電子發(fā)燒友App
應(yīng)用程序write函數(shù)的使用：
char *p = “hello,world”;?
write(fd, p, 12); //將數(shù)據(jù)寫(xiě)入到設(shè)備
底層驅(qū)動(dòng)write接口
struct file_operations { ssize_t (*write) (struct file *file, const char __user *buf, size_t count, loff_t *ppos);};write接口作用：用于寫(xiě)設(shè)備，將數(shù)據(jù)寫(xiě)入到設(shè)備中與應(yīng)用程序write的調(diào)用關(guān)系：應(yīng)用程序調(diào)用write->...->調(diào)用驅(qū)動(dòng)write接口參數(shù)：file:文件指針buf:保存用戶緩沖區(qū)的首地址(p),在驅(qū)動(dòng)程序中不能直接訪問(wèn)這個(gè)buf，如果驅(qū)動(dòng)程序要向從用戶空間將數(shù)據(jù)從buf拷貝到內(nèi)核空間，必須利用內(nèi)核提供的內(nèi)存拷貝函數(shù)count:用戶要寫(xiě)入的字節(jié)數(shù)，例如12字節(jié) ppos:保存寫(xiě)的位置信息，例如 獲取上一次的寫(xiě)位置： loff_t pos = *ppos; 假如這次成功寫(xiě)了12字節(jié)； 最后要更新寫(xiě)位置信息： *ppos = pos + 12;
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切記：對(duì)于write接口的第二個(gè)參數(shù)buf,這個(gè)buf指針保存的是用戶緩沖區(qū)的首地址，在內(nèi)核空間不能直接訪問(wèn)操作，需要利用內(nèi)核的內(nèi)存拷貝函數(shù)，將用戶數(shù)據(jù)拷貝到內(nèi)核空間，這個(gè)內(nèi)存拷貝函數(shù)：
unsigned long copy_from_user(void *to, void __user *from, unsigned long n)作用：將用戶緩沖區(qū)的數(shù)據(jù)拷貝到內(nèi)核緩沖區(qū)中參數(shù)：to:目的地址，傳遞內(nèi)核緩沖區(qū)的首地址from:源地址，傳遞用戶緩沖區(qū)的首地址(buf)n:要拷貝的字節(jié)數(shù)將來(lái)只要看到__user修飾的指針，就不能在驅(qū)動(dòng)中直接訪問(wèn)操作，必須利用內(nèi)存拷貝函數(shù)！
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案例：編寫(xiě)字符設(shè)備驅(qū)動(dòng)，提供write接口，將用戶空間的數(shù)據(jù)寫(xiě)入到內(nèi)核空間
int udata = 0x5555;? write(fd, &udata, sizeof(udata));
#include #include #include //struct file_operations#include //struct cdev + 設(shè)備號(hào)#include #include #include //copy_to_user//聲明描述LED硬件相關(guān)的數(shù)據(jù)結(jié)構(gòu)struct led_resource { char *name; int gpio;};//定義初始化LED硬件信息static struct led_resource led_info[] = { [0] = { .name = "LED1", .gpio = S5PV210_GPC0(3) }, [1] = { .name = "LED2", .gpio = S5PV210_GPC0(4) }};//定義設(shè)備號(hào)static dev_t dev;//定義字符設(shè)備對(duì)象static struct cdev led_cdev;//調(diào)用關(guān)系：應(yīng)用程序open->....->led_openstatic int led_open(struct inode *inode, struct file *file){ int i; for(i = 0; i < ARRAY_SIZE(led_info); i++) gpio_set_value(led_info[i].gpio, 1); printk("%s ", __func__); return 0; //執(zhí)行成功返回0，執(zhí)行失敗返回負(fù)值 }//調(diào)用關(guān)系：應(yīng)用程序close->...->led_closestatic int led_close(struct inode *inode, struct file *file){ int i; for(i = 0; i < ARRAY_SIZE(led_info); i++) gpio_set_value(led_info[i].gpio, 0); printk("%s ", __func__); return 0; //執(zhí)行成功返回0，執(zhí)行失敗返回負(fù)值 }//調(diào)用關(guān)系：應(yīng)用程序read->...->led_readstatic ssize_t led_read(struct file *file, char __user *buf, size_t count, loff_t *ppos){ //定義初始化內(nèi)核緩沖區(qū)(存儲(chǔ)空間再后1G虛擬內(nèi)存中) int kdata = 0x5555; //將內(nèi)核數(shù)據(jù)上報(bào)給用戶 //切記：buf雖然保存的用戶緩沖區(qū)的首地址，但不能直接訪問(wèn) //*(int *)buf = kdata;錯(cuò)誤 copy_to_user(buf, &kdata, sizeof(kdata)); printk("%s ", __func__); return sizeof(kdata); //失敗返回負(fù)值，成功返回實(shí)際讀取的字節(jié)數(shù)}//調(diào)用關(guān)系：應(yīng)用程序write->...->最終調(diào)用led_writestatic ssize_t led_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos){ //定義內(nèi)核緩沖區(qū) int kdata; //拷貝用戶數(shù)據(jù)到內(nèi)核 copy_from_user(&kdata, buf, sizeof(kdata)); printk("%s:從用戶寫(xiě)入的數(shù)據(jù) kdata = %#x ", __func__, kdata); return count; //失敗返回負(fù)值，成功返回寫(xiě)入的字節(jié)數(shù)}//定義初始化硬件操作方法static struct file_operations led_fops = { .owner = THIS_MODULE, .open = led_open, //打開(kāi)設(shè)備 .release = led_close, //關(guān)閉設(shè)備 .read = led_read, //讀取設(shè)備 .write = led_write //寫(xiě)設(shè)備};static int led_init(void){ int i; //申請(qǐng)?jiān)O(shè)備號(hào) alloc_chrdev_region(&dev, 0, 1, "tarena"); //初始化字符設(shè)備對(duì)象 cdev_init(&led_cdev, &led_fops); //注冊(cè)字符設(shè)備對(duì)象到內(nèi)核 cdev_add(&led_cdev, dev, 1); //申請(qǐng)GPIO資源和配置GPIO為輸出口，輸出0(省電) for (i = 0; i < ARRAY_SIZE(led_info); i++) { gpio_request(led_info[i].gpio, led_info[i].name); gpio_direction_output(led_info[i].gpio, 0); } return 0;}static void led_exit(void){ int i; //輸出0，釋放GPIO資源 for (i = 0; i < ARRAY_SIZE(led_info); i++) { gpio_set_value(led_info[i].gpio, 0); gpio_free(led_info[i].gpio); } //卸載字符設(shè)備對(duì)象 cdev_del(&led_cdev); //釋放設(shè)備號(hào) unregister_chrdev_region(dev, 1);}module_init(led_init);module_exit(led_exit);MODULE_LICENSE("GPL");
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#include #include #include #include int main(void){ int fd; int udata = 0x5555; //定義用戶緩沖區(qū) //打開(kāi)設(shè)備 //open->....->調(diào)用led_open fd = open("/dev/myled", O_RDWR); if (fd < 0) { printf("打開(kāi)設(shè)備失敗! "); return -1; } //write->...->調(diào)用led_write write(fd, &udata, sizeof(udata)); //關(guān)閉設(shè)備 //close->...->調(diào)用led_close close(fd); return 0;}
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案例：用戶寫(xiě)1，開(kāi)所有的燈；用戶寫(xiě)0，關(guān)所有的燈；
#include #include #include //struct file_operations#include //struct cdev + 設(shè)備號(hào)#include #include #include //copy_to_user//聲明描述LED硬件相關(guān)的數(shù)據(jù)結(jié)構(gòu)struct led_resource { char *name; int gpio;};//定義初始化LED硬件信息static struct led_resource led_info[] = { [0] = { .name = "LED1", .gpio = S5PV210_GPC0(3) }, [1] = { .name = "LED2", .gpio = S5PV210_GPC0(4) }};//定義設(shè)備號(hào)static dev_t dev;//定義字符設(shè)備對(duì)象static struct cdev led_cdev;//調(diào)用關(guān)系：應(yīng)用程序open->....->led_openstatic int led_open(struct inode *inode, struct file *file){ int i; for(i = 0; i < ARRAY_SIZE(led_info); i++) gpio_set_value(led_info[i].gpio, 1); printk("%s ", __func__); return 0; //執(zhí)行成功返回0，執(zhí)行失敗返回負(fù)值 }//調(diào)用關(guān)系：應(yīng)用程序close->...->led_closestatic int led_close(struct inode *inode, struct file *file){ int i; for(i = 0; i < ARRAY_SIZE(led_info); i++) gpio_set_value(led_info[i].gpio, 0); printk("%s ", __func__); return 0; //執(zhí)行成功返回0，執(zhí)行失敗返回負(fù)值 }//調(diào)用關(guān)系：應(yīng)用程序read->...->led_readstatic ssize_t led_read(struct file *file, char __user *buf, size_t count, loff_t *ppos){ //定義初始化內(nèi)核緩沖區(qū)(存儲(chǔ)空間再后1G虛擬內(nèi)存中) int kdata = 0x5555; //將內(nèi)核數(shù)據(jù)上報(bào)給用戶 //切記：buf雖然保存的用戶緩沖區(qū)的首地址，但不能直接訪問(wèn) //*(int *)buf = kdata;錯(cuò)誤 copy_to_user(buf, &kdata, sizeof(kdata)); printk("%s ", __func__); return sizeof(kdata); //失敗返回負(fù)值，成功返回實(shí)際讀取的字節(jié)數(shù)}//調(diào)用關(guān)系：應(yīng)用程序write->...->最終調(diào)用led_writestatic ssize_t led_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos){ int i; //定義內(nèi)核緩沖區(qū) int kdata; //拷貝用戶數(shù)據(jù)到內(nèi)核 copy_from_user(&kdata, buf, sizeof(kdata)); //開(kāi)或者關(guān)燈 for (i = 0; i < ARRAY_SIZE(led_info); i++) gpio_set_value(led_info[i].gpio, kdata); return count; //失敗返回負(fù)值，成功返回寫(xiě)入的字節(jié)數(shù)}//定義初始化硬件操作方法static struct file_operations led_fops = { .owner = THIS_MODULE, .open = led_open, //打開(kāi)設(shè)備 .release = led_close, //關(guān)閉設(shè)備 .read = led_read, //讀取設(shè)備 .write = led_write //寫(xiě)設(shè)備};static int led_init(void){ int i; //申請(qǐng)?jiān)O(shè)備號(hào) alloc_chrdev_region(&dev, 0, 1, "tarena"); //初始化字符設(shè)備對(duì)象 cdev_init(&led_cdev, &led_fops); //注冊(cè)字符設(shè)備對(duì)象到內(nèi)核 cdev_add(&led_cdev, dev, 1); //申請(qǐng)GPIO資源和配置GPIO為輸出口，輸出0(省電) for (i = 0; i < ARRAY_SIZE(led_info); i++) { gpio_request(led_info[i].gpio, led_info[i].name); gpio_direction_output(led_info[i].gpio, 0); } return 0;}static void led_exit(void){ int i; //輸出0，釋放GPIO資源 for (i = 0; i < ARRAY_SIZE(led_info); i++) { gpio_set_value(led_info[i].gpio, 0); gpio_free(led_info[i].gpio); } //卸載字符設(shè)備對(duì)象 cdev_del(&led_cdev); //釋放設(shè)備號(hào) unregister_chrdev_region(dev, 1);}module_init(led_init);module_exit(led_exit);MODULE_LICENSE("GPL");
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#include #include #include #include int main(void){ int fd; int udata; //定義用戶緩沖區(qū) //打開(kāi)設(shè)備 //open->....->調(diào)用led_open fd = open("/dev/myled", O_RDWR); if (fd < 0) { printf("打開(kāi)設(shè)備失敗! "); return -1; } //write->...->調(diào)用led_write while (1) { udata = 1; //開(kāi) write(fd, &udata, sizeof(udata)); sleep(1); udata = 0; //關(guān) write(fd, &udata, sizeof(udata)); sleep(1); } //關(guān)閉設(shè)備 //close->...->調(diào)用led_close close(fd); return 0;}
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案例：用戶能夠指定其中某個(gè)燈的開(kāi)關(guān)狀態(tài)；
提示：
用戶不僅僅要告訴燈的開(kāi)關(guān)狀態(tài)，還要告訴驅(qū)動(dòng)用戶現(xiàn)在要想操作哪個(gè)燈；
#include #include #include //struct file_operations#include //struct cdev + 設(shè)備號(hào)#include #include #include //copy_to_user//聲明LED操作的數(shù)據(jù)結(jié)構(gòu)struct led_cmd { int index; int cmd;};//聲明描述LED硬件相關(guān)的數(shù)據(jù)結(jié)構(gòu)struct led_resource { char *name; int gpio;};//定義初始化LED硬件信息static struct led_resource led_info[] = { [0] = { .name = "LED1", .gpio = S5PV210_GPC0(3) }, [1] = { .name = "LED2", .gpio = S5PV210_GPC0(4) }};//定義設(shè)備號(hào)static dev_t dev;//定義字符設(shè)備對(duì)象static struct cdev led_cdev;//調(diào)用關(guān)系：應(yīng)用程序open->....->led_openstatic int led_open(struct inode *inode, struct file *file){ int i; for(i = 0; i < ARRAY_SIZE(led_info); i++) gpio_set_value(led_info[i].gpio, 1); printk("%s ", __func__); return 0; //執(zhí)行成功返回0，執(zhí)行失敗返回負(fù)值 }//調(diào)用關(guān)系：應(yīng)用程序close->...->led_closestatic int led_close(struct inode *inode, struct file *file){ int i; for(i = 0; i < ARRAY_SIZE(led_info); i++) gpio_set_value(led_info[i].gpio, 0); printk("%s ", __func__); return 0; //執(zhí)行成功返回0，執(zhí)行失敗返回負(fù)值 }//調(diào)用關(guān)系：應(yīng)用程序read->...->led_readstatic ssize_t led_read(struct file *file, char __user *buf, size_t count, loff_t *ppos){ //定義初始化內(nèi)核緩沖區(qū)(存儲(chǔ)空間再后1G虛擬內(nèi)存中) int kdata = 0x5555; //將內(nèi)核數(shù)據(jù)上報(bào)給用戶 //切記：buf雖然保存的用戶緩沖區(qū)的首地址，但不能直接訪問(wèn) //*(int *)buf = kdata;錯(cuò)誤 copy_to_user(buf, &kdata, sizeof(kdata)); printk("%s ", __func__); return sizeof(kdata); //失敗返回負(fù)值，成功返回實(shí)際讀取的字節(jié)數(shù)}//調(diào)用關(guān)系：應(yīng)用程序write->...->最終調(diào)用led_writestatic ssize_t led_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos){ //定義內(nèi)核緩沖區(qū) struct led_cmd kdata; //拷貝用戶數(shù)據(jù)到內(nèi)核 copy_from_user(&kdata, buf, sizeof(kdata)); //開(kāi)或者關(guān)燈 gpio_set_value(led_info[kdata.index - 1].gpio, kdata.cmd); printk("%s:第%d燈被%s ", __func__, kdata.index, kdata.cmd?"打開(kāi)":"關(guān)閉"); return count; //失敗返回負(fù)值，成功返回寫(xiě)入的字節(jié)數(shù)}//定義初始化硬件操作方法static struct file_operations led_fops = { .owner = THIS_MODULE, .open = led_open, //打開(kāi)設(shè)備 .release = led_close, //關(guān)閉設(shè)備 .read = led_read, //讀取設(shè)備 .write = led_write //寫(xiě)設(shè)備};static int led_init(void){ int i; //申請(qǐng)?jiān)O(shè)備號(hào) alloc_chrdev_region(&dev, 0, 1, "tarena"); //初始化字符設(shè)備對(duì)象 cdev_init(&led_cdev, &led_fops); //注冊(cè)字符設(shè)備對(duì)象到內(nèi)核 cdev_add(&led_cdev, dev, 1); //申請(qǐng)GPIO資源和配置GPIO為輸出口，輸出0(省電) for (i = 0; i < ARRAY_SIZE(led_info); i++) { gpio_request(led_info[i].gpio, led_info[i].name); gpio_direction_output(led_info[i].gpio, 0); } return 0;}static void led_exit(void){ int i; //輸出0，釋放GPIO資源 for (i = 0; i < ARRAY_SIZE(led_info); i++) { gpio_set_value(led_info[i].gpio, 0); gpio_free(led_info[i].gpio); } //卸載字符設(shè)備對(duì)象 cdev_del(&led_cdev); //釋放設(shè)備號(hào) unregister_chrdev_region(dev, 1);}module_init(led_init);module_exit(led_exit);MODULE_LICENSE("GPL");
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#include #include #include #include //聲明LED操作的數(shù)據(jù)結(jié)構(gòu)struct led_cmd { int index; //指定燈的編號(hào) int cmd; //開(kāi)關(guān)命令};int main(void){ int fd; struct led_cmd udata; //定義用戶緩沖區(qū) //打開(kāi)設(shè)備 //open->....->調(diào)用led_open fd = open("/dev/myled", O_RDWR); if (fd < 0) { printf("打開(kāi)設(shè)備失敗!
"); return -1; } //write->...->調(diào)用led_write while (1) { udata.index = 1; //第一個(gè)燈 udata.cmd = 1; //開(kāi) write(fd, &udata, sizeof(udata)); sleep(1); udata.index = 2; //第二個(gè)燈 write(fd, &udata, sizeof(udata)); sleep(1); } //關(guān)閉設(shè)備 //close->...->調(diào)用led_close close(fd); return 0;}
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