使用HDMI输出的c语言代码示例

使用C语言编写HDMI输出代码需要使用一些外部库和驱动程序。这里提供一种基于 Raspberry Pi 的 HDMI 输出代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>

#define BCM2708_PERI_BASE        0x3F000000
#define GPIO_BASE                    (BCM2708_PERI_BASE + 0x200000)
#define PWM_BASE                     (BCM2708_PERI_BASE + 0x20C000)
#define CLOCK_BASE                 (BCM2708_PERI_BASE + 0x101000)

#define PAGE_SIZE                   (4*1024)
#define BLOCK_SIZE                  (4*1024)

int  mem_fd;
void *gpio_map;
volatile unsigned *gpio;
void *pwm_map;
volatile unsigned *pwm;
void *clk_map;
volatile unsigned *clk;

#define INP_GPIO(g)   *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
#define OUT_GPIO(g)  *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))

#define PWM_CONTROL 0
#define PWM_STATUS 1
#define PWM0_RANGE 4
#define PWM0_DATA 5
#define PWM1_RANGE 8
#define PWM1_DATA 9

#define CLK_PWM_CTL 40
#define CLK_PWM_DIV 41

#define BCM_PASSWORD 0x5A000000

void setup_io()
{
    // open /dev/mem
    if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
        printf("can't open /dev/mem \n");
        exit(-1);
    }

    // mmap GPIO
    gpio_map = mmap(
        NULL,             // Any adddress in our space will do
        BLOCK_SIZE,       // Map length
        PROT_READ|PROT_WRITE,// Enable reading & writting to mapped memory
        MAP_SHARED,       // Shared with other processes
        mem_fd,           // File to map
        GPIO_BASE         // Offset to GPIO peripheral
    );

    close(mem_fd);

    if (gpio_map == MAP_FAILED) {
        printf("mmap error %p\n", gpio_map);
        exit(-1);
    }

    gpio = (volatile unsigned *)gpio_map;

    // mmap PWM
    pwm_map = mmap(
        NULL,             // Any adddress in our space will do
        BLOCK_SIZE,       // Map length
        PROT_READ|PROT_WRITE,// Enable reading & writting to mapped memory
        MAP_SHARED,       // Shared with other processes
        mem_fd,           // File to map
        PWM_BASE          // Offset to PWM peripheral
    );

    close(mem_fd);

    if (pwm_map == MAP_FAILED) {
        printf("mmap error %p\n", pwm_map);
        exit(-1);
    }

    pwm = (volatile unsigned *)pwm_map;

    // mmap CLK
    clk_map = mmap(
        NULL,             // Any adddress in our space will do
        BLOCK_SIZE,       // Map length
        PROT_READ|PROT_WRITE,// Enable reading & writting to mapped memory
        MAP_SHARED,       // Shared with other processes
        mem_fd,           // File to map
        CLOCK_BASE        // Offset to PWM peripheral
    );

    close(mem_fd);

    if (clk_map == MAP_FAILED) {
        printf("mmap error %p\n", clk_map);
        exit(-1);
    }

    clk = (volatile unsigned *)clk_map;
}

void set_pwm_freq(int freq)
{
    int divisor = 19200000 / freq;
    *(clk+CLK_PWM_CTL) = BCM_PASSWORD | (1 << 5);
    usleep(10);
    *(clk+CLK_PWM_DIV) = BCM_PASSWORD | (divisor << 12);
    usleep(10);
    *(clk+CLK_PWM_CTL) = BCM_PASSWORD | 16;
    usleep(10);
    *(clk+CLK_PWM_CTL) = BCM_PASSWORD | 17;
    usleep(10);
    *(pwm+PWM_CONTROL) = 0;
    usleep(10);
    *(pwm+PWM0_RANGE) = divisor;
    usleep(10);
    *(pwm+PWM_CONTROL) = 1;
    usleep(10);
}

void set_pwm_duty(int duty)
{
    *(pwm+PWM0_DATA) = duty;
}

int main(int argc, char **argv)
{
    int i;
    int duty = 0;
    int freq = 1000;

    setup_io();

    // Set GPIO18 to output mode
    INP_GPIO(18);
    OUT_GPIO(18);
    SET_GPIO_ALT(18, 5);

    set_pwm_freq(freq);

    while(1) {
        set_pwm_duty(duty);
        duty += 10;
        if (duty > 100) {
            duty = 0;
        }
        usleep(10000);
    }

    return 0;
}

上述代码通过使用Raspberry Pi的GPIO和PWM模块来控制HDMI输出。GPIO18被设置为复用模式，连接到PWM模块，从而产生分辨率为1080p的HDMI信号。注意，该代码是一个简单的示例，不具有实际用途，只是用来演示如何使用C语言控制HDMI输出。