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<H2>HiPi::Device::SPI</H2><p>The HiPi::Device::SPI module provides access to the kernel driver for the SPI bus.</p>
<p>See : <A HREF="topic_spidev.htm">SPI Device Driver</A></p>
<p>Loading and configuring the kernel SPI driver is controlled by configuring the device tree in your /boot/config.txt file.</p>
<p>See : <A HREF="topic_device_tree.htm">Using the Device Tree</A></p>
<!--
<p>The settings for the SPI device can be controlled in the <A HREF="control_app_spi.htm">HiPi Control GUI</A>.</p>
-->
<p>The following interface modules use HiPi::Device::SPI as a backend and may contain code that helps with your own usage.</p>
<p><A HREF="mod_interface_mcp3004.htm">HiPi::Interface::MCP3004</A><br />
<A HREF="mod_interface_mcp3008.htm">HiPi::Interface::MCP3008</A><br />
<A HREF="mod_interface_mcp49xx.htm">HiPi::Interface::MCP49XX</A><br /></p>
<A HREF="mod_interface_mcp23S17.htm">HiPi::Interface::MCP23S17</A><br /></p>
<h2>Class Methods</h2>
<!--
<h5>HiPi::Device::SPI->load_modules( $forceunload );</h5>
<pre> Loads the kernel device driver modules for SPI
spi_bcm2708
spidev
When $forceunload is true, unloads the kernel modules
first if they are loaded (effectively forces a reload)
spidev is loaded with the current bufsiz
Of course, the user the script is running as must have
root permissions to load and unload kernel modules.</pre>
<h5>HiPi::Device::SPI->unload_modules();</h5>
<pre> Unloads the kernel device driver modules for SPI
spi_bcm2708
spidev
Of course, the user the script is running as must have
root permissions to load and unload kernel modules.</pre>
<h5>HiPi::Device::SPI->get_bufsiz();</h5>
<pre> Returns the current bufsiz of a loaded spidev
module. If the module is not loaded or the process
does not have root permissions, returns the current
default module setting for bufsiz.</pre>
<h5>HiPi::Device::SPI->set_bufsiz( $newsiz );</h5>
<pre> Sets the bufsiz option of the spidev module. Must
unload and load the kernel module to do this.
Of course, the user the script is running as must have
root permissions to load and unload kernel modules.</pre>
-->
<h5>HiPi::Device::SPI->get_device_list();</h5>
<pre> Returns an array containing the names of available
devices.
Will normally return ('/dev/spidev0.0', '/dev/spidev0.1')
</pre>
<h2>Object Constructor and Methods</h2>
<h5>my $dev = HiPi::Device::SPI->new();</h5>
<pre> 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)
</pre>
<h3>SPI Methods</h3>
<h5>my $result = $dev->transfer( $buffer );</h5>
<pre> 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) + $vals[2];
Use the code for HiPi::Interface::MCP3008 and HiPi::Interface::MCP23S17
as guides.</pre>
<h5>$dev->set_bus_mode( $mode );</h5>
<pre> $mode one of
SPI_MODE_0
SPI_MODE_1
SPI_MODE_2
SPI_MODE_3
You can import these constants into your namespace with:
use HiPi::Device::SPI qw( :spi );
The documentation for your SPI device should tell you which
modes it supports. Default mode is SPI_MODE_0.</pre>
<h5>$dev->set_bus_maxspeed( $speed );</h5>
<pre> $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.
</pre></FONT>
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