利用DMA进行数据传输的例子

在用DMA进行数据操作时，无非就是对DMA进行相关的控制和一些寄存器的配置，下面是一个比较经典的DMA进行传输的例子：
#include 
#include 
#include 
#include 
#include 
#include "system.h"
#include "sys/alt_dma.h"
//#include "altear_avalon_dma.h"
#include "altera_avalon_dma_regs.h"
#include "sys/alt_irq.h"
//static volatile unsigned int *P_read_RAM=
//                                     (unsigned int *)(SRAM25616_0_BASE+0x100000);
unsigned int *P_read_RAM;                                      
static volatile unsigned int *P_write_RAM=
                                      (unsigned int *)(SRAM25616_0_BASE+0x500000);
                                      
void DMA_interrupts(void* context, alt_u32 id);
void init_dma(void);
void write_data(void);
/******************************************************************
*  Function: main
*
*  Purpose: Continually prints the menu and performs the actions
*           requested by the user.
* 
******************************************************************/
int main(void)
{
 init_dma();
 write_data();
 alt_irq_register(DMA_0_IRQ,0,DMA_interrupts);
 while(1)
 {
 ;
 }
  return (0);
}
//DMA传输设置
void init_dma(void)
{  
alt_irq_register(DMA_0_IRQ,0,DMA_interrupts); //注册DMA中断服务程序
IOWR_ALTERA_AVALON_DMA_CONTROL (DMA_0_BASE, 0);//清控制寄存器
IOWR_ALTERA_AVALON_DMA_STATUS (DMA_0_BASE, 0);//清状态寄存器
IOWR_ALTERA_AVALON_DMA_LENGTH (DMA_0_BASE, 200);//写入一次DMA传输的总数据长度
IOWR_ALTERA_AVALON_DMA_RADDRESS (DMA_0_BASE,(int)P_read_RAM);//DMA传输的目标地址
IOWR_ALTERA_AVALON_DMA_WADDRESS (DMA_0_BASE,(int)P_write_RAM);//DMA传输的源地址
IOWR_ALTERA_AVALON_DMA_CONTROL (DMA_0_BASE, 
                          ALTERA_AVALON_DMA_CONTROL_HW_MSK      | //半字传输
                          ALTERA_AVALON_DMA_CONTROL_GO_MSK        |//启动DMA
                         ALTERA_AVALON_DMA_CONTROL_I_EN_MSK      |//开中断
                 //        ALTERA_AVALON_DMA_CONTROL_WCON_MSK      |
              //            ALTERA_AVALON_DMA_CONTROL_WEEN_MSK      |
                         ALTERA_AVALON_DMA_CONTROL_LEEN_MSK
              );
}

//DMA中断服务程序
void DMA_interrupts(void* context, alt_u32 id)
{    
 // int i;
 // for(i=0;i<300;i++);
  int si=IORD_ALTERA_AVALON_DMA_STATUS (DMA_0_BASE);//读取状态寄存器
if(si&0x1)//判断是否传输完成，如果传输完成，重新设置DMA。
  {
   IOWR_ALTERA_AVALON_DMA_CONTROL (DMA_0_BASE, 0);
IOWR_ALTERA_AVALON_DMA_STATUS (DMA_0_BASE, 0);
 IOWR_ALTERA_AVALON_DMA_CONTROL (DMA_0_BASE, 0);
IOWR_ALTERA_AVALON_DMA_LENGTH (DMA_0_BASE, 200);
IOWR_ALTERA_AVALON_DMA_RADDRESS (DMA_0_BASE,(int)P_read_RAM);
IOWR_ALTERA_AVALON_DMA_WADDRESS (DMA_0_BASE,(int)P_write_RAM);
IOWR_ALTERA_AVALON_DMA_CONTROL (DMA_0_BASE, 
                          ALTERA_AVALON_DMA_CONTROL_HW_MSK      | 
                          ALTERA_AVALON_DMA_CONTROL_GO_MSK        |
                          ALTERA_AVALON_DMA_CONTROL_I_EN_MSK      |
                         ALTERA_AVALON_DMA_CONTROL_WCON_MSK      |
                   //       ALTERA_AVALON_DMA_CONTROL_WEEN_MSK      |
                          ALTERA_AVALON_DMA_CONTROL_LEEN_MSK
              );
  }
}
/////////////////
void write_data(void)
{
    unsigned int i;
    for(i=0;i<200;i++)
    {
        if(i<100)
        {
            P_read_RAM[i]=0xaaaaaaaa;
        }
        else
        {
          P_read_RAM[i]=0x55555555;
        }
    }
}