the number of bytes by 8.

  1. Execute Transaction:

  • For SPI master mode, a SPI transaction can be initiated and waited for completion by calling spi_device_transmit(). This API is a blocking call, which will wait for the transaction to complete before returning, suitable for scenarios that require synchronous sending and receiving of data. For further introduction and parameter description, please refer to SPI Master Driver.

  • For SPI slave mode, a SPI transaction can be initiated and waited for completion by calling spi_slave_transmit(). This API is also a blocking call, which will not return until the master completes a transaction, used for synchronous data transmission and reception. For further introduction and parameter description, please refer to SPI Slave Driver.

Note

If you need to implement asynchronous or continuous transmission, you can use the _queue_trans() series of APIs and cooperate with callbacks or polling to get results, which can improve transmission efficiency.

Pause/Restart the Slave

Pausing the slave can ensure energy saving when the SPI bus is not in use, and at the same time avoid receiving invalid data.

  1. Call spi_slave_disable() to pause the SPI slave interface, allowing the peripheral to enter a low power state.

  2. Call spi_slave_enable() to restart the SPI slave interface, allowing it to continue receiving the next transaction.