嵌入式linux驱动-DMA笔记
一、开发环境
1、内核：Linux 2.6.22.6；
2、JZ2440v3
3、ubuntu 9.10
二、实现使用dma把一块数据存储到另一块上。实现过程：
1.创建字符设备驱动。包括定义file_operations结构变量，注册字符设备register_chrdev，使用class_create、class_device_create自动创建设备节点。
2.关于DMA的设置。
（1）分配中断。如：request_irq(IRQ_DMA3, s3c_dma_irq, 0, "s3c_dma", 1)。编写中断函数。
（2）分配源、目的缓冲区。
/* 分配SRC, DST对应的缓冲区 */
src = dma_alloc_writecombine(NULL, BUF_SIZE, &src_phys, GFP_KERNEL);
dst = dma_alloc_writecombine(NULL, BUF_SIZE, &dst_phys, GFP_KERNEL);
（3）地址重映射。
dma_regs = ioremap(DMA3_BASE_ADDR, sizeof(struct s3c_dma_regs));
（4）设置ＤＭＡ的寄存器。
如： /* 把源,目的,长度告诉DMA */
dma_regs->disrc = src_phys; /* 源的物理地址 */
dma_regs->disrcc = (0<<1) | (0<<0); /* 源位于AHB总线, 源地址递增 */
dma_regs->didst = dst_phys; /* 目的的物理地址 */
dma_regs->didstc = (0<<2) | (0<<1) | (0<<0); /* 目的位于AHB总线, 目的地址递增 */
dma_regs->dcon = (1<<30)|(1<<29)|(0<<28)|(1<<27)|(0<<23)|(0<<20)|(BUF_SIZE<<0); /* 使能中断,单个传输,软件触发, */
/* 启动DMA */
dma_regs->dmasktrig = (1<<1) | (1<<0);
3.为实现使用dma把一块数据存储到另一块上。在启动DMA后，进入休眠。DMA传输完成会产生中断，再唤醒休眠。
三、完整程序
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define MEM_CPY_NO_DMA 0
#define MEM_CPY_DMA 1
#define BUF_SIZE (512*1024)
#define DMA0_BASE_ADDR 0x4B000000
#define DMA1_BASE_ADDR 0x4B000040
#define DMA2_BASE_ADDR 0x4B000080
#define DMA3_BASE_ADDR 0x4B0000C0
static DECLARE_WAIT_QUEUE_HEAD(dma_wq);
static volatile int condition=0;
struct s3c_dma_regs{
unsigned long disrc0;
unsigned long disrcc0;
unsigned long didst0;
unsigned long didstc0;
unsigned long dcon0;
unsigned long dstat0;
unsigned long dcsrc0;
unsigned long dcdst0;
unsigned long dmasktrig0;
};
static volatile struct s3c_dma_regs *dma_regs;
static char *src;
static u32 src_phys;
static char *dst;
static u32 dst_phys;
static int major=0;
static struct class *class;
static int s3c_dma_ioctl (struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg)
{
int i;
memset(src, 0xaa, BUF_SIZE);
memset(dst, 0x55, BUF_SIZE);
switch(cmd)
{
case MEM_CPY_NO_DMA:
{
for(i=0;idisrc0=src_phys;
dma_regs->disrcc0=(0<<1)|(0<<0);
dma_regs->didst0 =dst_phys;
dma_regs->didstc0=(0<<2)|(0<<1)|(0<<0);
dma_regs->didstc0=(1<<29)|(0<<28)|(0<<23)|(0<<21)|(BUF_SIZE<<19);
//启动DMA
dma_regs->dmasktrig0=(1<<1)|(1<<0);
//如何知道什么时候完成传输
//休眠
wait_event_interruptible(dma_wq, condition);
if(memcmp(src, dst, BUF_SIZE)==0)
{
printk("MEM_CPY_DMA ok\n");
}
else
{
printk("MEM_CPY_DMA erro\n");
}
break;
}
}
return 0;
}
static struct file_operations dma_fops={
.owner=THIS_MODULE,
.ioctl =s3c_dma_ioctl,
};
static irqreturn_t s3c_dma_irq(int irq, void *devid)
{
condition=1;
//唤醒
wake_up_interruptible(&dma_wq);
return IRQ_HANDLED;
}
static int s3c_dma_init(void)
{
if(request_irq(IRQ_DMA3, s3c_dma_irq, 0,"s3c_dma",1))
{
free_irq(IRQ_DMA3, 1);
printk("can't request irq for dma \n");
return -ENOMEM;
}
//分配缓冲区
src=dma_alloc_writecombine(NULL,BUF_SIZE, &src_phys, GFP_KERNEL);
if(src==NULL)
{
dma_free_writecombine(NULL,BUF_SIZE, src,src_phys);
printk("can't alloc buffer for src \n");
return -ENOMEM;
}
dst=dma_alloc_writecombine(NULL,BUF_SIZE, &dst_phys, GFP_KERNEL);
if(dst==NULL)
{
dma_free_writecombine(NULL,BUF_SIZE, dst,dst_phys);
printk("can't alloc buffer for dst \n");
return -ENOMEM;
}
major=register_chrdev(0,"s3c_dma",&dma_fops);
class=class_create(THIS_MODULE, "sc3_dma");
class_device_create(class,NULL,MKDEV(major, 0),NULL,"dma");
dma_regs=ioremap(DMA3_BASE_ADDR, sizeof(struct s3c_dma_regs));
return 0;
}
static void s3c_dma_exit(void)
{
iounmap(dma_regs);
class_device_destroy(class,MKDEV(major, 0));
class_destroy(class);
unregister_chrdev(major,"s3c_dma");
dma_free_writecombine(NULL,BUF_SIZE, src,src_phys);
dma_free_writecombine(NULL,BUF_SIZE, dst,dst_phys);
free_irq(IRQ_DMA3, 1);
}
module_init(s3c_dma_init);
module_exit(s3c_dma_exit);
MODULE_LICENSE("GPL");
四、测试程序
#include
#include
#include
#include
#include
#include
/* ./dma_test nodma
* ./dma_test dma
*/
#define MEM_CPY_NO_DMA 0
#define MEM_CPY_DMA 1
void print_usage(char *name)
{
printf("Usage:\n");
printf("%s \n", name);
}
int main(int argc, char **argv)
{
int fd;
if (argc != 2)
{
print_usage(argv[0]);
return -1;
}
fd = open("/dev/dma", O_RDWR);
if (fd < 0)
{
printf("can't open /dev/dma\n");
return -1;
}
if (strcmp(argv[1], "nodma") == 0)
{
while (1)
{
ioctl(fd, MEM_CPY_NO_DMA);
}
}
else if (strcmp(argv[1], "dma") == 0)
{
while (1)
{
ioctl(fd, MEM_CPY_DMA);
}
}
else
{
print_usage(argv[0]);
return -1;
}
return 0;
}
