安装 WiringPi

根据官网的描述，

WiringPi is a GPIO access library written in C for the BCM2835 used in the Raspberry Pi.

简单理解，WiringPi 是一个用 C 写的控制 GPIO 的库。

$ git clone git://git.drogon.net/wiringPi
$ cd wiringPi
$ ./build

装完测试一下，可以看到类似下面的输出。

[email protected]:~ $ gpio readall
+-----+-----+---------+------+---+-Model B2-+---+------+---------+-----+-----+
| BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
|     |     |    3.3v |      |   |  1 || 2  |   |      | 5v      |     |     |
|   2 |   8 |   SDA.1 |   IN | 1 |  3 || 4  |   |      | 5V      |     |     |
|   3 |   9 |   SCL.1 |   IN | 1 |  5 || 6  |   |      | 0v      |     |     |
|   4 |   7 | GPIO. 7 |   IN | 1 |  7 || 8  | 1 | ALT0 | TxD     | 15  | 14  |
|     |     |      0v |      |   |  9 || 10 | 1 | ALT0 | RxD     | 16  | 15  |
|  17 |   0 | GPIO. 0 |  OUT | 0 | 11 || 12 | 0 | OUT  | GPIO. 1 | 1   | 18  |
|  27 |   2 | GPIO. 2 |  OUT | 0 | 13 || 14 |   |      | 0v      |     |     |
|  22 |   3 | GPIO. 3 |  OUT | 0 | 15 || 16 | 1 | OUT  | GPIO. 4 | 4   | 23  |
|     |     |    3.3v |      |   | 17 || 18 | 0 | IN   | GPIO. 5 | 5   | 24  |
|  10 |  12 |    MOSI |   IN | 0 | 19 || 20 |   |      | 0v      |     |     |
|   9 |  13 |    MISO |   IN | 0 | 21 || 22 | 0 | IN   | GPIO. 6 | 6   | 25  |
|  11 |  14 |    SCLK |   IN | 0 | 23 || 24 | 1 | IN   | CE0     | 10  | 8   |
|     |     |      0v |      |   | 25 || 26 | 1 | IN   | CE1     | 11  | 7   |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
|  28 |  17 | GPIO.17 |   IN | 0 | 51 || 52 | 0 | IN   | GPIO.18 | 18  | 29  |
|  30 |  19 | GPIO.19 |   IN | 0 | 53 || 54 | 0 | IN   | GPIO.20 | 20  | 31  |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
| BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
+-----+-----+---------+------+---+-Model B2-+---+------+---------+-----+-----+
[email protected]:~ $

找个例子

搜到这篇文章，贴出重要部分的截图。

模仿作者 GitHub 仓库中的三个例子，最终撸出的代码如下，其中，

取 IP 的代码，参考了这个答案
取 CPU 温度的代码，参考了这篇文章和这个答案

// monitor8544.c

#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/sysinfo.h>
#include "PCD8544.h"
#include <sys/types.h>
#include <ifaddrs.h>
#include <netinet/in.h>
#include <arpa/inet.h>

// interface name
#define ETH_NAME "eth0"
// cpu temperature file path
#define CPU_TEMPERATURE_FILE_PATH "/sys/class/thermal/thermal_zone0/temp"

// pin setup
const int SCLK = 0;
const int DIN = 1;
const int DC = 2;
int RST = 4;
int CS = 3;
// lcd contrast
const int LCD_CONTRAST = 50;
// screen refresh cycle time in milliseconds
const int SCREEN_REFRESH_CYCLE = 4000;
// string length
const int MAX_STRING_LENGTH = 40;

double cpuTemperature() {
    FILE *file;
    double t;
    file = fopen(CPU_TEMPERATURE_FILE_PATH, "r");
    if (file == NULL) {
        fprintf(stderr, "Open file thermal_zone0/temp ERROR\n");
        return -1;
    }
    fscanf(file, "%lf", &t);
    fclose (file);
    return t / 1000;
}

void getIPv4Address(char (*address)[MAX_STRING_LENGTH]) {
    struct ifaddrs *ifAddrStruct = NULL, *ifa = NULL;
    void *tmpAddrPtr = NULL;
    strcpy(*address, "Link Down");
    getifaddrs(&ifAddrStruct);

    for (ifa = ifAddrStruct; ifa != NULL; ifa = ifa->ifa_next) {
        if (!ifa->ifa_addr) {
            continue;
        }
        if (ifa->ifa_addr->sa_family == AF_INET && !strcmp(ifa->ifa_name, ETH_NAME)) {
            tmpAddrPtr = &((struct sockaddr_in *)ifa->ifa_addr)->sin_addr;
            inet_ntop(AF_INET, tmpAddrPtr, *address, INET_ADDRSTRLEN);
        }
    }
    if (ifAddrStruct != NULL) {
        freeifaddrs(ifAddrStruct);
    }
}

int main() {
    if (wiringPiSetup() == -1) { // check wiringPi setup
        fprintf(stderr, "wiringPi Setup ERROR\n");
        exit(1);
    }
    LCDInit(SCLK, DIN, DC, CS, RST, LCD_CONTRAST);

    LCDclear();
    LCDshowLogo(); // show logo one time
    delay(SCREEN_REFRESH_CYCLE);

    while (1) {
        LCDclear();
        // network interface
        char network[MAX_STRING_LENGTH];
        getIPv4Address(&network);
        // system usage
        struct sysinfo sys_info;
        if (sysinfo(&sys_info) != 0) {
            fprintf(stderr, "Read sysinfo ERROR\n");
            return 2;
        }
        // uptime
        char uptimeInfo[MAX_STRING_LENGTH];
        sprintf(uptimeInfo, "UP  %.2lf h", 1.0 * sys_info.uptime / 3600);
        // cpu load and temperature
        char cpuInfo[MAX_STRING_LENGTH];
        sprintf(cpuInfo, "CPU %3ld%% %.1lf", sys_info.loads[0] / 1000, cpuTemperature());
        // ram usage
        char ramUsed[MAX_STRING_LENGTH];
        sprintf(ramUsed, "RAM %03ldM used", (sys_info.totalram - sys_info.freeram) / 1024 / 1024);
        char ramLeft[MAX_STRING_LENGTH];
        sprintf(ramLeft, "RAM %03ldM left", sys_info.freeram / 1024 / 1024);

        // build screen
        LCDdrawstring(0, 0, network);
        LCDdrawline(0, 10, 83, 10, BLACK);
        LCDdrawstring(0, 13, uptimeInfo);
        LCDdrawstring(0, 22, cpuInfo);
        LCDdrawstring(0, 31, ramUsed);
        LCDdrawstring(0, 40, ramLeft);
        LCDdisplay();
        delay(SCREEN_REFRESH_CYCLE);
    }
    return 0;
}

添加开机启动

直接在/etc/rc.local里加一句话：

sudo /full/path/to/your/executable/file &

不要少了最后的&，否则 Pi 无法启动。

If your command runs continuously (perhaps runs an infinite loop) or is likely not to exit, you must be sure to fork the process by adding an ampersand to the end of the command, like so:
python /home/pi/myscript.py &
Otherwise, the script will not end and the Pi will not boot. The ampersand allows the command to run in a separate process and continue booting with the process running.

花拳绣腿 & 柴米油盐

PCD8544 屏幕显示树莓派运行状态

安装 WiringPi

找个例子

添加开机启动