FATFS学习之——多任务支持

FATFS学习之——多任务支持

    新版本的FATFS提供对多任务(RTOS)的支持，FATFS作为对设备操作的函数集，而设备在RTOS环境下作为一种临界资源，必然引入同步和互斥的开概念。

    下载最新FATFS V0.10b版本源码, option目录下有一个syscall.c文件，是对RTOS提供的同步和互斥机制的封装。

一、多任务环境支持的配置ffconf.h中，相关定义如下：

#define _FS_REENTRANT1/* 0:Disable or 1:Enable */#define _FS_TIMEOUT1000/* Timeout period in unit of time tick */#define_SYNC_tHANDLE        /* O/S dependent sync object type. e.g. HANDLE, OS_EVENT*, ID, SemaphoreHandle_t and etc.. *//* The _FS_REENTRANT option switches the re-entrancy (thread safe) of the FatFs module.//   0: Disable re-entrancy. _FS_TIMEOUT and _SYNC_t have no effect./   1: Enable re-entrancy. Also user provided synchronization handlers,/      ff_req_grant(), ff_rel_grant(), ff_del_syncobj() and ff_cre_syncobj()/      function must be added to the project.*/

_SYNC_t作为异步操作对像类型，在RAW-OS中定义为mutex，当然也可以定义为信号量，但这样会引入优先级反转问题。

二、syscall.c源文件中对sync object的实现：

    1. 创建一个异步对像

/*------------------------------------------------------------------------*//* Create a Synchronization Object/*------------------------------------------------------------------------*//* This function is called by f_mount() function to create a new/  synchronization object, such as semaphore and mutex. When a 0 is/  returned, the f_mount() function fails with FR_INT_ERR.*/int ff_cre_syncobj (/* 1:Function succeeded, 0:Could not create due to any error */BYTE vol,/* Corresponding logical drive being processed */_SYNC_t* sobj/* Pointer to return the created sync object */){int ret;*sobj = CreateMutex(NULL, FALSE, NULL);/* Win32 */ret = (int)(*sobj != INVALID_HANDLE_VALUE);//*sobj = SyncObjects[vol];//ret = 1;//*sobj = OSMutexCreate(0, &err);//ret = (int)(err == OS_NO_ERR);//      *sobj = xSemaphoreCreateMutex();//ret = (int)(*sobj != NULL);return ret;}

从上面可以看出，对我们熟知的uC/OS-II来讲，异步对像是一个mutex。该函数返回1表示创建成功。

    2. 同理删除一个同步对像如下所示：

/*------------------------------------------------------------------------*//* Delete a Synchronization Object                                        *//*------------------------------------------------------------------------*//* This function is called in f_mount() function to delete a synchronization/  object that created with ff_cre_syncobj() function. When a 0 is/  returned, the f_mount() function fails with FR_INT_ERR.*/int ff_del_syncobj (/* 1:Function succeeded, 0:Could not delete due to any error */_SYNC_t sobj/* Sync object tied to the logical drive to be deleted */){int ret;ret = CloseHandle(sobj);/* Win32 *///ret = 1;/* uITRON (nothing to do) *///OSMutexDel(sobj, OS_DEL_ALWAYS, &err);/* uC/OS-II *///ret = (int)(err == OS_NO_ERR);//      xSemaphoreDelete(sobj);/* FreeRTOS *///ret = 1;return ret;}

    3. 请求同步对像资源可用

/*------------------------------------------------------------------------*//* Request Grant to Access the Volume                                     *//*------------------------------------------------------------------------*//* This function is called on entering file functions to lock the volume./  When a FALSE is returned, the file function fails with FR_TIMEOUT.*/int ff_req_grant (/* TRUE:Got a grant to access the volume, FALSE:Could not get a grant */_SYNC_t sobj/* Sync object to wait */){int ret;ret = (int)(WaitForSingleObject(sobj, _FS_TIMEOUT) == WAIT_OBJECT_0);/* Win32 *///ret = (int)(wai_sem(sobj) == E_OK);/* uITRON *///OSMutexPend(sobj, _FS_TIMEOUT, &err));/* uC/OS-II *///ret = (int)(err == OS_NO_ERR);//ret = (int)(xSemaphoreTake(sobj, _FS_TIMEOUT) == pdTRUE); /* FreeRTOS */return ret;}

    从uC/OS-II来看，就是带超时阻塞在一个mutex上，超时时间为_FS_TIMEOUT，它在配置中定义为1000，即1000个OS_Tick。

    4. 释放同步对像供别的任务所用。

/*------------------------------------------------------------------------*//* Release Grant to Access the Volume                                     *//*------------------------------------------------------------------------*//* This function is called on leaving file functions to unlock the volume.*/void ff_rel_grant (_SYNC_t sobj/* Sync object to be signaled */){ReleaseMutex(sobj);/* Win32 *///sig_sem(sobj);/* uITRON *///OSMutexPost(sobj);/* uC/OS-II *///xSemaphoreGive(sobj);/* FreeRTOS */}

三、 RAW-OS下FATFS多任务支持的代码实现

    1. 配置

#define _FS_REENTRANT1<span style="white-space:pre"></span>/* 0:Disable or 1:Enable */#define _FS_TIMEOUT100             /* Timeout period in unit of time ticks */#define_SYNC_tRAW_MUTEX */* O/S dependent sync object type. e.g. HANDLE, OS_EVENT*, ID and etc.. */

    2. 创建同步对像

int ff_cre_syncobj (/* TRUE:Function succeeded, FALSE:Could not create due to any error */BYTE vol,/* Corresponding logical drive being processed */_SYNC_t *sobj/* Pointer to return the created sync object */){RAW_U16  ret = 0;*sobj = mem_4_malloc(sizeof(RAW_MUTEX));/* 为同步对像申请内存空间 */ret = raw_mutex_create(*sobj, (RAW_U8 *)"fatfs_lock", RAW_MUTEX_INHERIT_POLICY, 0);if (ret == RAW_SUCCESS) {ret = 1;}return ret;}

    3. 删除同步对像   

int ff_del_syncobj (/* TRUE:Function succeeded, FALSE:Could not delete due to any error */_SYNC_t sobj/* Sync object tied to the logical drive to be deleted */){RAW_U16  ret = 0;ret = raw_mutex_delete(sobj);mem_4_free(sobj);if (ret == RAW_SUCCESS) {ret = 1;}return ret;}

    4. 申请资源可用

int ff_req_grant (/* TRUE:Got a grant to access the volume, FALSE:Could not get a grant */_SYNC_t sobj/* Sync object to wait */){RAW_U16  ret = 0;ret = raw_mutex_get(sobj, RAW_WAIT_FOREVER);  /* 阻塞直到资源可用 */ if (ret == RAW_SUCCESS) {ret = 1;}return ret;}

    4. 释放资源

void ff_rel_grant (_SYNC_t sobj/* Sync object to be signaled */){RAW_U16 ret;ret = raw_mutex_put(sobj);if (ret != RAW_SUCCESS) {RAW_ASSERT(0);}}