[英]How to control the serial GPIO pin of Raspberry Pi via an Apache web sever
我想使用在Raspberry Pi上运行的Apache服务器通过GPIO串行端口将数据从Raspberry Pi发送到Arduino Uno 。 我将RPI的TX引脚连接到3.3 V至5 V电平转换器,并将其输出连接到RX Arduino PIN。
要将数据从Raspberry Pi发送到Arduino,我使用了为Raspberry Pi重新编译的以下C程序,它可以正常工作。 我将可执行代码重命名为SendUART
。
#include <stdio.h>
#include <unistd.h> //Used for UART
#include <fcntl.h> //Used for UART
#include <termios.h> //Used for UART
#include <string.h>
main(int argc,char **argv)
{
//----- TX BYTES -----
unsigned char tx_buffer[20];
unsigned char *p_tx_buffer;
int lx;
//-------------------------
//----- SETUP USART 0 -----
//-------------------------
//At bootup, pins 8 and 10 are already set to UART0_TXD, UART0_RXD (ie the alt0 function) respectively
int uart0_filestream = -1;
//OPEN THE UART
//The flags (defined in fcntl.h):
// Access modes (use 1 of these):
// O_RDONLY - Open for reading only.
// O_RDWR - Open for reading and writing.
// O_WRONLY - Open for writing only.
//
// O_NDELAY / O_NONBLOCK (same function) - Enables nonblocking mode. When set read requests on the file can return immediately with a failure status
// if there is no input immediately available (instead of blocking). Likewise, write requests can also return
// immediately with a failure status if the output can't be written immediately.
//
// O_NOCTTY - When set and path identifies a terminal device, open() shall not cause the terminal device to become the controlling terminal for the process.
uart0_filestream = open("/dev/ttyAMA0", O_RDWR | O_NOCTTY | O_NDELAY); //Open in non blocking read/write mode
if (uart0_filestream == -1)
{
//ERROR - CAN'T OPEN SERIAL PORT
printf("Error - Unable to open UART. Ensure it is not in use by another application\n");
}
//CONFIGURE THE UART
//The flags (defined in /usr/include/termios.h - see http://pubs.opengroup.org/onlinepubs/007908799/xsh/termios.h.html):
// Baud rate:- B1200, B2400, B4800, B9600, B19200, B38400, B57600, B115200, B230400, B460800, B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000, B2500000, B3000000, B3500000, B4000000
// CSIZE:- CS5, CS6, CS7, CS8
// CLOCAL - Ignore modem status lines
// CREAD - Enable receiver
// IGNPAR = Ignore characters with parity errors
// ICRNL - Map CR to NL on input (Use for ASCII comms where you want to auto correct end of line characters - don't use for bianry comms!)
// PARENB - Parity enable
// PARODD - Odd parity (else even)
struct termios options;
tcgetattr(uart0_filestream, &options);
options.c_cflag = B9600 | CS8 | CLOCAL | CREAD; //<Set baud rate
options.c_iflag = IGNPAR;
options.c_oflag = 0;
options.c_lflag = 0;
tcflush(uart0_filestream, TCIFLUSH);
tcsetattr(uart0_filestream, TCSANOW, &options);
p_tx_buffer = &tx_buffer[0];
strcpy(tx_buffer, argv[1]);
lx=strlen(tx_buffer);
if (uart0_filestream != -1)
{
int count = write(uart0_filestream, &tx_buffer[0], 10); //Filestream, bytes to write, number of bytes to write
if (count < 0)
{
printf("UART TX error\n");
}
}
//----- CLOSE THE UART -----
close(uart0_filestream);
}
然后,我使用了一个PHP脚本(test.php)通过“系统”命令来处理该软件:
<?php
$mes = "0123456789";
$retval = 0;
$last_line = 0;
echo($mes);
$SndMsg = "/var/www/SendUART " . $mes;
$last_line = system($SndMsg, $retval);
echo $last_line
?>
我通过命令行执行了它:
php -f test.php
该字符串已由Arduino正确接收(我为Arduino开发了一个简单的草图 ,如果从Rx引脚接收到所有字符,则会打开板载LED)。
然后,我通过Apache Web服务器调用了PHP脚本,并在地址栏中输入: http : //192.168.1.103/test.php
其中192.168.1.103是Raspberry Pi的IP地址,而test.php
是PHP脚本。 当然, test.php
和SenUART程序都存储在同一文件夹/ var / www /中,但是浏览器中显示以下错误:
0123456789错误-无法打开UART。 确保它未被其他应用程序使用
我该如何解决该问题?
运行您的Web服务器的用户可能无权访问UART。 您可以通过在httpd.conf
设置以下内容来配置Apache以root身份运行来快速测试:
User root
由于以root用户身份运行Web服务器不是一个好主意,因此,您需要找出Apache通常在系统上以何种身份运行的用户(可能是www
),并授予该用户使用串行端口的权限。 这样的事情可能会起作用:
chown :www /dev/ttyAMA0
chmod g+rw /dev/ttyAMA0
另外,您可能只需要将用户www
添加到类似callout
的组中:
useradd -G callout www
根据您的特定系统进行调整。
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