SPI Module

Since Origin / Contributor Maintainer Source
2017-05-04 Arnim Läuger Arnim Läuger spi.c

SPI Bus

The ESP32 contains 4 SPI bus hosts called SPI, SPI1, HSPI, and VSPI. SPI is locked to flash communication and is not available for the application. SPI1 is currently also tied to flash support, but might be available in the future. Applications can currently only use the HSPI and VSPI hosts.

The host signals can be mapped to any suitable GPIO pins.

Note

The API on ESP32 differs from the API on ESP8266. For backwards compatibility please refer to lua_compat/spi_compat.lua.

spi.master()

Initializes a bus in master mode and returns a bus master object.

Syntax

spi.master(host[, config[, dma]])

Parameters

  • host id, one of
    • spi.SPI1. not supported yet
    • spi.HSPI
    • spi.VSPI
  • config table listing the assigned GPIOs. All signal assignment are optional.
    • sclk
    • mosi
    • miso
    • quadwp
    • quadhd
  • dma set DMA channel (1 or 2) or disable DMA (0), defaults to 1 if omitted. Enabling DMA allows sending and receiving an unlimited amount of bytes but has restrictions in halfduplex mode (see spi.master:device()). Disabling DMA limits a transaction to 32 bytes max.

Not

Omitting the config table returns an SPI bus master object without further initialization. This enables sharing the same SPI host with sdmmc in SD-SPI mode. First call sdmmc.init(sdmmc.VSPI, ...), then spi.master(spi.VSPI).

Returns

SPI bus master object

Example

busmaster_config = {sclk = 19, mosi = 23, miso = 25}
busmaster = spi.master(spi.HSPI, busmaster_config)

Bus Master Object

spi.master:close()

Close the bus host. This fails if there are still devices registered on this bus.

Caution

The bus is also closed when the bus master object is automatically destroyed during garbage collection. Registered devices inherently prevent garbage collection of the bus master object.

Syntax

busmaster:close()

Parameters

none

Returns

nil

spi.master:device()

Adds a device on the given master bus. Up to three devices per bus are supported.

Note

Due to restrictions of the ESP IDF, halfduplex mode does not support DMA with both MOSI and MISO phases. Disable DMA during the call to spi.master() in this case and ensure that transaction data is not larger than 32 bytes.

Syntax

busmaster:device(config)

Parameters

config table describing the device parameters:

  • cs GPIO connected to device's chip-select pin, optional
  • mode SPI mode used for this device (0-3), mandatory
  • freq clock frequency used for this device [Hz], mandatory
  • command_bits amount of bits in command phase (0-16), defaults to 0 if omitted
  • address_bits amount of bits in address phase (0-64), defaults to 0 if omitted
  • dummy_bits amount of dummy bits to insert address and data phase, defaults to 0 if omitted
  • cs_ena_pretrans, optional
  • cs_ena_posttrans, optional
  • duty_cycle_pos, optional
  • tx_lsb_first transmit command/address/data LSB first if true, MSB first otherwise (or if omitted)
  • rx_lsb_first receive data LSB first if true, MSB first otherwise (or if omitted)
  • wire3 use spiq for both transmit and receive if true, use mosi and miso otherwise (or if omitted)
  • positive_cs chip-select is active high during a transaction if true, cs is active low otherwise (or if omitted)
  • halfduplex transmit data before receiving data if true, transmit and receive simultaneously otherwise (or if omitted)
  • clk_as_cs output clock on cs line when cs is active if true, defaults to false if omitted

Returns

SPI device object

Example

device_config = {mode = 0, freq = 1000000}
device_config.cs = 22
dev1 = busmaster:device(device_config)

device_config.cs = 4
dev2 = busmaster:device(device_config)

Device Object

spi.master:device:remove()

Removes a device from the related bus master.

Caution

The device is also removed when the device object is automatically destroyed during garbage collection.

Syntax

device:remove()

Parameters

none

Returns

nil

spi.master:device:transfer()

Initiate an SPI transaction consisting of

  1. assertion of cs signal
  2. optional sending of command bits
  3. optional sending of address bits
  4. optional sending of dummy bits
  5. sending of tx data
  6. concurrent or appended reception of rx data, optional
  7. de-assertion of cs signal

The function returns after the transaction is completed.

Syntax

device:transfer(trans)
device:transfer(txdata)

Parameters

trans table containing the elements of the transaction:

  • command data for command phase, amount of bits was defined during device creation, optional
  • address data for address phase, amount of bits was defined during device creation, optional
  • txdata string of data to be sent to the device, optional
  • rxlen number of bytes to be received, optional
  • mode optional, one of
    • sio transmit in SIO mode, default if omitted
    • dio transmit in DIO mode
    • qio transmit in QIO mode
  • addr_mode transmit address also in selected mode if true, transmit address in SIO otherwise.

txdata string of data to be sent to the device

Returns

String of rxlen length, or #txdata length if rxlen is omitted.

spi.slave()

Initializes a bus in slave mode and returns a slave object. Not yet supported.