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#include
#include
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#include
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#include
#include
#include
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#include
#define DEVICE_NAME "pwm"
#define PWM_IOCTL_SET_FREQ 1 //设置pwm的频率
#define PWM_IOCTL_STOP 0 //停止pwm
static struct semaphore lock;
//定义信号量，此处的信号量是一个互斥信号量，用于PWM设备之多只能被一个进程打开
/* freq: pclk/50/16/65536 ~ pclk/50/16
* if pclk = 50MHz, freq is 1Hz to 62500Hz
* human ear : 20Hz~ 20000Hz
*/
static void PWM_Set_Freq( unsigned long freq )
{
unsigned long tcon;
unsigned long tcnt;
unsigned long tcfg1;
unsigned long tcfg0;
struct clk *clk_p;
unsigned long pclk;
//set GPB0 as tout0, pwm output
s3c2410_gpio_cfgpin(S3C2410_GPB(0), S3C2410_GPB0_TOUT0);//功能配置
tcon = __raw_readl(S3C2410_TCON); //获得定时器控制寄存器的数值
tcfg1 = __raw_readl(S3C2410_TCFG1); //获得定时器配置寄存器0的值
tcfg0 = __raw_readl(S3C2410_TCFG0); //获得定时器配置寄存器1的值
//prescaler = 50
tcfg0 &= ~S3C2410_TCFG_PRESCALER0_MASK;
tcfg0 |= (50 - 1);
//mux = 1/16
tcfg1 &= ~S3C2410_TCFG1_MUX0_MASK;
tcfg1 |= S3C2410_TCFG1_MUX0_DIV16;
__raw_writel(tcfg1, S3C2410_TCFG1);
__raw_writel(tcfg0, S3C2410_TCFG0);
clk_p = clk_get(NULL, "pclk");
pclk = clk_get_rate(clk_p);
tcnt = (pclk/50/16)/freq;
__raw_writel(tcnt, S3C2410_TCNTB(0));
__raw_writel(tcnt/2, S3C2410_TCMPB(0));
tcon &= ~0x1f;
tcon |= 0xb; //disable deadzone, auto-reload, inv-off, update TCNTB0&TCMPB0, start timer 0
__raw_writel(tcon, S3C2410_TCON);
tcon &= ~2; //clear manual update bit
__raw_writel(tcon, S3C2410_TCON);
}
static void PWM_Stop(void)
{
s3c2410_gpio_cfgpin(S3C2410_GPB(0), S3C2410_GPIO_OUTPUT);
s3c2410_gpio_setpin(S3C2410_GPB(0), 0);
}
static int s3c24xx_pwm_open(struct inode *inode, struct file *file)
{
if (!down_trylock(&lock))//判断是否设备已经打开，已打开返回EBUSY
return 0;
else
return -EBUSY;
}
static int s3c24xx_pwm_close(struct inode *inode, struct file *file)
{
PWM_Stop();//停止PWM
up(&lock);//释放信号量
return 0;
}
static int s3c24xx_pwm_ioctl(struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg)
{
//printk("ioctl pwm: %x %lxn", cmd, arg);
switch (cmd) {
case PWM_IOCTL_SET_FREQ:
if (arg == 0)
return -EINVAL;
PWM_Set_Freq(arg);
break;
case PWM_IOCTL_STOP:
PWM_Stop();
break;
}
return 0;
}
static struct file_operations dev_fops = {
.owner = THIS_MODULE,
.open = s3c24xx_pwm_open,
.release = s3c24xx_pwm_close,
.ioctl = s3c24xx_pwm_ioctl,
};
static struct miscdevice misc = {
.minor = MISC_DYNAMIC_MINOR,
.name = DEVICE_NAME,
.fops = &dev_fops,
};
static int __init dev_init(void)
{
int ret;
init_MUTEX(&lock);
ret = misc_register(&misc);
printk (DEVICE_NAME"tinitializedn");
return ret;
}
static void __exit dev_exit(void)
{
misc_deregister(&misc);
}
module_init(dev_init);
module_exit(dev_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("FriendlyARM Inc.");
MODULE_DESCRIPTION("S3C2410/S3C2440 PWM Driver");
分析，这个程序的结构比较简单，只实现了open(),ioctl(),close()功能，其中最主要的就是ioctl()功能，在ioctl()中最重要的核心函数为static void PWM_Set_Freq( unsigned long freq )；所以说只要分析懂了这个函数，这个驱动也都全懂了。要是做过这个裸机程序的就更简单了。里面出现的一些没分析的，在本博客另一篇LED驱动分析中基本都说过了，不清楚的可以去看那个。
首先分析static void PWM_Set_Freq( unsigned long freq )；
static void PWM_Set_Freq( unsigned long freq )
{
unsigned long tcon;
unsigned long tcnt;
unsigned long tcfg1;
unsigned long tcfg0;
struct clk *clk_p;
unsigned long pclk;
//set GPB0 as tout0, pwm output
s3c2410_gpio_cfgpin(S3C2410_GPB(0), S3C2410_GPB0_TOUT0);//功能配置
tcon = __raw_readl(S3C2410_TCON); //获得定时器控制寄存器的数值
tcfg1 = __raw_readl(S3C2410_TCFG1); //获得定时器配置寄存器0的值
tcfg0 = __raw_readl(S3C2410_TCFG0); //获得定时器配置寄存器1的值
//prescaler = 50
tcfg0 &= ~S3C2410_TCFG_PRESCALER0_MASK;
tcfg0 |= (50 - 1);
//上面的两句是设置预分频器
//mux = 1/16
tcfg1 &= ~S3C2410_TCFG1_MUX0_MASK;
tcfg1 |= S3C2410_TCFG1_MUX0_DIV16;
//上面两句设置MUX0
__raw_writel(tcfg1, S3C2410_TCFG1);
__raw_writel(tcfg0, S3C2410_TCFG0);
//上面两句将配置好的数值写入到配置寄存器
clk_p = clk_get(NULL, "pclk");
pclk = clk_get_rate(clk_p);
//上面两句用于获取PCLK
tcnt = (pclk/50/16)/freq;
//上面这个数值决定了频率，
__raw_writel(tcnt, S3C2410_TCNTB(0));
__raw_writel(tcnt/2, S3C2410_TCMPB(0));
//上面两句将tcnt寄存器写入到TCNTB0，同时设置S3C2410_TCMPB0，也就是说占空比为50%
tcon &= ~0x1f; //低五位清零
tcon |= 0xb; //disable deadzone, auto-reload, inv-off, update TCNTB0&TCMPB0, start timer 0
__raw_writel(tcon, S3C2410_TCON);
tcon &= ~2; //clear manual update bit
__raw_writel(tcon, S3C2410_TCON);
}
看几个宏定义：
#define S3C2410_TCFG_PRESCALER0_MASK (255<<0) //0xff<<0
#define S3C2410_TCFG1_MUX0_MASK (15<<0) //0xf<<0
#define S3C2410_TCFG1_MUX0_DIV16 (3<<0)
分析：static void PWM_Stop(void)
static void PWM_Stop(void)
{
s3c2410_gpio_cfgpin(S3C2410_GPB(0), S3C2410_GPIO_OUTPUT);//配置管脚为输出状态
s3c2410_gpio_setpin(S3C2410_GPB(0), 0); //设置管脚为低电平输出
}
以下是测试程序
#include
#include
#include
#include
#define PWM_IOCTL_SET_FREQ 1
#define PWM_IOCTL_STOP 0
#define ESC_KEY 0x1b
static int getch(void)
{
struct termios oldt,newt;
int ch;
if (!isatty(STDIN_FILENO)) {
fprintf(stderr, "this problem should be run at a terminaln");
exit(1);
}
// save terminal setting
if(tcgetattr(STDIN_FILENO, &oldt) < 0) {
perror("save the terminal setting");
exit(1);
}
// set terminal as need