分类: LINUX
2012-09-25 19:41:21
几乎每一种外设都是通过读写设备上的寄存器来进行的,通常包括控制寄存器、状态寄存器和数据寄存器三大类,外设的寄存器通常被连续地编址。根据CPU体系结构的不同,CPU对IO端口的编址方式有两种:
(1)I/O映射方式(I/O-mapped)
典型地,如X86处理器为外设专门实现了一个单独的地址空间,称为"I/O地址空间"或者"I/O端口空间",CPU通过专门的I/O指令(如X86的IN和OUT指令)来访问这一空间中的地址单元。
(2)内存映射方式(Memory-mapped)
RISC指令系统的CPU(如ARM、PowerPC等)通常只实现一个物理地址空间,外设I/O端口成为内存的一部分。此时,CPU可以象访问一个内存单元那样访问外设I/O端口,而不需要设立专门的外设I/O指令。
但是,这两者在硬件实现上的差异对于软件来说是完全透明的,驱动程序开发人员可以将内存映射方式的I/O端口和外设内存统一看作是"I/O内存"资源。
一般来说,在系统运行时,外设的I/O内存资源的物理地址是已知的,由硬件的设计决定。但是CPU通常并没有为这些已知的外设I/O内存资源的物理地址预定义虚拟地址范围,驱动程序并不能直接通过物理地址访问I/O内存资源,而必须将它们映射到核心虚地址空间内(通过页表),然后才能根据映射所得到的核心虚地址范围,通过访内指令访问这些I/O内存资源。Linux在io.h头文件中声明了函数ioremap(),用来将I/O内存资源的物理地址映射到核心虚地址空间(3GB-4GB)中,原型如下:
void * ioremap(unsigned long phys_addr, unsigned long size, unsigned long flags); |
void iounmap(void * addr); |
#define readb(addr) (*(volatile unsigned char *) __io_virt(addr)) #define readw(addr) (*(volatile unsigned short *) __io_virt(addr)) #define readl(addr) (*(volatile unsigned int *) __io_virt(addr)) #define writeb(b,addr) (*(volatile unsigned char *) __io_virt(addr) = (b)) #define writew(b,addr) (*(volatile unsigned short *) __io_virt(addr) = (b)) #define writel(b,addr) (*(volatile unsigned int *) __io_virt(addr) = (b)) #define memset_io(a,b,c) memset(__io_virt(a),(b),(c)) #define memcpy_fromio(a,b,c) memcpy((a),__io_virt(b),(c)) #define memcpy_toio(a,b,c) memcpy(__io_virt(a),(b),(c)) |
static void get_rtc_time(int alm, struct rtc_time *rtc_tm) { spin_lock_irq(&rtc_lock); if (alm == 1) { rtc_tm->tm_year = (unsigned char)ALMYEAR & Msk_RTCYEAR; rtc_tm->tm_mon = (unsigned char)ALMMON & Msk_RTCMON; rtc_tm->tm_mday = (unsigned char)ALMDAY & Msk_RTCDAY; rtc_tm->tm_hour = (unsigned char)ALMHOUR & Msk_RTCHOUR; rtc_tm->tm_min = (unsigned char)ALMMIN & Msk_RTCMIN; rtc_tm->tm_sec = (unsigned char)ALMSEC & Msk_RTCSEC; } else { read_rtc_bcd_time: rtc_tm->tm_year = (unsigned char)BCDYEAR & Msk_RTCYEAR; rtc_tm->tm_mon = (unsigned char)BCDMON & Msk_RTCMON; rtc_tm->tm_mday = (unsigned char)BCDDAY & Msk_RTCDAY; rtc_tm->tm_hour = (unsigned char)BCDHOUR & Msk_RTCHOUR; rtc_tm->tm_min = (unsigned char)BCDMIN & Msk_RTCMIN; rtc_tm->tm_sec = (unsigned char)BCDSEC & Msk_RTCSEC; if (rtc_tm->tm_sec == 0) { /* Re-read all BCD registers in case of BCDSEC is 0. See RTC section at the manual for more info. */ goto read_rtc_bcd_time; } } spin_unlock_irq(&rtc_lock); BCD_TO_BIN(rtc_tm->tm_year); BCD_TO_BIN(rtc_tm->tm_mon); BCD_TO_BIN(rtc_tm->tm_mday); BCD_TO_BIN(rtc_tm->tm_hour); BCD_TO_BIN(rtc_tm->tm_min); BCD_TO_BIN(rtc_tm->tm_sec); /* The epoch of tm_year is 1900 */ rtc_tm->tm_year += RTC_LEAP_YEAR - 1900; /* tm_mon starts at 0, but rtc month starts at 1 */ rtc_tm->tm_mon--; } |
#define ALMDAY bRTC(0x60) #define ALMMON bRTC(0x64) #define ALMYEAR bRTC(0x68) |
#define bRTC(Nb) __REG(0x57000000 + (Nb)) |
# define __REG(x) io_p2v(x) |
#define io_p2v(x) ((x) | 0xa0000000) |
# define __PREG(x) io_v2p(x) |
#define io_v2p(x) ((x) & ~0xa0000000) |
下面的程序在启动的时候保留一段内存,然后使用ioremap将它映射到内核虚拟空间,同时又用remap_page_range映射到用户虚拟空间,这样一来,内核和用户都能访问。如果在内核虚拟地址将这段内存初始化串"abcd",那么在用户虚拟地址能够读出来:
/************mmap_ioremap.c**************/ #include #include #include #include #include #include #include MODULE_PARM(mem_start, "i"); MODULE_PARM(mem_size, "i"); static int mem_start = 101, mem_size = 10; static char *reserve_virt_addr; static int major; int mmapdrv_open(struct inode *inode, struct file *file); int mmapdrv_release(struct inode *inode, struct file *file); int mmapdrv_mmap(struct file *file, struct vm_area_struct *vma); static struct file_operations mmapdrv_fops = { owner: THIS_MODULE, mmap: mmapdrv_mmap, open: mmapdrv_open, release: mmapdrv_release, }; int init_module(void) { if ((major = register_chrdev(0, "mmapdrv", &mmapdrv_fops)) < 0) { printk("mmapdrv: unable to register character device/n"); return ( - EIO); } printk("mmap device major = %d/n", major); printk("high memory physical address 0x%ldM/n", virt_to_phys(high_memory) / 1024 / 1024); reserve_virt_addr = ioremap(mem_start *1024 * 1024, mem_size *1024 * 1024); printk("reserve_virt_addr = 0x%lx/n", (unsigned long)reserve_virt_addr); if (reserve_virt_addr) { int i; for (i = 0; i < mem_size *1024 * 1024; i += 4) { reserve_virt_addr[i] = 'a'; reserve_virt_addr[i + 1] = 'b'; reserve_virt_addr[i + 2] = 'c'; reserve_virt_addr[i + 3] = 'd'; } } else { unregister_chrdev(major, "mmapdrv"); return - ENODEV; } return 0; } /* remove the module */ void cleanup_module(void) { if (reserve_virt_addr) iounmap(reserve_virt_addr); unregister_chrdev(major, "mmapdrv"); return ; } int mmapdrv_open(struct inode *inode, struct file *file) { MOD_INC_USE_COUNT; return (0); } int mmapdrv_release(struct inode *inode, struct file *file) { MOD_DEC_USE_COUNT; return (0); } int mmapdrv_mmap(struct file *file, struct vm_area_struct *vma) { unsigned long offset = vma->vm_pgoff << PAGE_SHIFT; unsigned long size = vma->vm_end - vma->vm_start; if (size > mem_size *1024 * 1024) { printk("size too big/n"); return ( - ENXIO); } offset = offset + mem_start * 1024 * 1024; /* we do not want to have this area swapped out, lock it */ vma->vm_flags |= VM_LOCKED; if (remap_page_range(vma, vma->vm_start, offset, size, PAGE_SHARED)) { printk("remap page range failed/n"); return - ENXIO; } return (0); } |
int remap_page_range(vma_area_struct *vma, unsigned long from, unsigned long to, unsigned long size, pgprot_tprot); |
(在内核驱动程序的初始化阶段,通过ioremap()将物理地址映射到内核虚拟空间;在驱动程序的mmap系统调用中,使用remap_page_range()将该块ROM映射到用户虚拟空间。这样内核空间和用户空间都能访问这段被映射后的虚拟地址。)