linux设备驱动中ADC的使用

内核源代码arch\arm\plat-s3c24xx\s3c2410-clock.c

/* standard clock definitions */

static struct clk init_clocks_off[] = {
{
.name = "nand",
.id = -1,
.parent = &clk_h,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_NAND,
}, {
.name = "sdi",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_SDI,
}, {
.name = "adc",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_ADC,
}, {
.name = "i2c",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_IIC,
}, {
.name = "iis",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_IIS,
}, {
.name = "spi",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_SPI,
}
};

static struct clk init_clocks[] = {
{
.name = "lcd",
.id = -1,
.parent = &clk_h,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_LCDC,
}, {
.name = "gpio",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_GPIO,
}, {
.name = "usb-host",
.id = -1,
.parent = &clk_h,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_USBH,
}, {
.name = "usb-device",
.id = -1,
.parent = &clk_h,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_USBD,
}, {
.name = "timers",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_PWMT,
}, {
.name = "uart",
.id = 0,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_UART0,
}, {
.name = "uart",
.id = 1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_UART1,
}, {
.name = "uart",
.id = 2,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_UART2,
}, {
.name = "rtc",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_RTC,
}, {
.name = "watchdog",
.id = -1,
.parent = &clk_p,
.ctrlbit = 0,
}, {
.name = "usb-bus-host",
.id = -1,
.parent = &clk_usb_bus,
}, {
.name = "usb-bus-gadget",
.id = -1,
.parent = &clk_usb_bus,
},
};

从这里我们可以看到系统启动时，那些时钟使能了，那些被禁止了，所以我们的ADC时钟在系统启动后是不能使用的。
要使用ADC时钟首先我们需要获得ADC时钟，然后使能它。

获得时钟函数

struct clk *clk_get(struct device *dev, const char *id)

第一个参数中，因为clk->id一般为-1，所以直接传入NULL就可以了。

如果clk->id不为-1，函数会通过第一个参数传入的dev获取dev->bus_id。

第二个参数是一个字符串，用来指定你要获取的时钟的名字。参数传入后，内核查找到一个dev->id(或者-1)是否与clk->id一致，并且con_id与clk->name一致的时钟，如果不一致就会获取失败。所以，我这里的函数应该是：clk_get(NULL,
“adc”)。

使能时钟函数

int clk_enable(struct clk *clk)

禁止时钟函数

void clk_disable(struct clk *clk)

之后我们就可以使用ADC了。