SPI Master Driver

SPI Master driver is a program that controls ESP32’s SPI peripherals while they function as masters.

Overview of ESP32’s SPI peripherals

ESP32 integrates four SPI peripherals.

  • SPI0 and SPI1 are used internally to access the ESP32’s attached flash memory and share an arbiter.

    There are quite a few limitations when using SPI Master driver on the SPI1 bus, see Notes on Using the SPI Master driver on SPI1 Bus.

  • SPI2 and SPI3 are general purpose SPI controllers, sometimes referred to as HSPI and VSPI, respectively. They are open to users. SPI2 and SPI3 have independent signal buses with the same respective names. Each bus has three CS lines to drive up to three SPI slaves.

Terminology

The terms used in relation to the SPI master driver are given in the table below.

Term

Definition

Host

The SPI controller peripheral inside ESP32 that initiates SPI transmissions over the bus, and acts as an SPI Master. This may be the SPI2 or SPI3 peripheral. (The driver will also support the SPI1 peripheral in the future.)

Device

SPI slave device. An SPI bus may be connected to one or more Devices. Each Device shares the MOSI, MISO and SCLK signals but is only active on the bus when the Host asserts the Device’s individual CS line.

Bus

A signal bus, common to all Devices connected to one Host. In general, a bus includes the following lines: MISO, MOSI, SCLK, one or more CS lines, and, optionally, QUADWP and QUADHD. So Devices are connected to the same lines, with the exception that each Device has its own CS line. Several Devices can also share one CS line if connected in the daisy-chain manner.

  • MISO

Master In, Slave Out, a.k.a. Q. Data transmission from a Device to Host.

  • MOSI

Master Out, Slave In, a.k.a. D. Data transmission from a Host to Device.

  • SCLK

Serial Clock. Oscillating signal generated by a Host that keeps the transmission of data bits in sync.

  • CS

Chip Select. Allows a Host to select individual Device(s) connected to the bus in order to send or receive data.

  • QUADWP

Write Protect signal. Only used for 4-bit (qio/qout) transactions.

  • QUADHD

Hold signal. Only used for 4-bit (qio/qout) transactions.

  • Assertion

The action of activating a line. The opposite action of returning the line back to inactive (back to idle) is called de-assertion.

Transaction

One instance of a Host asserting a CS line, transferring data to and from a Device, and de-asserting the CS line. Transactions are atomic, which means they can never be interrupted by another transaction.

Launch edge

Edge of the clock at which the source register launches the signal onto the line.

Latch edge

Edge of the clock at which the destination register latches in the signal.

Driver Features

The SPI master driver governs communications of Hosts with Devices. The driver supports the following features:

  • Multi-threaded environments

  • Transparent handling of DMA transfers while reading and writing data

  • Automatic time-division multiplexing of data coming from different Devices on the same signal bus, see SPI Bus Lock.

Warning

The SPI master driver has the concept of multiple Devices connected to a single bus (sharing a single ESP32 SPI peripheral). As long as each Device is accessed by only one task, the driver is thread safe. However, if multiple tasks try to access the same SPI Device, the driver is not thread-safe. In this case, it is recommended to either:

  • Refactor your application so that each SPI peripheral is only accessed by a single task at a time.

  • Add a mutex lock around the shared Device using xSemaphoreCreateMutex.

SPI Transactions

An SPI bus transaction consists of five phases which can be found in the table below. Any of these phases can be skipped.

Phase

Description

Command

In this phase, a command (0-16 bit) is written to the bus by the Host.

Address

In this phase, an address (0-64 bit) is transmitted over the bus by the Host.

Write

Host sends data to a Device. This data follows the optional command and address phases and is indistinguishable from them at the electrical level.

Dummy

This phase is configurable and is used to meet the timing requirements.

Read

Device sends data to its Host.

The attributes of a transaction are determined by the bus configuration structure spi_bus_config_t, device configuration structure spi_device_interface_config_t, and transaction configuration structure spi_transaction_t.

An SPI Host can send full-duplex transactions, during which the read and write phases occur simultaneously. The total transaction length is determined by the sum of the following members:

While the member spi_transaction_t::rxlength only determines the length of data received into the buffer.

In half-duplex transactions, the read and write phases are not simultaneous (one direction at a time). The lengths of the write and read phases are determined by length and rxlength members of the struct spi_transaction_t respectively.

The command and address phases are optional, as not every SPI device requires a command and/or address. This is reflected in the Device’s configuration: if command_bits and/or address_bits are set to zero, no command or address phase will occur.

The read and write phases can also be optional, as not every transaction requires both writing and reading data. If rx_buffer is NULL and SPI_TRANS_USE_RXDATA is not set, the read phase is skipped. If tx_buffer is NULL and SPI_TRANS_USE_TXDATA is not set, the write phase is skipped.

The driver supports two types of transactions: the interrupt transactions and polling transactions. The programmer can choose to use a different transaction type per Device. If your Device requires both transaction types, see Notes on Sending Mixed Transactions to the Same Device.

Interrupt Transactions

Interrupt transactions will block the transaction routine until the transaction completes, thus allowing the CPU to run other tasks.

An application task can queue multiple transactions, and the driver will automatically handle them one-by-one in the interrupt service routine (ISR). It allows the task to switch to other procedures until all the transactions complete.

Polling Transactions

Polling transactions do not use interrupts. The routine keeps polling the SPI Host’s status bit until the transaction is finished.

All the tasks that use interrupt transactions can be blocked by the queue. At this point, they will need to wait for the ISR to run twice before the transaction is finished. Polling transactions save time otherwise spent on queue handling and context switching, which results in smaller transaction intervals. The disadvantage is that the CPU is busy while these transactions are in progress.

The spi_device_polling_end() routine needs an overhead of at least 1 us to unblock other tasks when the transaction is finished. It is strongly recommended to wrap a series of polling transactions using the functions spi_device_acquire_bus() and spi_device_release_bus() to avoid the overhead. For more information, see Bus Acquiring.

Command and Address Phases

During the command and address phases, the members cmd and addr in the struct spi_transaction_t are sent to the bus, nothing is read at this time. The default lengths of the command and address phases are set in spi_device_interface_config_t by calling spi_bus_add_device(). If the flags SPI_TRANS_VARIABLE_CMD and SPI_TRANS_VARIABLE_ADDR in the member spi_transaction_t::flags are not set, the driver automatically sets the length of these phases to default values during Device initialization.

If the lengths of the command and address phases need to be variable, declare the struct spi_transaction_ext_t, set the flags SPI_TRANS_VARIABLE_CMD and/or SPI_TRANS_VARIABLE_ADDR in the member spi_transaction_ext_t::base and configure the rest of base as usual. Then the length of each phase will be equal to command_bits and address_bits set in the struct spi_transaction_ext_t.

Write and Read Phases

Normally, the data that needs to be transferred to or from a Device will be read from or written to a chunk of memory indicated by the members rx_buffer and tx_buffer of the structure spi_transaction_t. If DMA is enabled for transfers, the buffers are required to be:

  1. Allocated in DMA-capable internal memory. If external PSRAM is enabled, this means using pvPortMallocCaps(size, MALLOC_CAP_DMA).

  2. 32-bit aligned (staring from a 32-bit boundary and having a length of multiples of 4 bytes).

If these requirements are not satisfied, the transaction efficiency will be affected due to the allocation and copying of temporary buffers.

Note

Half-duplex transactions with both read and write phases are not supported when using DMA. For details and workarounds, see Known Issues.

Bus Acquiring

Sometimes you might want to send SPI transactions exclusively and continuously so that it takes as little time as possible. For this, you can use bus acquiring, which helps to suspend transactions (both polling or interrupt) to other devices until the bus is released. To acquire and release a bus, use the functions spi_device_acquire_bus() and spi_device_release_bus().

Driver Usage

The example code for the SPI master driver can be found in the peripherals/spi_master directory of ESP-IDF examples.

Transactions with Data Not Exceeding 32 Bits

When the transaction data size is equal to or less than 32 bits, it will be sub-optimal to allocate a buffer for the data. The data can be directly stored in the transaction struct instead. For transmitted data, it can be achieved by using the tx_data member and setting the SPI_TRANS_USE_TXDATA flag on the transmission. For received data, use rx_data and set SPI_TRANS_USE_RXDATA. In both cases, do not touch the tx_buffer or rx_buffer members, because they use the same memory locations as tx_data and rx_data.

Transactions with Integers Other Than uint8_t

An SPI Host reads and writes data into memory byte by byte. By default, data is sent with the most significant bit (MSB) first, as LSB first used in rare cases. If a value less than 8 bits needs to be sent, the bits should be written into memory in the MSB first manner.

For example, if 0b00010 needs to be sent, it should be written into a uint8_t variable, and the length for reading should be set to 5 bits. The Device will still receive 8 bits with 3 additional “random” bits, so the reading must be performed correctly.

On top of that, ESP32 is a little-endian chip, which means that the least significant byte of uint16_t and uint32_t variables is stored at the smallest address. Hence, if uint16_t is stored in memory, bits [7:0] are sent first, followed by bits [15:8].

For cases when the data to be transmitted has the size differing from uint8_t arrays, the following macros can be used to transform data to the format that can be sent by the SPI driver directly:

Notes on Sending Mixed Transactions to the Same Device

To reduce coding complexity, send only one type of transactions (interrupt or polling) to one Device. However, you still can send both interrupt and polling transactions alternately. The notes below explain how to do this.

The polling transactions should be initiated only after all the polling and interrupt transactions are finished.

Since an unfinished polling transaction blocks other transactions, please do not forget to call the function spi_device_polling_end() after spi_device_polling_start() to allow other transactions or to allow other Devices to use the bus. Remember that if there is no need to switch to other tasks during your polling transaction, you can initiate a transaction with spi_device_polling_transmit() so that it will be ended automatically.

In-flight polling transactions are disturbed by the ISR operation to accommodate interrupt transactions. Always make sure that all the interrupt transactions sent to the ISR are finished before you call spi_device_polling_start(). To do that, you can keep calling spi_device_get_trans_result() until all the transactions are returned.

To have better control of the calling sequence of functions, send mixed transactions to the same Device only within a single task.

Notes on Using the SPI Master driver on SPI1 Bus

Note

Though the SPI Bus Lock feature makes it possible to use SPI Master driver on the SPI1 bus, it’s still tricky and needs a lot of special treatment. It’s a feature for advanced developers.

To use SPI Master driver on SPI1 bus, you have to take care of two problems:

  1. The code and data, required at the meanwhile the driver is operating SPI1 bus, should be in the internal memory.

    SPI1 bus is shared among devices and the cache for data (code) in the Flash as well as the PSRAM. The cache should be disabled during the other drivers are operating the SPI1 bus. Hence the data (code) in the flash as well as the PSRAM cannot be fetched at the meanwhile the driver acquires the SPI1 bus by:

    During the time above, all other tasks and most ISRs will be disabled (see IRAM-Safe Interrupt Handlers). Application code and data used by current task should be placed in internal memory (DRAM or IRAM), or already in the ROM. Access to external memory (flash code, const data in the flash, and static/heap data in the PSRAM) will cause a Cache disabled but cached memory region accessed exception. For differences between IRAM, DRAM, and flash cache, please refer to the application memory layout documentation.

    To place functions into the IRAM, you can either:

    1. Add IRAM_ATTR (include “esp_attr.h”) to the function like:

      IRAM_ATTR void foo(void) { }

      Please note that when a function is inlined, it will follow its caller’s segment, and the attribute will not take effect. You may need to use NOLINE_ATTR to avoid this.

    2. Use the noflash placement in the linker.lf. See more in Linker Script Generation. Please note that, some code may be transformed into lookup table in the const data by the compiler, so noflash_text is not safe.

    Please do take care that the optimization level may affect the compiler behavior of inline, or transforming some code into lookup table in the const data, etc.

    To place data into the DRAM, you can either:

    1. Add DRAM_ATTR (include “esp_attr.h”) to the data definition like:

      DRAM_ATTR int g_foo = 3;

    2. Use the noflash placement in the linker.lf. See more in Linker Script Generation.

Please also see the example peripherals/spi_master/hd_eeprom.

GPIO Matrix and IO_MUX

Most of ESP32’s peripheral signals have direct connection to their dedicated IO_MUX pins. However, the signals can also be routed to any other available pins using the less direct GPIO matrix. If at least one signal is routed through the GPIO matrix, then all signals will be routed through it.

The GPIO matrix introduces flexibility of routing but also brings the following disadvantages:

  • Increases the input delay of the MISO signal, which makes MISO setup time violations more likely. If SPI needs to operate at high speeds, use dedicated IO_MUX pins.

  • Allows signals with clock frequencies only up to 40 MHz, as opposed to 80 MHz if IO_MUX pins are used.

Note

For more details about the influence of the MISO input delay on the maximum clock frequency, see Timing Considerations.

The IO_MUX pins for SPI buses are given below.

Pin Name

SPI2

SPI3

GPIO Number

CS0*

15

5

SCLK

14

18

MISO

12

19

MOSI

13

23

QUADWP

2

22

QUADHD

4

21

  • Only the first Device attached to the bus can use the CS0 pin.

Transfer Speed Considerations

There are three factors limiting the transfer speed:

  • Transaction interval

  • SPI clock frequency

  • Cache miss of SPI functions, including callbacks

The main parameter that determines the transfer speed for large transactions is clock frequency. For multiple small transactions, the transfer speed is mostly determined by the length of transaction intervals.

Transaction Interval

Transaction interval is the time that software requires to set up SPI peripheral registers and to copy data to FIFOs, or to set up DMA links.

Interrupt transactions allow appending extra overhead to accommodate the cost of FreeRTOS queues and the time needed for switching between tasks and the ISR.

For interrupt transactions, the CPU can switch to other tasks when a transaction is in progress. This saves the CPU time but increases the interval. See Interrupt Transactions. For polling transactions, it does not block the task but allows to do polling when the transaction is in progress. For more information, see Polling Transactions.

If DMA is enabled, setting up the linked list requires about 2 us per transaction. When a master is transferring data, it automatically reads the data from the linked list. If DMA is not enabled, the CPU has to write and read each byte from the FIFO by itself. Usually, this is faster than 2 us, but the transaction length is limited to 64 bytes for both write and read.

Typical transaction interval timings for one byte of data are given below.

Typical Transaction Time (us)

Interrupt

Polling

DMA

24

8

No DMA

22

7

SPI Clock Frequency

Transferring each byte takes eight times the clock period 8/fspi. If the clock frequency is too high, the use of some functions might be limited. See Timing Considerations.

Cache Miss

The default config puts only the ISR into the IRAM. Other SPI related functions, including the driver itself and the callback, might suffer from the cache miss and will need to wait until the code is read from the flash. Select CONFIG_SPI_MASTER_IN_IRAM to put the whole SPI driver into IRAM and put the entire callback(s) and its callee functions into IRAM to prevent cache miss.

For an interrupt transaction, the overall cost is 20+8n/Fspi[MHz] [us] for n bytes transferred in one transaction. Hence, the transferring speed is: n/(20+8n/Fspi). An example of transferring speed at 8 MHz clock speed is given in the following table.

Frequency

(MHz)

Transaction Interval

(us)

Transaction Length

(bytes)

Total Time

(us)

Total Speed

(KBps)

8

25

1

26

38.5

8

25

8

33

242.4

8

25

16

41

490.2

8

25

64

89

719.1

8

25

128

153

836.6

When a transaction length is short, the cost of transaction interval is high. If possible, try to squash several short transactions into one transaction to achieve a higher transfer speed.

Please note that the ISR is disabled during flash operation by default. To keep sending transactions during flash operations, enable CONFIG_SPI_MASTER_ISR_IN_IRAM and set ESP_INTR_FLAG_IRAM in the member spi_bus_config_t::intr_flags. In this case, all the transactions queued before starting flash operations will be handled by the ISR in parallel. Also note that the callback of each Device and their callee functions should be in IRAM, or your callback will crash due to cache miss. For more details, see IRAM-Safe Interrupt Handlers.

Timing Considerations

As shown in the figure below, there is a delay on the MISO line after the SCLK launch edge and before the signal is latched by the internal register. As a result, the MISO pin setup time is the limiting factor for the SPI clock speed. When the delay is too long, the setup slack is < 0, and the setup timing requirement is violated, which results in the failure to perform the reading correctly.

../../_images/spi_miso.png ../../_images/miso_timing_waveform.png

The maximum allowed frequency is dependent on:

  • input_delay_ns - maximum data valid time on the MISO bus after a clock cycle on SCLK starts

  • If the IO_MUX pin or the GPIO Matrix is used

When the GPIO matrix is used, the maximum allowed frequency is reduced to about 33~77% in comparison to the existing input delay. To retain a higher frequency, you have to use the IO_MUX pins or the dummy bit workaround. You can obtain the maximum reading frequency of the master by using the function spi_get_freq_limit().

Dummy bit workaround: Dummy clocks, during which the Host does not read data, can be inserted before the read phase begins. The Device still sees the dummy clocks and sends out data, but the Host does not read until the read phase comes. This compensates for the lack of the MISO setup time required by the Host and allows the Host to do reading at a higher frequency.

In the ideal case, if the Device is so fast that the input delay is shorter than an APB clock cycle - 12.5 ns - the maximum frequency at which the Host can read (or read and write) in different conditions is as follows:

Frequency Limit (MHz)

Dummy Bits Used By Driver

Comments

GPIO matrix

IO_MUX pins

26.6

80

No

40

–

Yes

Half-duplex, no DMA allowed

If the Host only writes data, the dummy bit workaround and the frequency check can be disabled by setting the bit SPI_DEVICE_NO_DUMMY in the member spi_device_interface_config_t::flags. When disabled, the output frequency can be 80MHz, even if the GPIO matrix is used.

spi_device_interface_config_t::flags

The SPI master driver can work even if the input_delay_ns in the structure spi_device_interface_config_t is set to 0. However, setting an accurate value helps to:

  • Calculate the frequency limit for full-duplex transactions

  • Compensate the timing correctly with dummy bits for half-duplex transactions

You can approximate the maximum data valid time after the launch edge of SPI clocks by checking the statistics in the AC characteristics chapter of your Device’s specification or measure the time on an oscilloscope or logic analyzer.

Please note that the actual PCB layout design and the excessive loads may increase the input delay. It means that non-optimal wiring and/or a load capacitor on the bus will most likely lead to the input delay values exceeding the values given in the Device specification or measured while the bus is floating.

Some typical delay values are shown in the following table.

Device

Input delay (ns)

Ideal Device

0

ESP32 slave using IO_MUX*

50

ESP32 slave using GPIO_MUX*

75

ESP32’s slave device is on a different physical chip.

The MISO path delay (valid time) consists of a slave’s input delay plus master’s GPIO matrix delay. This delay determines the frequency limit above which full-duplex transfers will not work as well as the dummy bits used in the half-duplex transactions. The frequency limit is:

Freq limit [MHz] = 80 / (floor(MISO delay[ns]/12.5) + 1)

The figure below shows the relationship between frequency limit and input delay. Two extra APB clock cycle periods should be added to the MISO delay if the master uses the GPIO matrix.

../../_images/spi_master_freq_tv.png

Corresponding frequency limits for different Devices with different input delay times are shown in the table below.

Master

Input delay (ns)

MISO path delay (ns)

Freq. limit (MHz)

IO_MUX (0ns)

0

0

80

50

50

16

75

75

11.43

GPIO (25ns)

0

25

26.67

50

75

11.43

75

100

8.89

Known Issues

  1. Half-duplex transactions are not compatible with DMA when both writing and reading phases are used.

    If such transactions are required, you have to use one of the alternative solutions:

    1. Use full-duplex transactions instead.

    2. Disable DMA by setting the bus initialization function’s last parameter to 0 as follows:

      ret=spi_bus_initialize(VSPI_HOST, &buscfg, 0);

    This can prohibit you from transmitting and receiving data longer than 64 bytes. 3. Try using the command and address fields to replace the write phase.

  2. Full-duplex transactions are not compatible with the dummy bit workaround, hence the frequency is limited. See dummy bit speed-up workaround.

  3. dummy_bits in spi_device_interface_config_t and spi_transaction_ext_t are not available when SPI read and write phases are both enabled (regardless of full duplex or half duplex mode).

  4. cs_ena_pretrans is not compatible with the command and address phases of full-duplex transactions.

Application Example

The code example for displaying graphics on an ESP32-WROVER-KIT’s 320x240 LCD screen can be found in the peripherals/spi_master directory of ESP-IDF examples.

API Reference - SPI Common

Enumerations

enum spi_host_device_t

Enum with the three SPI peripherals that are software-accessible in it.

Values:

SPI1_HOST = 0

SPI1.

SPI2_HOST = 1

SPI2.

SPI3_HOST = 2

SPI3.

enum spi_event_t

SPI Events.

Values:

SPI_EV_BUF_TX = BIT(0)

The buffer has sent data to master, Slave HD only.

SPI_EV_BUF_RX = BIT(1)

The buffer has received data from master, Slave HD only.

SPI_EV_SEND = BIT(2)

Slave has loaded some data to DMA, and master has received certain number of the data, the number is determined by master. Slave HD only.

SPI_EV_RECV = BIT(3)

Slave has received certain number of data from master, the number is determined by master. Slave HD only.

SPI_EV_CMD9 = BIT(4)

Received CMD9 from master, Slave HD only.

SPI_EV_CMDA = BIT(5)

Received CMDA from master, Slave HD only.

SPI_EV_TRANS = BIT(6)

A transaction has done.

Functions

esp_err_t spi_bus_initialize(spi_host_device_t host_id, const spi_bus_config_t *bus_config, spi_dma_chan_t dma_chan)

Initialize a SPI bus.

Warning

SPI0/1 is not supported

Warning

If a DMA channel is selected, any transmit and receive buffer used should be allocated in DMA-capable memory.

Warning

The ISR of SPI is always executed on the core which calls this function. Never starve the ISR on this core or the SPI transactions will not be handled.

Return

  • ESP_ERR_INVALID_ARG if configuration is invalid

  • ESP_ERR_INVALID_STATE if host already is in use

  • ESP_ERR_NOT_FOUND if there is no available DMA channel

  • ESP_ERR_NO_MEM if out of memory

  • ESP_OK on success

Parameters

  • host_id: SPI peripheral that controls this bus

  • bus_config: Pointer to a spi_bus_config_t struct specifying how the host should be initialized

  • dma_chan: - Selecting a DMA channel for an SPI bus allows transactions on the bus with size only limited by the amount of internal memory.

    • Selecting SPI_DMA_DISABLED limits the size of transactions.

    • Set to SPI_DMA_DISABLED if only the SPI flash uses this bus.

    • Set to SPI_DMA_CH_AUTO to let the driver to allocate the DMA channel.

esp_err_t spi_bus_free(spi_host_device_t host_id)

Free a SPI bus.

Warning

In order for this to succeed, all devices have to be removed first.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_ERR_INVALID_STATE if not all devices on the bus are freed

  • ESP_OK on success

Parameters

  • host_id: SPI peripheral to free

Structures

struct spi_bus_config_t

This is a configuration structure for a SPI bus.

You can use this structure to specify the GPIO pins of the bus. Normally, the driver will use the GPIO matrix to route the signals. An exception is made when all signals either can be routed through the IO_MUX or are -1. In that case, the IO_MUX is used, allowing for >40MHz speeds.

Note

Be advised that the slave driver does not use the quadwp/quadhd lines and fields in spi_bus_config_t refering to these lines will be ignored and can thus safely be left uninitialized.

Public Members

int mosi_io_num

GPIO pin for Master Out Slave In (=spi_d) signal, or -1 if not used.

int miso_io_num

GPIO pin for Master In Slave Out (=spi_q) signal, or -1 if not used.

int sclk_io_num

GPIO pin for Spi CLocK signal, or -1 if not used.

int quadwp_io_num

GPIO pin for WP (Write Protect) signal which is used as D2 in 4-bit communication modes, or -1 if not used.

int quadhd_io_num

GPIO pin for HD (HolD) signal which is used as D3 in 4-bit communication modes, or -1 if not used.

int max_transfer_sz

Maximum transfer size, in bytes. Defaults to 4094 if 0.

uint32_t flags

Abilities of bus to be checked by the driver. Or-ed value of SPICOMMON_BUSFLAG_* flags.

int intr_flags

Interrupt flag for the bus to set the priority, and IRAM attribute, see esp_intr_alloc.h. Note that the EDGE, INTRDISABLED attribute are ignored by the driver. Note that if ESP_INTR_FLAG_IRAM is set, ALL the callbacks of the driver, and their callee functions, should be put in the IRAM.

Macros

SPI_MAX_DMA_LEN
SPI_SWAP_DATA_TX(DATA, LEN)

Transform unsigned integer of length <= 32 bits to the format which can be sent by the SPI driver directly.

E.g. to send 9 bits of data, you can: 

 uint16_t data = SPI_SWAP_DATA_TX(0x145, 9);

Then points tx_buffer to &data.

Parameters

  • DATA: Data to be sent, can be uint8_t, uint16_t or uint32_t.

  • LEN: Length of data to be sent, since the SPI peripheral sends from the MSB, this helps to shift the data to the MSB.

SPI_SWAP_DATA_RX(DATA, LEN)

Transform received data of length <= 32 bits to the format of an unsigned integer.

E.g. to transform the data of 15 bits placed in a 4-byte array to integer: 

 uint16_t data = SPI_SWAP_DATA_RX(*(uint32_t*)t->rx_data, 15);

Parameters

  • DATA: Data to be rearranged, can be uint8_t, uint16_t or uint32_t.

  • LEN: Length of data received, since the SPI peripheral writes from the MSB, this helps to shift the data to the LSB.

SPICOMMON_BUSFLAG_SLAVE

Initialize I/O in slave mode.

SPICOMMON_BUSFLAG_MASTER

Initialize I/O in master mode.

SPICOMMON_BUSFLAG_IOMUX_PINS

Check using iomux pins. Or indicates the pins are configured through the IO mux rather than GPIO matrix.

SPICOMMON_BUSFLAG_GPIO_PINS

Force the signals to be routed through GPIO matrix. Or indicates the pins are routed through the GPIO matrix.

SPICOMMON_BUSFLAG_SCLK

Check existing of SCLK pin. Or indicates CLK line initialized.

SPICOMMON_BUSFLAG_MISO

Check existing of MISO pin. Or indicates MISO line initialized.

SPICOMMON_BUSFLAG_MOSI

Check existing of MOSI pin. Or indicates MOSI line initialized.

SPICOMMON_BUSFLAG_DUAL

Check MOSI and MISO pins can output. Or indicates bus able to work under DIO mode.

SPICOMMON_BUSFLAG_WPHD

Check existing of WP and HD pins. Or indicates WP & HD pins initialized.

SPICOMMON_BUSFLAG_QUAD

Check existing of MOSI/MISO/WP/HD pins as output. Or indicates bus able to work under QIO mode.

SPICOMMON_BUSFLAG_NATIVE_PINS

Type Definitions

typedef spi_common_dma_t spi_dma_chan_t

Enumerations

enum spi_common_dma_t

SPI DMA channels.

Values:

SPI_DMA_DISABLED = 0

Do not enable DMA for SPI.

SPI_DMA_CH1 = 1

Enable DMA, select DMA Channel 1.

SPI_DMA_CH2 = 2

Enable DMA, select DMA Channel 2.

SPI_DMA_CH_AUTO = 3

Enable DMA, channel is automatically selected by driver.

API Reference - SPI Master

Functions

esp_err_t spi_bus_add_device(spi_host_device_t host_id, const spi_device_interface_config_t *dev_config, spi_device_handle_t *handle)

Allocate a device on a SPI bus.

This initializes the internal structures for a device, plus allocates a CS pin on the indicated SPI master peripheral and routes it to the indicated GPIO. All SPI master devices have three CS pins and can thus control up to three devices.

Note

While in general, speeds up to 80MHz on the dedicated SPI pins and 40MHz on GPIO-matrix-routed pins are supported, full-duplex transfers routed over the GPIO matrix only support speeds up to 26MHz.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_ERR_NOT_FOUND if host doesn’t have any free CS slots

  • ESP_ERR_NO_MEM if out of memory

  • ESP_OK on success

Parameters

  • host_id: SPI peripheral to allocate device on

  • dev_config: SPI interface protocol config for the device

  • handle: Pointer to variable to hold the device handle

esp_err_t spi_bus_remove_device(spi_device_handle_t handle)

Remove a device from the SPI bus.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_ERR_INVALID_STATE if device already is freed

  • ESP_OK on success

Parameters

  • handle: Device handle to free

esp_err_t spi_device_queue_trans(spi_device_handle_t handle, spi_transaction_t *trans_desc, TickType_t ticks_to_wait)

Queue a SPI transaction for interrupt transaction execution. Get the result by spi_device_get_trans_result.

Note

Normally a device cannot start (queue) polling and interrupt transactions simultaneously.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_ERR_TIMEOUT if there was no room in the queue before ticks_to_wait expired

  • ESP_ERR_NO_MEM if allocating DMA-capable temporary buffer failed

  • ESP_ERR_INVALID_STATE if previous transactions are not finished

  • ESP_OK on success

Parameters

  • handle: Device handle obtained using spi_host_add_dev

  • trans_desc: Description of transaction to execute

  • ticks_to_wait: Ticks to wait until there’s room in the queue; use portMAX_DELAY to never time out.

esp_err_t spi_device_get_trans_result(spi_device_handle_t handle, spi_transaction_t **trans_desc, TickType_t ticks_to_wait)

Get the result of a SPI transaction queued earlier by spi_device_queue_trans.

This routine will wait until a transaction to the given device succesfully completed. It will then return the description of the completed transaction so software can inspect the result and e.g. free the memory or re-use the buffers.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_ERR_TIMEOUT if there was no completed transaction before ticks_to_wait expired

  • ESP_OK on success

Parameters

  • handle: Device handle obtained using spi_host_add_dev

  • trans_desc: Pointer to variable able to contain a pointer to the description of the transaction that is executed. The descriptor should not be modified until the descriptor is returned by spi_device_get_trans_result.

  • ticks_to_wait: Ticks to wait until there’s a returned item; use portMAX_DELAY to never time out.

esp_err_t spi_device_transmit(spi_device_handle_t handle, spi_transaction_t *trans_desc)

Send a SPI transaction, wait for it to complete, and return the result.

This function is the equivalent of calling spi_device_queue_trans() followed by spi_device_get_trans_result(). Do not use this when there is still a transaction separately queued (started) from spi_device_queue_trans() or polling_start/transmit that hasn’t been finalized.

Note

This function is not thread safe when multiple tasks access the same SPI device. Normally a device cannot start (queue) polling and interrupt transactions simutanuously.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_OK on success

Parameters

  • handle: Device handle obtained using spi_host_add_dev

  • trans_desc: Description of transaction to execute

esp_err_t spi_device_polling_start(spi_device_handle_t handle, spi_transaction_t *trans_desc, TickType_t ticks_to_wait)

Immediately start a polling transaction.

Note

Normally a device cannot start (queue) polling and interrupt transactions simutanuously. Moreover, a device cannot start a new polling transaction if another polling transaction is not finished.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_ERR_TIMEOUT if the device cannot get control of the bus before ticks_to_wait expired

  • ESP_ERR_NO_MEM if allocating DMA-capable temporary buffer failed

  • ESP_ERR_INVALID_STATE if previous transactions are not finished

  • ESP_OK on success

Parameters

  • handle: Device handle obtained using spi_host_add_dev

  • trans_desc: Description of transaction to execute

  • ticks_to_wait: Ticks to wait until there’s room in the queue; currently only portMAX_DELAY is supported.

esp_err_t spi_device_polling_end(spi_device_handle_t handle, TickType_t ticks_to_wait)

Poll until the polling transaction ends.

This routine will not return until the transaction to the given device has succesfully completed. The task is not blocked, but actively busy-spins for the transaction to be completed.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_ERR_TIMEOUT if the transaction cannot finish before ticks_to_wait expired

  • ESP_OK on success

Parameters

  • handle: Device handle obtained using spi_host_add_dev

  • ticks_to_wait: Ticks to wait until there’s a returned item; use portMAX_DELAY to never time out.

esp_err_t spi_device_polling_transmit(spi_device_handle_t handle, spi_transaction_t *trans_desc)

Send a polling transaction, wait for it to complete, and return the result.

This function is the equivalent of calling spi_device_polling_start() followed by spi_device_polling_end(). Do not use this when there is still a transaction that hasn’t been finalized.

Note

This function is not thread safe when multiple tasks access the same SPI device. Normally a device cannot start (queue) polling and interrupt transactions simutanuously.

Return

  • ESP_ERR_INVALID_ARG if parameter is invalid

  • ESP_OK on success

Parameters

  • handle: Device handle obtained using spi_host_add_dev

  • trans_desc: Description of transaction to execute

esp_err_t spi_device_acquire_bus(spi_device_handle_t device, TickType_t wait)

Occupy the SPI bus for a device to do continuous transactions.

Transactions to all other devices will be put off until spi_device_release_bus is called.

Note

The function will wait until all the existing transactions have been sent.

Return

  • ESP_ERR_INVALID_ARG : wait is not set to portMAX_DELAY.

  • ESP_OK : Success.

Parameters

  • device: The device to occupy the bus.

  • wait: Time to wait before the the bus is occupied by the device. Currently MUST set to portMAX_DELAY.

void spi_device_release_bus(spi_device_handle_t dev)

Release the SPI bus occupied by the device. All other devices can start sending transactions.

Parameters

  • dev: The device to release the bus.

int spi_cal_clock(int fapb, int hz, int duty_cycle, uint32_t *reg_o)

Calculate the working frequency that is most close to desired frequency, and also the register value.

Parameters

  • fapb: The frequency of apb clock, should be APB_CLK_FREQ.

  • hz: Desired working frequency

  • duty_cycle: Duty cycle of the spi clock

  • reg_o: Output of value to be set in clock register, or NULL if not needed.

Return

Actual working frequency that most fit.

int spi_get_actual_clock(int fapb, int hz, int duty_cycle)

Calculate the working frequency that is most close to desired frequency.

Return

Actual working frequency that most fit.

Parameters

  • fapb: The frequency of apb clock, should be APB_CLK_FREQ.

  • hz: Desired working frequency

  • duty_cycle: Duty cycle of the spi clock

void spi_get_timing(bool gpio_is_used, int input_delay_ns, int eff_clk, int *dummy_o, int *cycles_remain_o)

Calculate the timing settings of specified frequency and settings.

Note

If **dummy_o* is not zero, it means dummy bits should be applied in half duplex mode, and full duplex mode may not work.

Parameters

  • gpio_is_used: True if using GPIO matrix, or False if iomux pins are used.

  • input_delay_ns: Input delay from SCLK launch edge to MISO data valid.

  • eff_clk: Effective clock frequency (in Hz) from spi_cal_clock.

  • dummy_o: Address of dummy bits used output. Set to NULL if not needed.

  • cycles_remain_o: Address of cycles remaining (after dummy bits are used) output.

    • -1 If too many cycles remaining, suggest to compensate half a clock.

    • 0 If no remaining cycles or dummy bits are not used.

    • positive value: cycles suggest to compensate.

int spi_get_freq_limit(bool gpio_is_used, int input_delay_ns)

Get the frequency limit of current configurations. SPI master working at this limit is OK, while above the limit, full duplex mode and DMA will not work, and dummy bits will be aplied in the half duplex mode.

Return

Frequency limit of current configurations.

Parameters

  • gpio_is_used: True if using GPIO matrix, or False if native pins are used.

  • input_delay_ns: Input delay from SCLK launch edge to MISO data valid.

Structures

struct spi_device_interface_config_t

This is a configuration for a SPI slave device that is connected to one of the SPI buses.

Public Members

uint8_t command_bits

Default amount of bits in command phase (0-16), used when SPI_TRANS_VARIABLE_CMD is not used, otherwise ignored.

uint8_t address_bits

Default amount of bits in address phase (0-64), used when SPI_TRANS_VARIABLE_ADDR is not used, otherwise ignored.

uint8_t dummy_bits

Amount of dummy bits to insert between address and data phase.

uint8_t mode

SPI mode, representing a pair of (CPOL, CPHA) configuration:

  • 0: (0, 0)

  • 1: (0, 1)

  • 2: (1, 0)

  • 3: (1, 1)

uint16_t duty_cycle_pos

Duty cycle of positive clock, in 1/256th increments (128 = 50%/50% duty). Setting this to 0 (=not setting it) is equivalent to setting this to 128.

uint16_t cs_ena_pretrans

Amount of SPI bit-cycles the cs should be activated before the transmission (0-16). This only works on half-duplex transactions.

uint8_t cs_ena_posttrans

Amount of SPI bit-cycles the cs should stay active after the transmission (0-16)

int clock_speed_hz

Clock speed, divisors of 80MHz, in Hz. See SPI_MASTER_FREQ_*.

int input_delay_ns

Maximum data valid time of slave. The time required between SCLK and MISO valid, including the possible clock delay from slave to master. The driver uses this value to give an extra delay before the MISO is ready on the line. Leave at 0 unless you know you need a delay. For better timing performance at high frequency (over 8MHz), it’s suggest to have the right value.

int spics_io_num

CS GPIO pin for this device, or -1 if not used.

uint32_t flags

Bitwise OR of SPI_DEVICE_* flags.

int queue_size

Transaction queue size. This sets how many transactions can be ‘in the air’ (queued using spi_device_queue_trans but not yet finished using spi_device_get_trans_result) at the same time.

transaction_cb_t pre_cb

Callback to be called before a transmission is started.

This callback is called within interrupt context should be in IRAM for best performance, see “Transferring Speed” section in the SPI Master documentation for full details. If not, the callback may crash during flash operation when the driver is initialized with ESP_INTR_FLAG_IRAM.

transaction_cb_t post_cb

Callback to be called after a transmission has completed.

This callback is called within interrupt context should be in IRAM for best performance, see “Transferring Speed” section in the SPI Master documentation for full details. If not, the callback may crash during flash operation when the driver is initialized with ESP_INTR_FLAG_IRAM.

struct spi_transaction_t

This structure describes one SPI transaction. The descriptor should not be modified until the transaction finishes.

Public Members

uint32_t flags

Bitwise OR of SPI_TRANS_* flags.

uint16_t cmd

Command data, of which the length is set in the command_bits of spi_device_interface_config_t.

NOTE: this field, used to be “command” in ESP-IDF 2.1 and before, is re-written to be used in a new way in ESP-IDF 3.0.

Example: write 0x0123 and command_bits=12 to send command 0x12, 0x3_ (in previous version, you may have to write 0x3_12).

uint64_t addr

Address data, of which the length is set in the address_bits of spi_device_interface_config_t.

NOTE: this field, used to be “address” in ESP-IDF 2.1 and before, is re-written to be used in a new way in ESP-IDF3.0.

Example: write 0x123400 and address_bits=24 to send address of 0x12, 0x34, 0x00 (in previous version, you may have to write 0x12340000).

size_t length

Total data length, in bits.

size_t rxlength

Total data length received, should be not greater than length in full-duplex mode (0 defaults this to the value of length).

void *user

User-defined variable. Can be used to store eg transaction ID.

const void *tx_buffer

Pointer to transmit buffer, or NULL for no MOSI phase.

uint8_t tx_data[4]

If SPI_TRANS_USE_TXDATA is set, data set here is sent directly from this variable.

void *rx_buffer

Pointer to receive buffer, or NULL for no MISO phase. Written by 4 bytes-unit if DMA is used.

uint8_t rx_data[4]

If SPI_TRANS_USE_RXDATA is set, data is received directly to this variable.

struct spi_transaction_ext_t

This struct is for SPI transactions which may change their address and command length. Please do set the flags in base to SPI_TRANS_VARIABLE_CMD_ADR to use the bit length here.

Public Members

struct spi_transaction_t base

Transaction data, so that pointer to spi_transaction_t can be converted into spi_transaction_ext_t.

uint8_t command_bits

The command length in this transaction, in bits.

uint8_t address_bits

The address length in this transaction, in bits.

uint8_t dummy_bits

The dummy length in this transaction, in bits.

Macros

SPI_MASTER_FREQ_8M

SPI master clock is divided by 80MHz apb clock. Below defines are example frequencies, and are accurate. Be free to specify a random frequency, it will be rounded to closest frequency (to macros below if above 8MHz). 8MHz

SPI_MASTER_FREQ_9M

8.89MHz

SPI_MASTER_FREQ_10M

10MHz

SPI_MASTER_FREQ_11M

11.43MHz

SPI_MASTER_FREQ_13M

13.33MHz

SPI_MASTER_FREQ_16M

16MHz

SPI_MASTER_FREQ_20M

20MHz

SPI_MASTER_FREQ_26M

26.67MHz

SPI_MASTER_FREQ_40M

40MHz

SPI_MASTER_FREQ_80M

80MHz

SPI_DEVICE_TXBIT_LSBFIRST

Transmit command/address/data LSB first instead of the default MSB first.

SPI_DEVICE_RXBIT_LSBFIRST

Receive data LSB first instead of the default MSB first.

SPI_DEVICE_BIT_LSBFIRST

Transmit and receive LSB first.

SPI_DEVICE_3WIRE

Use MOSI (=spid) for both sending and receiving data.

SPI_DEVICE_POSITIVE_CS

Make CS positive during a transaction instead of negative.

SPI_DEVICE_HALFDUPLEX

Transmit data before receiving it, instead of simultaneously.

SPI_DEVICE_CLK_AS_CS

Output clock on CS line if CS is active.

SPI_DEVICE_NO_DUMMY

There are timing issue when reading at high frequency (the frequency is related to whether iomux pins are used, valid time after slave sees the clock).

  • In half-duplex mode, the driver automatically inserts dummy bits before reading phase to fix the timing issue. Set this flag to disable this feature.

  • In full-duplex mode, however, the hardware cannot use dummy bits, so there is no way to prevent data being read from getting corrupted. Set this flag to confirm that you’re going to work with output only, or read without dummy bits at your own risk.

SPI_DEVICE_DDRCLK
SPI_TRANS_MODE_DIO

Transmit/receive data in 2-bit mode.

SPI_TRANS_MODE_QIO

Transmit/receive data in 4-bit mode.

SPI_TRANS_USE_RXDATA

Receive into rx_data member of spi_transaction_t instead into memory at rx_buffer.

SPI_TRANS_USE_TXDATA

Transmit tx_data member of spi_transaction_t instead of data at tx_buffer. Do not set tx_buffer when using this.

SPI_TRANS_MODE_DIOQIO_ADDR

Also transmit address in mode selected by SPI_MODE_DIO/SPI_MODE_QIO.

SPI_TRANS_VARIABLE_CMD

Use the command_bits in spi_transaction_ext_t rather than default value in spi_device_interface_config_t.

SPI_TRANS_VARIABLE_ADDR

Use the address_bits in spi_transaction_ext_t rather than default value in spi_device_interface_config_t.

SPI_TRANS_VARIABLE_DUMMY

Use the dummy_bits in spi_transaction_ext_t rather than default value in spi_device_interface_config_t.

SPI_TRANS_SET_CD

Set the CD pin.

Type Definitions

typedef struct spi_transaction_t spi_transaction_t
typedef void (*transaction_cb_t)(spi_transaction_t *trans)
typedef struct spi_device_t *spi_device_handle_t

Handle for a device on a SPI bus.

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