marcelaraujo/php_spi

An OO PHP interface to SPI devices developed for use on the Raspberry Pi

This is a standalone PHP extension for accessing SPI on Linux systems. This has been developed solely for my RaspberryPi, but it should run on any Unix like system with SPI hardware enabled.

My inspiration for building this is the Light Painting project on AdaFruit. I want to build a similar device, but I want to be able to leverage my existing PHP skills rather than feel my way around another language. Please check the examples folder for a PHP script for driving the display in the same way that they have done with Python.

BUILDING

To be able to build PHP extensions you will need to have the dev package installed:

$ sudo apt-get install php5-dev

To compile your new extension, you will have to execute the following steps:

$ ./phpize
$ ./configure --enable--spi
$ make
$ make test
$ sudo make install

TESTING

You can now load the extension using a php.ini directive

extension="spi.so"

or load it at runtime using the dl() function

dl("spi.so");

The extension should now be available, you can test this using the extension_loaded() function:

if (extension_loaded("spi"))
    echo "spi loaded :)";
else
    echo "something is wrong :(";

The extension will also add its own block to the output of phpinfo();

USAGE

You may find that by default that you need to run any SPI scripts as root, to fix this you need to:

sudo chmod 666 /dev/spidev*

You can fix this permanently adding this to your /etc/rc.local:

chmod 666 /dev/spidev*

The setupTimer/usecDelay methods make use of /dev/mem and therefore will always need root access to run.

To access an SPI interface, you need to instantiate an Spi object:

/**
 * First argument is the bus, always 0 on a Raspberry Pi
 * Second argument is the chipselect, either 0 or 1 on a Raspberry Pi
 * Third argument is an associate array of the following options:
 * "mode": The SPI mode constant - SPI_MODE_0..3
 * "bits": How many bits per word
 * "speed": The bus speed in Hz
 * "delay": Delay between bit sending
 *
 * The default values are shown in this example
 */
$spi = new Spi(0, 0, array(
    'mode'  => SPI_MODE_0,
    'bits'  => 8,
    'speed' => 1000000,
    'delay' => 0
));

However, if you are OK with the default values, all you need to do is supply the bus and chipselect parameters:

$spi = new Spi(0, 1);

Once you are connected to the SPI device, you can then transfer data as follows:

$data = array(
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0x40, 0x00, 0x00, 0x00, 0x00, 0x95,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xDE, 0xAD, 0xBE, 0xEF, 0xBA, 0xAD,
    0xF0, 0x0D,
);
$data = $spi->transfer($data);
var_dump($data);

Data is sent full-duplex, so if you connect your MOSI and MISO pins to each other (GPIO pins 9 and 10) the data received will exactly match the data sent.

Whilst my tests reveal that no method for timing is ever going to be truly reliable I have implemented a timer based on code I found for this Magic Wand project. It works based on a free-running timer on the BCM2835 chip, the delay code is very crude, and will peg your CPU at 100% whilst running, but it does to seem work more accurately than usleep() most of the time.

To send blocks of data in sequence to the SPI bus, you can use the blockTransfer method. This takes an array of arrays of 'columns' of data and sends each column in sequence with a user-specified delay in milliseconds (as the optional second argument, default is 1 millisecond). As this method has been developed primarily for sending data to a string of LEDs, there is an optional 3rd parameter which when set to true discards the data read from the SPI bus and simply returns the number of bytes sent.

This is an alpha release, please report any issues you experience :o)