SPI

SPI

Initialization

Before any operations related to SPI, one the following function must be called to initialize the system:

init_spi(devices::String; kwargs...); kwargs...
init_spi(devices::AbstractVector{String}; kwargs...

These functions initialize the SPI devices. devices can be a string with the path to spidev or a vector of strings with a set of SPI devices that will be initialized.

The following keywords are supported:

Notice that all keywords can be a Integer, when the configuration will be applied to all SPI devices, or a Vector of Integers, when different configurations can be applied to the initialized devices.

Note

These functions open the device(s) /dev/spidevX.X passed to the argument devices. Thus, make sure that the user has permissions to read and write this file.

julia> init_spi("/dev/spidev0.0")

julia> init_spi(["/dev/spiddev0.0", "/dev/spidev0.1"])

julia> init_spi("/dev/spidev0.0", max_speed_hz = 1000)

Modes

The SPI mode can be selected using the following constants that were obtained from spidev.h (Linux 4.19 tree):

BaremetalPi.SPI_CPHA      = 0x01
BaremetalPi.SPI_CPOL      = 0x02

BaremetalPi.SPI_MODE_0    = (0|0)
BaremetalPi.SPI_MODE_1    = (0|SPI_CPHA)
BaremetalPi.SPI_MODE_2    = (SPI_CPOL|0)
BaremetalPi.SPI_MODE_3    = (SPI_CPOL|SPI_CPHA)

BaremetalPi.SPI_CS_HIGH   = 0x04
BaremetalPi.SPI_LSB_FIRST = 0x08
BaremetalPi.SPI_3WIRE     = 0x10
BaremetalPi.SPI_LOOP      = 0x20
BaremetalPi.SPI_NO_CS     = 0x40
BaremetalPi.SPI_READY     = 0x80
julia> init_spi("/dev/spidev0.0", mode = BaremetalPi.SPI_MODE_0 |
                                         BaremetalPi.SPI_CS_HIGH)

Transfer

This package support full-duplex transfer using the functions spi_transfer and spi_transfer! as follows.

spi_transfer!(devid, tx_buf, rx_buf; kwargs...)

Execute a full duplex transfer to SPI device devid. devid is the ID of the SPI device considering the initialization order when the function init_spi was called.

tx_buf can be a vector of Integer, in which only one message will be sent, or a vector of vectors of Integer, in which multiple messages will be sent.

The received data will be stored in rx_buf that must have the same type of tx_buf and enough size.

This function returns the number of bytes received.

The following keywords are available:

julia> tx_buf = [0x01, 0x80, 0x00]
3-element Array{UInt8,1}:
 0x01
 0x80
 0x00

julia> rx_buf = zeros(UInt8, 3)
3-element Array{UInt8,1}:
 0x00
 0x00
 0x00

julia> spi_transfer!(1, tx_buf, rx_buf)
3

julia> rx_buf
3-element Array{UInt8,1}:
 0x00
 0x01
 0xef

julia> tx_buf = [ [0x01, 0x80, 0x00] for i = 1:3 ]
3-element Array{Array{UInt8,1},1}:
 [0x01, 0x80, 0x00]
 [0x01, 0x80, 0x00]
 [0x01, 0x80, 0x00]

julia> rx_buf = zeros.(UInt8, length.(tx_buf))
3-element Array{Array{UInt8,1},1}:
 [0x00, 0x00, 0x00]
 [0x00, 0x00, 0x00]
 [0x00, 0x00, 0x00]

julia> spi_transfer!(1, tx_buf, rx_buf)
9

julia> rx_buf
3-element Array{Array{UInt8,1},1}:
 [0x00, 0x01, 0xef]
 [0xef, 0x00, 0x00]
 [0x00, 0x00, 0x00]
spi_transfer(devid, tx_buf; kwargs...)

Execute a full duplex transfer to SPI device devid. devid is the ID of the SPI device considering the initialization order when the function init_spi was called.

tx_buf can be a vector of Integer, in which only one message will be sent, or a vector of vectors of Integer, in which multiple messages will be sent.

The result is returned in an object with the same type of tx_buf together with the number of words received.

The same keywords of spi_transfer! can be used.

julia> tx_buf = [0x01, 0x80, 0x00]
3-element Array{UInt8,1}:
 0x01
 0x80
 0x00

julia> spi_transfer(1, tx_buf)
(UInt8[0x00, 0x01, 0xf1], 3)

julia> spi_transfer(1, tx_buf)
(UInt8[0x00, 0x01, 0xf1], 3)

julia> tx_buf = [ [0x01, 0x80, 0x00] for i = 1:3 ]
3-element Array{Array{UInt8,1},1}:
 [0x01, 0x80, 0x00]
 [0x01, 0x80, 0x00]
 [0x01, 0x80, 0x00]

julia> spi_transfer(1, tx_buf)
(Array{UInt8,1}[[0x00, 0x01, 0xf2], [0x9f, 0x00, 0x00], [0x00, 0x00, 0x00]], 9)

Example

See the example Temperature.