前天编写S3C24x0芯片的ADC驱动。其实很简单，参考别人的驱动，把以前的驱动模板改改就好了。可是写好后没使用成功。测来测去，最后发现对ADC的寄存器根本无法写入，只能读出。郁闷！！一开始以为是我用的赋值语句不对，参考我的驱动学习文档，试了一圈，问题依旧！郁闷了整整两天之后，在网上看到有人也遇到了2410的外设寄存器无法赋值的情况，最后发现是时钟问题。受此启发，我回想起了以前看的Linux的SPI驱动，里面有以下语句：
hw->clk = clk_get(&pdev->dev, 'spi');
if (IS_ERR(hw->clk)) {
dev_err(&pdev->dev, 'No clock for device
');
err = PTR_ERR(hw->clk);
goto err_no_clk;
}
/* for the moment, permanently enable the clock */
clk_enable(hw->clk);
当时也没怎么在意，后悔啊！之后我在DAC驱动上加了类似的语句，参考了别人的2410触摸屏驱动，将'spi'改为'adc' 。实验成功！
--------------------------------------------------------------------------------
三星的S3C24x0处理器为了实现低功耗，增加对外设的时钟和电源的管理。具体的内容请看芯片手册的《7. Clock & Power Management》这一章。虽然芯片启动时默认这些外设的时钟是使能的，但在Linux下，启动时为了节能考虑，将部分时钟关闭了。如果没有使能这些时钟，就会出现无法对外设寄存器写操作的情况。Linux中时钟使能部分的源码主要有：
/include/asm-arm/plat-s3c24xx/clock.h
/include/asm-arm/arch-s3c2410/regs-clock.h
/arch/arm/mach-s3c2410/clock.c
参考这些源码，就可以大致知道Linux是如何操作S3C24x0处理器的外设时钟的。
特别是/arch/arm/mach-s3c2410/clock.c中的以下数据对编程有所帮助：
/* standard clock definitions */
static struct clk init_clocks_disable[] = {
{
.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,
},
};
|
楼主
标题置顶
标题高亮
