Linux下SRAM的读写

 

项目中需要用ARM与FPGA进行通信，通信方式是通过FPGA生成的SRAM作为数据的交换区，ARM9芯片为ATMEL的AT91SAM9260，采用Linux 2.6.19的内核，今天搞了一天，总算是读写成功，下面简要的说明一下。

       ARM中只有I/O内存的没有I/O端口，ARM9运行后默认是开启MMU的，Linux采用虚拟存储管理内存，具体的内存管理方式本文不作展开。所以要使用Linux访问外设必须要先进行内存映射。这里主要涉及两个函数：

Ø         Request_mem_region：该函数检查所需要转换的内存是否被占用，进行合法性检查，有些驱动中没有，个人认为安全性起见还是使用为妙。

Ø         Ioremap：该函数完成物理地址到虚拟地址的映射，映射后的地址才能被Linux内核使用。

下面给出代码：

驱动程序：

#include <linux/module.h>#include <linux/types.h>#include <linux/fs.h>#include <linux/types.h>#include <linux/kernel.h>#include <linux/init.h>#include <linux/platform_device.h>#include <linux/cdev.h>#include <linux/ioctl.h>#include <linux/gpio.h>#include <linux/mm.h>#include <linux/errno.h>#include <asm/arch/hardware.h>#include <asm/arch/gpio.h>#include <asm/uaccess.h>#include <linux/slab.h> /*for Kmalloc*/#include <asm/io.h>/*for virt_to_phys*/#include <asm/hardware.h>#include <asm/arch/at91_pio.h>#include <asm/arch/at91rm9200.h>/*for sram address and size*/#define SRAM0_PHYADDR 0x300000#define SRAM0_SIZE 0x1000  /*4K*/int sram_major = 242;int sram_open(struct inode *inode,struct file *filp);int sram_release(struct inode *inode,struct file *filp);int sram_release(struct inode *inode,struct file *filp);ssize_t sram_read(struct file *filp , char __user *buf ,size_t count,loff_t *f_pos);ssize_t sram_write(struct file *filp , char __user *buf ,size_t count,loff_t *f_pos);//int sram_mmap(struct file *filp, struct vm_area_struct *vma );//static void sram_setup_cdev(struct sram_dev *dev,int index);int sram_init(void);void sram_cleanup(void);MODULE_AUTHOR("Cun Tian Rui");MODULE_LICENSE("Dual BSD/GPL");struct sram_dev{struct cdev cdev;unsigned long startAddr;unsigned long size;char *mapPtr;}sram_dev;struct sram_dev *sramdevp;struct file_operations sram_fops = {    .owner = THIS_MODULE,   // .ioctl = sram_ioctl,    .open  = sram_open,    .release = sram_release,    .read = sram_read,    .write = sram_write,   // .mmap = sram_mmap};int sram_open(struct inode *inode,struct file *filp){    struct sram_dev *devp;    devp = container_of(inode->i_cdev,struct sram_dev,cdev);    filp->private_data = devp;        return 0;}int sram_release(struct inode *inode,struct file *filp){    return 0;    }ssize_t sram_read(struct file *filp , char __user *buf ,size_t count,loff_t *f_pos){unsigned long p = *f_pos;        struct sram_dev *devp = filp->private_data;printk("Driver read function running\n");printk("p is %d\n",p); if (p >= devp->size)  return -EINVAL; if (count > devp->size-p)  count = devp->size-p; printk("count is %d\n",count);         if (copy_to_user(buf, devp->mapPtr+p,count))  return -EFAULT;        *f_pos+= count; return count; } ssize_t sram_write(struct file *filp , char __user *buf ,size_t count,loff_t *f_pos){        unsigned long p = *f_pos;        printk("Driver write function running\n");        printk("p is %d\n",p);struct sram_dev *devp = filp->private_data;if (p >= devp->size)  return -EINVAL; if (count > devp->size-p)  count = devp->size-p;        printk("count is %d\n",count);   if (copy_from_user( devp->mapPtr+p,buf,count))  return -EFAULT; *f_pos += count; return count;}/*int sram_mmap(struct file *filp, struct vm_area_struct *vma ){unsigned long offset = vma->vm_pgoff<<PAGE_SHIFT; unsigned long size = vma->vm_end - vma->vm_start; if ( size > SRAM0_SIZE ) { printk("size too big\n"); return(-ENXIO); }         offset = offset + SRAM0_PHYADDR; vma->vm_flags |= VM_LOCKED; if ( remap_pfn_range(vma,vma->vm_start,offset,size,PAGE_SHARED)) { printk("remap page range failed\n"); return -ENXIO; } return(0); }*/int sram_init(void){    int result;    int err,ret;    int devno = MKDEV(sram_major,0);    dev_t dev = MKDEV(sram_major,0);    if(sram_major)    {                result = register_chrdev_region(dev,1,"SRAM0");    }    if(result < 0)    {        return result;    }    sramdevp = kmalloc(sizeof(struct sram_dev),GFP_KERNEL);    if(!sramdevp)    {        result = - ENOMEM;        goto fail_malloc;    }    memset(sramdevp,0,sizeof(struct sram_dev));    //sram_setup_cdev(sramdevp,0);        sramdevp->startAddr = SRAM0_PHYADDR;    sramdevp->size = SRAM0_SIZE;    ret = request_mem_region(SRAM0_PHYADDR, SRAM0_SIZE, "SRAM0 Region");    if(ret==NULL){printk("Request Memory Region Failed!\n");return -1;}    sramdevp->mapPtr = ioremap(SRAM0_PHYADDR,SRAM0_SIZE);    cdev_init(&sramdevp->cdev,&sram_fops);    sramdevp->cdev.owner = THIS_MODULE;    sramdevp->cdev.ops = &sram_fops;    err = cdev_add(&sramdevp->cdev,devno,1);    if(err)    {        printk(KERN_NOTICE "Error %d adding SRAM%d",err,0);    }        printk( "SRAM0_virt_addr = 0x%lx\n", (unsigned long)sramdevp->mapPtr );      return 0;    fail_malloc:unregister_chrdev_region(dev,sramdevp);kfree(sramdevp);    return result;    }void sram_cleanup(void){    cdev_del(&sramdevp->cdev);       iounmap(sramdevp->mapPtr);    kfree(sramdevp);    unregister_chrdev_region(MKDEV(sram_major,0),1);  }module_init(sram_init);module_exit(sram_cleanup);

 

写SRAM：

#include<sys/types.h>#include<sys/stat.h>#include<fcntl.h>#include<stdio.h>#include<linux/fs.h>#include<stdlib.h>#include<unistd.h>#define SRAM_DEV "/dev/SRAM0"int main(){  int fd;   char * data="ctrboss";   fd=open(SRAM_DEV,O_WRONLY);if(fd<0){  printf("Unable to open sram device %s\n",SRAM_DEV);  return 0;}  write(fd,data,sizeof(data));  close(fd);  return 1;} 

读SRAM：

#include<sys/types.h>#include<sys/stat.h>#include<fcntl.h>#include<stdio.h>#include<linux/fs.h>#include<stdlib.h>#include<unistd.h>#define SRAM_DEV "/dev/SRAM0"int main(){  int i,fd;  char data[6];  fd=open(SRAM_DEV,O_RDONLY);  if(fd<0)  {   printf("Unable to open sram device %s\n",SRAM_DEV);   return 0;  }  read(fd,data,sizeof(data));  printf("data is %x\n",data[0]);  printf("data is %x\n",data[1]);  printf("data is %x\n",data[2]);  printf("data is %x\n",data[3]);  printf("data is %x\n",data[4]);  printf("data is %x\n",data[5]);    printf("data is %c\n",data[0]);  printf("data is %c\n",data[1]);  printf("data is %c\n",data[2]);  printf("data is %c\n",data[3]);  printf("data is %c\n",data[4]);  printf("data is %c\n",data[5]);  close(fd);  return 1;}