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| 版本 | 日期 | 作者 | 说明 |
|---|---|---|---|
| V1 | 2020 | 韦东山 | 韦东山鸿蒙系统开发教程 |
>>>视频教程在线观看<<<：
https://www.100ask.net/detail/p_5fcf586ae4b04db7c0939c82/8
1. 基础知识
移植内核对技术的要求比较全面、比较细致。
1.1 单片机相关的知识
-
栈的作用
-
加载地址、链接地址
-
重定位
-
几个简单的硬件知识
- 串口
- 定时器
-
中断的概念
1.2 Linux操作相关的知识
- Linux常用命令
- 简单的脚本：脚本就是把命令写在一个文件里
- GCC编译命令
- Kconfig和Makefile
1.3 芯片相关知识
-
能阅读芯片手册(英文)
- 移植最小系统时，涉及的手册内容不多
-
能看懂硬件原理图
- 移植最小系统时，涉及的原理图内容不多
2. 驱动程序知识
对于只有单片机知识的人来说，怎么去操作硬件？
- 直接读写寄存器
- 使用库函数
在RTOS中，本质也是去读写寄存器，但是需要有统一的驱动程序框架。
所以：RTOS驱动 = 驱动框架 + 硬件操作
2.1 以点灯为例
2.1.1 硬件原理
2.1.2 单片机点灯
-
方法1：直接读写寄存器
-
方法2：使用厂家的HAL库
2.1.5 Liteos-a/Linux怎么点灯
使用MMU时，一般APP与内核是相互隔离的。APP通过标准的open/read/write等文件操作函数去调用驱动程序。
如下图所示：
为何要多此一举？
- 它们支持MMU(内存管理单元)
- 用户程序跟内核是分隔开的，用户程序不能直接读写寄存器
- 用户程序通过标准接口访问驱动程序
- 基于这些内核的软件一般都比单片机软件复杂，术业有专攻
- 不应该让写APP的人去看原理图、写驱动、写寄存器
- 软件和硬件隔离，硬件再怎么变化，只需要改驱动，APP不需要改
2.2 怎么编写驱动程序
2.2.1 驱动程序的核心
Linux和Liteos-a的驱动程序时类似的，Liteos-a的更加精简。
既然APP使用驱动是调用open/read/write等接口，
那么写驱动程序是最简单的方法就是提供对应的drv_open/drv_read/drv_write等函数。
这些函数放在一个结构体里：Linux对应file_operations结构体，Liteos-a对应file_operations_vfs结构体。
1. Linux
Linux中是定义一个file_operations结构体，如下:
struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, loff_t, loff_t, int datasync);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
int (*setlease)(struct file *, long, struct file_lock **);
long (*fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
int (*show_fdinfo)(struct seq_file *m, struct file *f);
};
2. Liteos-a
Liteos-a中定义了一个file_operations_vfs结构体，如下：
struct file_operations_vfs
{
/* The device driver open method differs from the mountpoint open method */
int (*open)(FAR struct file *filep);
/* The following methods must be identical in signature and position because
* the struct file_operations and struct mountp_operations are treated like
* unions.
*/
int (*close)(FAR struct file *filep);
ssize_t (*read)(FAR struct file *filep, FAR char *buffer, size_t buflen);
ssize_t (*write)(FAR struct file *filep, FAR const char *buffer, size_t buflen);
off_t (*seek)(FAR struct file *filep, off_t offset, int whence);
int (*ioctl)(FAR struct file *filep, int cmd, unsigned long arg);
int (*mmap)(FAR struct file* filep, struct VmMapRegion *region);
/* The two structures need not be common after this point */
#ifndef CONFIG_DISABLE_POLL
int (*poll)(FAR struct file *filep, poll_table *fds);
#endif
int (*unlink)(FAR struct inode *inode);
};
2.3 注册驱动程序
1. Linux
static struct file_operations hello_drv = {
.owner = THIS_MODULE,
.open = hello_drv_open,
.read = hello_drv_read,
.write = hello_drv_write,
.release = hello_drv_close,
};
int major = register_chrdev(0, "hello", &hello_drv); /* /dev/hello */
static struct class *hello_class = class_create(THIS_MODULE, "hello_class");
device_create(hello_class, NULL, MKDEV(major, 0), NULL, "hello"); /* /dev/hello */
2. Liteos-a
static const struct file_operations_vfs g_helloDevOps = {
.open = hello_open,
.close = hello_close,
.read = hello_read,
.write = NULL,
.seek = NULL,
.ioctl = NULL,
.mmap = NULL,
.unlink = NULL,
};
int ret = register_driver("/dev/hello", &g_helloDevOps, 0666, NULL);
2.4 APP如何使用
Linux和Liteos-a在APP层面都一样：
int main(int argc, char **argv)
{
int fd;
char buf[1024];
int len;
/* 1. 判断参数 */
if (argc < 2)
{
printf("Usage: %s -w <string>\n", argv[0]);
printf(" %s -r\n", argv[0]);
return -1;
}
/* 2. 打开文件 */
fd = open("/dev/hello", O_RDWR);
if (fd == -1)
{
printf("can not open file /dev/hello\n");
return -1;
}
/* 3. 写文件或读文件 */
if ((0 == strcmp(argv[1], "-w")) && (argc == 3))
{
len = strlen(argv[2]) + 1;
len = len < 1024 ? len : 1024;
write(fd, argv[2], len);
}
else
{
len = read(fd, buf, 1024);
buf[1023] = '\0';
printf("APP read : %s\n", buf);
}
close(fd);
return 0;
}
en = strlen(argv[2]) + 1;
len = len < 1024 ? len : 1024;
write(fd, argv[2], len);
}
else
{
len = read(fd, buf, 1024);
buf[1023] = ‘\0’;
printf(“APP read : %s\n”, buf);
}
close(fd);
return 0;
}
转载：https://blog.csdn.net/thisway_diy/article/details/110919590
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