HiPi::Device::SPI
The HiPi::Device::SPI module provides access to the kernel driver for the SPI bus
Several of the HiPi Interface Modules are wrappers around HiPi::Device::SPI. You can use HiPi::Device::SPI directly to interface with other SPI peripherals.
Methods
- new
- transfer_byte_array
- transfer
- set_transfer_delay
- get_transfer_delay
- set_transfer_speed
- get_transfer_speed
- set_transfer_bitsperword
- get_transfer_bitsperword
- set_bus_mode
- get_bus_mode
- set_bus_maxspeed
- get_bus_maxspeed
Class Functions
Returns an instance of HiPi::Device::SPI.
my $dev = HiPi::Device::SPI->new();
There are a number of optional parameters you can pass to the constructor as shown below with their default values.
use HiPi qw( :spi );
my $dev = HiPi::Device::SPI->new(
devicename => '/dev/spidev0.0',
speed => SPI_SPEED_MHZ_1,
bitsperword => 8,
delay => 0,
);
devicename
The devicename gives the /dev/ file used by the SPI kernel driver. To connect to SPI 0 using the CEO cable select pin, use default devicename '/dev/spidev0.0'. To connect to SPI 0 using the CE1 pin, use default devicename '/dev/spidev0.1'.
speed
Set the speed in MHz of SPI transfers for this instance of HiPi::Device::SPI. This will override whatever the bus speed may be set at.
The default is 1000000 ( SPI_SPEED_MHZ_1 ). You can pass a numeric value or use one of the following constants.
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
bitsperword
You can set the bits per word for transfers using this instance of HiPi::Device::SPI. This will override whatever the global setting for the bus may be. Leave at the default of 8 unless you have some specific known requirement.
delay
You may set a delay in microseconds that is allowed to elapse at the end of the transer before the bus is released and the next transfer can start. Leave at the default of 0 unless you have some specific known requirement.
Transfer an array of bytes.
SPI transfers always write the same number of bytes as they read. If your SPI device requires you to write a register address or command to receive a 2 byte answer, you must write 3 bytes. One with the register address and two to receive the response.
my @writebites = ( $register, 0, 0 ); my @readbytes = $dev->transfer_byte_array( @writebytes ); # If the answer is a 16 bit number, MSB first, it is # in bytes 1 and 2 with byte 1 containing the MSB my $answer = ( $readbytes[1] << 8 ) + $readbytes[2];
Transfer a buffer. The method transfer_byte_array is a wrapper for this method and is simpler to use.
SPI transfers always write the same number of bytes as they read. If your SPI device requires you to write a register address or command to receive a 2 byte answer, you must write 3 bytes. One with the register address and two to receive the response.
my @writebites = ( $register, 0, 0 ); my $writebuffer = pack( 'C3', @writebites ); my $readbuffer = $dev->transfer( $writebuffer ); my @readbytes = unpack( 'C3', $readbuffer ); # If the answer is a 16 bit number, MSB first, it is # in bytes 1 and 2 with byte 1 containing the MSB my $answer = ( $readbytes[1] << 8 ) + $readbytes[2];
Set the value for delay ( as passed in the constructor ).
$dev->set_transfer_delay( 0 );
Get the current value for delay ( as passed in the constructor ).
my $val = $dev->get_transfer_delay;
Set the value for speed ( as passed in the constructor ).
$dev->set_transfer_speed( 1000_000 );
Get the current value for speed ( as passed in the constructor ).
my $val = $dev->get_transfer_speed;
Set the value for bitsperword ( as passed in the constructor ).
$dev->set_transfer_bitsperword( 8 );
Get the current value for bitsperword ( as passed in the constructor ).
my $val = $dev->get_transfer_bitsperword;
Set the mode for the SPI device. Global setting. Consult SPI documentation.
Use a mask of values:
SPI_CPHA SPI_CPOL SPI_MODE_0 SPI_MODE_1 SPI_MODE_2 SPI_MODE_3 SPI_CS_HIGH SPI_LSB_FIRST SPI_3WIRE SPI_LOOP SPI_NO_CS
$dev->set_bus_mode( $mask );
Get the current bus mode. Returns a mask of the values:
SPI_CPHA SPI_CPOL SPI_MODE_0 SPI_MODE_1 SPI_MODE_2 SPI_MODE_3 SPI_CS_HIGH SPI_LSB_FIRST SPI_3WIRE SPI_LOOP SPI_NO_CS
my $mask = $dev->get_bus_mode();
Set the maximum speed for the bus. Global setting. This can be overridden in any instance by the value for speed as set in the constructor or using method set_transfer_speed.
$dev->set_bus_maxspeed( SPI_SPEED_MHZ_1 );
Get the global maximum SPI bus speed. ( This can be overridden in any instance by the value for speed as set in the constructor or using method set_transfer_speed. )
my $speed = $dev->get_bus_maxspeed;
Returns an array containing the names of available devices.
For example ('/dev/spidev0.0', '/dev/spidev0.1').
my @devnames = HiPi::Device::SPI->get_device_list();