How to use PHP and SPI protocols for peripheral communication

1. Introduction
In recent years, with the rapid development of Internet of Things technology, peripheral communication has become more and more important. Among them, the SPI (Serial Peripheral Interface) protocol, as a common peripheral communication protocol, is widely used in various embedded systems. This article will introduce how to use PHP language and SPI protocol for peripheral communication, and attach code examples.

2. Introduction to SPI protocol
SPI (Serial Peripheral Interface) is a synchronous serial communication protocol, which is used to communicate between chips. The SPI protocol is relatively flexible in application and can connect multiple peripherals or connect to one peripheral through multiple master devices.

The communication method of the SPI protocol is full-duplex, that is, data can be sent and received at the same time. There is a master device (Master) and one or more slave devices (Slave) in communication. The master device controls the timing of communication, sends control commands and data to the slave device, and receives data returned from the slave device.

3. Implementation of PHP and SPI protocol communication
PHP is a commonly used server scripting language and is widely used in Web development. Although the PHP language itself does not directly support SPI communication, communication with hardware can be achieved by calling system commands or calling the underlying C library. The following will introduce two methods of PHP and SPI protocol communication.

1. How to call system commands
   A relatively simple method is to call system commands through PHP to communicate with the SPI device. This method is suitable for simple SPI communication scenarios.

// Execute the shell command for SPI communication
$command = "spi_communicate -s 100 -c 0x01";
$result = shell_exec($command );

// Process the return result
if ($result) {
// Parse the return result
// ...
echo "Communication successful!";
} else {
echo "Communication failed!";
}
?>

In the above code, we call a shell command named "spi_communicate" through the shell_exec function , transfer the setting parameters and control commands of SPI communication through command line parameters. The command execution results are saved in the $result variable, and further processing can be performed based on the results.

2. Call the underlying C library method
   Another more efficient and flexible method is to call the underlying C library through PHP to implement SPI communication. In this way, you can write C code yourself to implement the SPI initialization and communication process, and then call the compiled dynamic link library through PHP.

First, we write a C function to implement SPI communication:

include

include

include

include

include

include

include

int spi_communicate(uint32_t speed, uint8_t command) {
int ret = 0;
int fd = open( "/dev/spidev0.0", O_RDWR);
if (fd < 0) {

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}

close(fd);
return 0;
}

Then, we compile the above C code into the dynamic link library spi_comm .so:

$ gcc -shared -o spi_comm.so spi_comm.c

Finally, we call the dynamic link library in the PHP code:

// Call spi_comm.so dynamic link library
$spi = new FFI("spi_comm.so");

// Call C function to implement SPI communication
$result = $spi- >spi_communicate(100, 0x01);

// Process the return result
if ($result === 0) {
echo "Communication successful! ";
} else {
echo "Communication failed! ";
}
?>

In the above code, we use the FFI (Foreign Function Interface) extension library to call C functions. Through FFI, C functions can be loaded and called to achieve the same Interaction of the underlying C library.

4. Summary
This article introduces how to use PHP and SPI protocols to communicate with peripherals, including calling system commands and calling the underlying C library. These methods can be used. The PHP language implements control and communication of SPI devices, providing a more flexible choice for IoT application development. Through studying this article, I believe that readers will have a deeper understanding and mastery of PHP and SPI communication

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