## HiPi::Device::SPI

The HiPi::Device::SPI module provides access to the kernel driver for the SPI bus.

See : SPI Device Driver

Loading and configuring the kernel SPI driver is controlled by configuring the device tree in your /boot/config.txt file.

See : Using the Device Tree

The following interface modules use HiPi::Device::SPI as a backend and may contain code that helps with your own usage.

HiPi::Interface::MCP3004
HiPi::Interface::MCP3008
HiPi::Interface::MCP49XX

HiPi::Interface::MCP23S17

## Class Methods

##### HiPi::Device::SPI->get_device_list();

        Returns an array containing the names of available
        devices.
        Will normally return ('/dev/spidev0.0', '/dev/spidev0.1')

## Object Constructor and Methods

##### my $dev = HiPi::Device::SPI->new();

        Returns a new instance of the HiPi::Device::SPI class.

        You can optionally specify several parameters as key
        value pairs in the constructor. Their default values
        are:

        my $dev = HiPi::Device::SPI->new(
            devicename   => '/dev/spidev0.0',
            speed        => SPI_SPEED_MHZ_1,
            bitsperword  => 8,
            delay        => 0,
        );

        In default setup mode the SPI driver for Raspberry Pi has two
        cable select pins assigned.

        For controlling a device connected to SPI0_CS0 you need
        devicename => '/dev/spidev0.0'

        For controlling a device connected to SPI0_CS1 you need
        devicename => '/dev/spidev0.1'

        You can control data transfer speed by specifying one of the
        following constants for the key value 'speed'

            SPI_SPEED_KHZ_500
            SPI_SPEED_MHZ_1
            SPI_SPEED_MHZ_2
            SPI_SPEED_MHZ_4
            SPI_SPEED_MHZ_8
            SPI_SPEED_MHZ_16
            SPI_SPEED_MHZ_32

        You can import these constants into your namespace with:

        use HiPi::Device::SPI qw( :spi );

        Consult SPI bus documentation if you find your devices need
        or would benefit from specifying none default values for
        'bitsperword' and 'delay'. (I haven't discovered a use for
        these)

### SPI Methods

##### my $result = $dev->transfer( $buffer );

        Writes $buffer to the connected SPI device and returns
        the length($buffer) bytes read. In SPI transfers the length
        of data returned is always the same as the length of data
        sent.

        Uses the speed, bitsperword and delay settings specified in
        the constructor.

        Depending on your device you will probably have to pack /
        unpack the $buffer and return value and engage in some
        bit shifting to retrieve the returned value.

        For example, your SPI device expects a transfer message of 4
        bytes in length.
        Arrange these 4 bytes on an array : @buffer.

        my @vals = unpack('C4',$spi->transfer(pack('C4',($addr,$reg,@buffer))));

        You will have to check the data sheets for your individual
        SPI device.

        For example, the MCP23S17 requires the first 2 bytes of a nessage
        to be a device address and a register address. It allows requests
        to retrieve any number of bytes.

        If I want to retrieve 10 bytes of information, I have to send 12
        bytes - 2 bytes of device and register address plus a 10 byte buffer.

        my @buffer = (0) x 10;
        my @vals = unpack('C12',$spi->transfer(pack('C12',($addr,$reg,@buffer))));

        The device doesn't populate $vals[0] or $vals[1] so the 10 bytes I
        read start at $vals[2];

        The MCP3008 analogue to digital converter uses 3 byte SPI transfers.
        In the request bytes the first byte and 4 high bits of the second byte
        define the request. The ADC returns its 10 bit result as the low 2 bits
        of the second byte + the third byte. In the request, we just send 0 as
        the third byte. Then we bitshift the value in the second byte.

        my @vals = unpack('C3',$spi->transfer(pack('C3',($byt1,$byt2,0))));
        my $result = (($vals[1] & 3) << 8) + $vals[2];

        Use the code for HiPi::Interface::MCP3008 and HiPi::Interface::MCP23S17
        as guides.

##### $dev->set_bus_mode( $mode );

        $mode   one of

            SPI_MODE_0
            SPI_MODE_1
            SPI_MODE_2
            SPI_MODE_3

        You can import these constants into your namespace with:

        use HiPi::Device::SPI qw( :spi );

        The documentation for your SPI device should tell you which
        modes it supports. Default mode is SPI_MODE_0.

##### $dev->set_bus_maxspeed( $speed );

        $speed   one of

            SPI_SPEED_KHZ_500
            SPI_SPEED_MHZ_1
            SPI_SPEED_MHZ_2
            SPI_SPEED_MHZ_4
            SPI_SPEED_MHZ_8
            SPI_SPEED_MHZ_16
            SPI_SPEED_MHZ_32

        You can import these constants into your namespace with:

        use HiPi::Device::SPI qw( :spi );

        I have not yet investigated how this setting combines with
        the speed setting specified in the constructor. The commands
        are simply wrappers for the exposed kernel device driver
        calls.

HiPi Modules Copyright © 2013 - 2016 Mark Dootson