每个芯片厂商都会提供一套属于自己的外设驱动及应用程序，这也是我们所说的生态的一部分，可以在官网下载。我们这里主要讲解STM32F103的USB驱动，所以我们需要去ST的官网下载我们需要的驱动程序，STM32F10x, STM32L1xx and STM32F3xx USB full speed device library (UM0424)。

2 STM32-USB-FS设备固件库

2.1 USB应用程序层次结构

下图显示了典型USB的不同组件之间的交互应用程序和USB FS设备库。

从上图可知，USB设备固件库被分为两层：

STM32_USB-FS_Device_Driver：该层管理与USB-FS_ Device外围设备和USB标准协议的直接通信。STM32_USBFS_ Device_Driver符合USB 2.0规范，与标准STM32标准外设库分离。
Application Interface layer：该层为用户提供了库核心和最终应用程序之间的完整接口。

下图显示了USB FS设备库的程序包组织以及所有演示和子文件夹。

2.2 USB-FS_Device peripheral interface

USB全速设备外设接口层主要由以下部分组成：

硬件抽象层
正确传输中断服务例程
数据传输管理

2.3 USB-FS-Device_Driver medium layer

USB全速设备驱动中间层主要由以下部分组成：

USB设备全局变量初始化
USB协议管理
简化了对端点的读写访问功能（USB-FS_Device外围设备的抽象层）
库中使用的USB定义和类型
根据使用的评估板定义硬件

2.3 Application interface

应用接口主要由以下部分组成：

USB全速设备配置文件
USB设备描述符
USB设备应用程序特定属性
不带控制端点的正确传输中断例程
USB设备中断处理函数
USB设备电源和连接管理函数

3 代码讲解

代码讲解主要涉及以下几个方面：

初始化
描述符
中断处理函数
- 复位函数
- 正确传输完成函数

这里以“VirtualComport_Loopback”工程为例进行讲解。

3.1 初始化代码讲解

GPIO初始化

GPIO初始化程序主要是初始化通信所使用的DM和DP引脚以及USB全速设备的DP上拉引脚。


void Set_System(void)
{
  GPIO_InitTypeDef  GPIO_InitStructure;  
 
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
  
  /********************************************/
  /*  Configure USB DM/DP pins                */
  /********************************************/
  
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_11 | GPIO_Pin_12;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
  GPIO_Init(GPIOA, &GPIO_InitStructure);
  
  /* USB_DISCONNECT used as USB pull-up */
  GPIO_InitStructure.GPIO_Pin = USB_DISCONNECT_PIN;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_OD;
  GPIO_Init(USB_DISCONNECT, &GPIO_InitStructure);
  
  /* Enable the USB disconnect GPIO clock */
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIO_DISCONNECT, ENABLE);
}

USB时钟配置

USB时钟配置主要是配置USB的PHY时钟，运行在48MHz的时钟下（系统时钟72M），并使能USB时钟。


void Set_USBClock(void)
{
  /* Select USBCLK source */
  RCC_USBCLKConfig(RCC_USBCLKSource_PLLCLK_1Div5);
  
  /* Enable the USB clock */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_USB, ENABLE);
}

USB中断初始化

USB中断初始化，主要是使能USB的中断，并且使能中断屏蔽位。


void USB_Interrupts_Config(void)
{
    NVIC_InitTypeDef NVIC_InitStructure;
 
    /* 2 bit for pre-emption priority, 2 bits for subpriority */
    NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);
 
 
    /* Enable the USB interrupt */
    NVIC_InitStructure.NVIC_IRQChannel = USB_LP_CAN1_RX0_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);
 
    /* Enable the USB Wake-up interrupt */
    NVIC_InitStructure.NVIC_IRQChannel = USBWakeUp_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
    NVIC_Init(&NVIC_InitStructure);   
 
}


RESULT PowerOn(void)
{
  uint16_t wRegVal;
  
#if !defined (USE_NUCLEO)
  /*** cable plugged-in ? ***/
  USB_Cable_Config(ENABLE);
#endif
 
  /*** CNTR_PWDN = 0 ***/
  wRegVal = CNTR_FRES;
  _SetCNTR(wRegVal);
 
  /* The following sequence is recommended:
    1- FRES = 0
    2- Wait until RESET flag = 1 (polling)
    3- clear ISTR register */
 
  /*** CNTR_FRES = 0 ***/
  wInterrupt_Mask = 0;
  
  _SetCNTR(wInterrupt_Mask);
  
  /* Wait until RESET flag = 1 (polling) */
  while((_GetISTR()&ISTR_RESET) == 1);
  
  /*** Clear pending interrupts ***/
  SetISTR(0);
  
  /*** Set interrupt mask ***/
  wInterrupt_Mask = CNTR_RESETM | CNTR_SUSPM | CNTR_WKUPM;
  _SetCNTR(wInterrupt_Mask);
  
  return USB_SUCCESS;
}
 
uint32_t USB_SIL_Init(void)
{
  /* USB interrupts initialization */
  /* clear pending interrupts */
  _SetISTR(0);
  wInterrupt_Mask = IMR_MSK;
  /* set interrupts mask */
  _SetCNTR(wInterrupt_Mask);
  return 0;
}
 
void Virtual_Com_Port_init(void)
{
 
  /* Update the serial number string descriptor with the data from the unique
  ID*/
  Get_SerialNum();
 
  pInformation->Current_Configuration = 0;
 
  /* Connect the device */
  PowerOn();
 
  /* Perform basic device initialization operations */
  USB_SIL_Init();
 
  bDeviceState = UNCONNECTED;
}

经过上面的配置，当USB设备端接入主机的时候，设备端的中断处理函数就能响应相应的中断请求，开始建立通信。

3.2 描述符讲解

描述符放在“usb_desc.c”和“usb_desc.h”文件中，更多细节参见USB -- 初识USB协议（一）。

设备描述符

包含了设备的基本信息，比如USB版本号，端点0的传输大小，VID，PID，设备的类型等。


const uint8_t Virtual_Com_Port_DeviceDescriptor[] =
{
    0x12,   /* bLength */
    USB_DEVICE_DESCRIPTOR_TYPE,     /* bDescriptorType */
    0x00,
    0x02,   /* bcdUSB = 2.00 */
    0x02,   /* bDeviceClass: CDC */
    0x02,   /* bDeviceSubClass */
    0x02,   /* bDeviceProtocol */
    0x40,   /* bMaxPacketSize0 */
    0x83,
    0x04,   /* idVendor = 0x0483 */
    0x40,
    0x57,   /* idProduct = 0x7540 */
    0x00,
    0x02,   /* bcdDevice = 2.00 */
    1,              /* Index of string descriptor describing manufacturer */
    2,              /* Index of string descriptor describing product */
    3,              /* Index of string descriptor describing the device's serial number */
    0x01    /* bNumConfigurations */
};

配置描述符

配置描述符数组包含了配置描述符、接口描述符、功能描述符，端点描述符等，具体的描述符含义根据每种USB的CLASS不同而含义有所不同，后期小节会陆续讲解。


const uint8_t Virtual_Com_Port_ConfigDescriptor[] =
{
    /*Configuration Descriptor*/
    0x09,   /* bLength: Configuration Descriptor size */
    USB_CONFIGURATION_DESCRIPTOR_TYPE,      /* bDescriptorType: Configuration */
    VIRTUAL_COM_PORT_SIZ_CONFIG_DESC,       /* wTotalLength:no of returned bytes */
    0x00,
    0x02,   /* bNumInterfaces: 2 interface */
    0x01,   /* bConfigurationValue: Configuration value */
    0x00,   /* iConfiguration: Index of string descriptor describing the configuration */
    0xC0,   /* bmAttributes: self powered */
    0x32,   /* MaxPower 0 mA */
    /*Interface Descriptor*/
    0x09,   /* bLength: Interface Descriptor size */
    USB_INTERFACE_DESCRIPTOR_TYPE,  /* bDescriptorType: Interface */
    /* Interface descriptor type */
    0x00,   /* bInterfaceNumber: Number of Interface */
    0x00,   /* bAlternateSetting: Alternate setting */
    0x01,   /* bNumEndpoints: One endpoints used */
    0x02,   /* bInterfaceClass: Communication Interface Class */
    0x02,   /* bInterfaceSubClass: Abstract Control Model */
    0x01,   /* bInterfaceProtocol: Common AT commands */
    0x00,   /* iInterface: */
    /*Header Functional Descriptor*/
    0x05,   /* bLength: Endpoint Descriptor size */
    0x24,   /* bDescriptorType: CS_INTERFACE */
    0x00,   /* bDescriptorSubtype: Header Func Desc */
    0x10,   /* bcdCDC: spec release number */
    0x01,
    /*Call Management Functional Descriptor*/
    0x05,   /* bFunctionLength */
    0x24,   /* bDescriptorType: CS_INTERFACE */
    0x01,   /* bDescriptorSubtype: Call Management Func Desc */
    0x00,   /* bmCapabilities: D0+D1 */
    0x01,   /* bDataInterface: 1 */
    /*ACM Functional Descriptor*/
    0x04,   /* bFunctionLength */
    0x24,   /* bDescriptorType: CS_INTERFACE */
    0x02,   /* bDescriptorSubtype: Abstract Control Management desc */
    0x02,   /* bmCapabilities */
    /*Union Functional Descriptor*/
    0x05,   /* bFunctionLength */
    0x24,   /* bDescriptorType: CS_INTERFACE */
    0x06,   /* bDescriptorSubtype: Union func desc */
    0x00,   /* bMasterInterface: Communication class interface */
    0x01,   /* bSlaveInterface0: Data Class Interface */
    /*Endpoint 2 Descriptor*/
    0x07,   /* bLength: Endpoint Descriptor size */
    USB_ENDPOINT_DESCRIPTOR_TYPE,   /* bDescriptorType: Endpoint */
    0x82,   /* bEndpointAddress: (IN2) */
    0x03,   /* bmAttributes: Interrupt */
    VIRTUAL_COM_PORT_INT_SIZE,      /* wMaxPacketSize: */
    0x00,
    0xFF,   /* bInterval: */
    /*Data class interface descriptor*/
    0x09,   /* bLength: Endpoint Descriptor size */
    USB_INTERFACE_DESCRIPTOR_TYPE,  /* bDescriptorType: */
    0x01,   /* bInterfaceNumber: Number of Interface */
    0x00,   /* bAlternateSetting: Alternate setting */
    0x02,   /* bNumEndpoints: Two endpoints used */
    0x0A,   /* bInterfaceClass: CDC */
    0x00,   /* bInterfaceSubClass: */
    0x00,   /* bInterfaceProtocol: */
    0x00,   /* iInterface: */
    /*Endpoint 3 Descriptor*/
    0x07,   /* bLength: Endpoint Descriptor size */
    USB_ENDPOINT_DESCRIPTOR_TYPE,   /* bDescriptorType: Endpoint */
    0x03,   /* bEndpointAddress: (OUT3) */
    0x02,   /* bmAttributes: Bulk */
    VIRTUAL_COM_PORT_DATA_SIZE,             /* wMaxPacketSize: */
    0x00,
    0x00,   /* bInterval: ignore for Bulk transfer */
    /*Endpoint 1 Descriptor*/
    0x07,   /* bLength: Endpoint Descriptor size */
    USB_ENDPOINT_DESCRIPTOR_TYPE,   /* bDescriptorType: Endpoint */
    0x81,   /* bEndpointAddress: (IN1) */
    0x02,   /* bmAttributes: Bulk */
    VIRTUAL_COM_PORT_DATA_SIZE,             /* wMaxPacketSize: */
    0x00,
    0x00    /* bInterval */
};

其它描述符

其它描述符包括语言描述符，PID描述符、VID描述符，报告描述符等，这些描述符根据不同的厂商，不同的产品以及不同的USB应用而有所不通，我们会在后续的类容对这些描述符做一个简单的讲解。

3.3 中断处理函数

USB驱动最关键的部分在于中断处理函数部分，协议的大部分实现都是在中断中实现的，我们这里简单的讲解一下。首先进入USB中断处理函数，进入到USB_Istr()函数中去。

可以看到USB_Istr()函数实现了USB的中断的所有功能，我们这里只针对几个比较重要的函数进行讲解：

复位函数
正确传输完成函数


void USB_Istr(void)
{
    uint32_t i = 0;
    __IO uint32_t EP[8];
 
    wIstr = _GetISTR();
 
#if (IMR_MSK & ISTR_SOF)
 
    if (wIstr & ISTR_SOF & wInterrupt_Mask)
    {
        _SetISTR((uint16_t)CLR_SOF);
        bIntPackSOF++;
 
#ifdef SOF_CALLBACK
        SOF_Callback();
#endif
    }
 
#endif
    /*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*/
 
#if (IMR_MSK & ISTR_CTR)
 
    if (wIstr & ISTR_CTR & wInterrupt_Mask)
    {
        /* servicing of the endpoint correct transfer interrupt */
        /* clear of the CTR flag into the sub */
        CTR_LP();
#ifdef CTR_CALLBACK
        CTR_Callback();
#endif
    }
 
#endif
    /*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*/
#if (IMR_MSK & ISTR_RESET)
 
    if (wIstr & ISTR_RESET & wInterrupt_Mask)
    {
        _SetISTR((uint16_t)CLR_RESET);
        Device_Property.Reset();
#ifdef RESET_CALLBACK
        RESET_Callback();
#endif
    }
 
#endif
    /*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*/
#if (IMR_MSK & ISTR_DOVR)
 
    if (wIstr & ISTR_DOVR & wInterrupt_Mask)
    {
        _SetISTR((uint16_t)CLR_DOVR);
#ifdef DOVR_CALLBACK
        DOVR_Callback();
#endif
    }
 
#endif
    /*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*/
#if (IMR_MSK & ISTR_ERR)
 
    if (wIstr & ISTR_ERR & wInterrupt_Mask)
    {
        _SetISTR((uint16_t)CLR_ERR);
#ifdef ERR_CALLBACK
        ERR_Callback();
#endif
    }
 
#endif
    /*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*/
#if (IMR_MSK & ISTR_WKUP)
 
    if (wIstr & ISTR_WKUP & wInterrupt_Mask)
    {
        _SetISTR((uint16_t)CLR_WKUP);
        Resume(RESUME_EXTERNAL);
#ifdef WKUP_CALLBACK
        WKUP_Callback();
#endif
    }
 
#endif
    /*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*/
#if (IMR_MSK & ISTR_SUSP)
 
    if (wIstr & ISTR_SUSP & wInterrupt_Mask)
    {
 
        /* check if SUSPEND is possible */
        if (fSuspendEnabled)
        {
            Suspend();
        }
        else
        {
            /* if not possible then resume after xx ms */
            Resume(RESUME_LATER);
        }
 
        /* clear of the ISTR bit must be done after setting of CNTR_FSUSP */
        _SetISTR((uint16_t)CLR_SUSP);
#ifdef SUSP_CALLBACK
        SUSP_Callback();
#endif
    }
 
#endif
    /*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*/
 
#if (IMR_MSK & ISTR_ESOF)
 
    if (wIstr & ISTR_ESOF & wInterrupt_Mask)
    {
        /* clear ESOF flag in ISTR */
        _SetISTR((uint16_t)CLR_ESOF);
 
        if ((_GetFNR()&FNR_RXDP) != 0)
        {
            /* increment ESOF counter */
            esof_counter ++;
 
            /* test if we enter in ESOF more than 3 times with FSUSP =0 and RXDP =1=>> possible missing SUSP flag*/
            if ((esof_counter > 3) && ((_GetCNTR()&CNTR_FSUSP) == 0))
            {
                /* this a sequence to apply a force RESET*/
 
                /*Store CNTR value */
                wCNTR = _GetCNTR();
 
                /*Store endpoints registers status */
                for (i = 0; i < 8; i++) EP[i] = _GetENDPOINT(i);
 
                /*apply FRES */
                wCNTR |= CNTR_FRES;
                _SetCNTR(wCNTR);
 
                /*clear FRES*/
                wCNTR &= ~CNTR_FRES;
                _SetCNTR(wCNTR);
 
                /*poll for RESET flag in ISTR*/
                while ((_GetISTR()&ISTR_RESET) == 0);
 
                /* clear RESET flag in ISTR */
                _SetISTR((uint16_t)CLR_RESET);
 
                /*restore Enpoints*/
                for (i = 0; i < 8; i++)
                    _SetENDPOINT(i, EP[i]);
 
                esof_counter = 0;
            }
        }
        else
        {
            esof_counter = 0;
        }
 
        /* resume handling timing is made with ESOFs */
        Resume(RESUME_ESOF); /* request without change of the machine state */
 
#ifdef ESOF_CALLBACK
        ESOF_Callback();
#endif
    }
 
#endif
} /* USB_Istr */

3.3.1 复位函数

复位是在USB识别到设备的时候，主机主动发出的特定序列，当USB设备收到这个特定序列的时候，就会产生中断相应，并进入中断中去处理相应的函数，这里的复位中断处理函数主要是配置端点的属性及端点的大小。

注意一下宏定义“BTABLE_ADDRESS”的对应的USB中断缓存区地址的偏移，也就是512Byte的RAM空间，宏“ENDP0_RXADDR”等是定义端点的发送和接收地址存放在RAM空间的具体位置，以“BTABLE_ADDRESS”为偏移。


/* buffer table base address */
/* buffer table base address */
#define BTABLE_ADDRESS      (0x00)
 
/* EP0  */
/* rx/tx buffer base address */
#define ENDP0_RXADDR        (0x40)
#define ENDP0_TXADDR        (0x80)
 
/* EP1  */
/* tx buffer base address */
#define ENDP1_TXADDR        (0xC0)
#define ENDP2_TXADDR        (0x100)
#define ENDP3_RXADDR        (0x110)
 
void Virtual_Com_Port_Reset(void)
{
  /* Set Virtual_Com_Port DEVICE as not configured */
  pInformation->Current_Configuration = 0;
 
  /* Current Feature initialization */
  pInformation->Current_Feature = Virtual_Com_Port_ConfigDescriptor[7];
 
  /* Set Virtual_Com_Port DEVICE with the default Interface*/
  pInformation->Current_Interface = 0;
 
  SetBTABLE(BTABLE_ADDRESS);
 
  /* Initialize Endpoint 0 */
  SetEPType(ENDP0, EP_CONTROL);
  SetEPTxStatus(ENDP0, EP_TX_STALL);
  SetEPRxAddr(ENDP0, ENDP0_RXADDR);
  SetEPTxAddr(ENDP0, ENDP0_TXADDR);
  Clear_Status_Out(ENDP0);
  SetEPRxCount(ENDP0, Device_Property.MaxPacketSize);
  SetEPRxValid(ENDP0);
 
  /* Initialize Endpoint 1 */
  SetEPType(ENDP1, EP_BULK);
  SetEPTxAddr(ENDP1, ENDP1_TXADDR);
  SetEPTxStatus(ENDP1, EP_TX_NAK);
  SetEPRxStatus(ENDP1, EP_RX_DIS);
 
  /* Initialize Endpoint 2 */
  SetEPType(ENDP2, EP_INTERRUPT);
  SetEPTxAddr(ENDP2, ENDP2_TXADDR);
  SetEPRxStatus(ENDP2, EP_RX_DIS);
  SetEPTxStatus(ENDP2, EP_TX_NAK);
 
  /* Initialize Endpoint 3 */
  SetEPType(ENDP3, EP_BULK);
  SetEPRxAddr(ENDP3, ENDP3_RXADDR);
  SetEPRxCount(ENDP3, VIRTUAL_COM_PORT_DATA_SIZE);
  SetEPRxStatus(ENDP3, EP_RX_VALID);
  SetEPTxStatus(ENDP3, EP_TX_DIS);
 
  /* Set this device to response on default address */
  SetDeviceAddress(0);
  
  bDeviceState = ATTACHED;
}

3.3.2 正确传输完成函数

正确传输完成函数分为枚举过程（端点0）的正确传输完成函数和非端点0的正确传输完成函数。


void CTR_LP(void)
{
    __IO uint16_t wEPVal = 0;
 
    /* stay in loop while pending interrupts */
    while (((wIstr = _GetISTR()) & ISTR_CTR) != 0)
    {
        /* extract highest priority endpoint number */
        EPindex = (uint8_t)(wIstr & ISTR_EP_ID);
 
        if (EPindex == 0)
        {
            /* Decode and service control endpoint interrupt */
            /* calling related service routine */
            /* (Setup0_Process, In0_Process, Out0_Process) */
 
            /* save RX & TX status */
            /* and set both to NAK */
 
            SaveRState = _GetENDPOINT(ENDP0);
            SaveTState = SaveRState & EPTX_STAT;
            SaveRState &=  EPRX_STAT;
 
            _SetEPRxTxStatus(ENDP0, EP_RX_NAK, EP_TX_NAK);
 
            /* DIR bit = origin of the interrupt */
 
            if ((wIstr & ISTR_DIR) == 0)
            {
                /* DIR = 0 */
 
                /* DIR = 0      => IN  int */
                /* DIR = 0 implies that (EP_CTR_TX = 1) always  */
 
                _ClearEP_CTR_TX(ENDP0);
                In0_Process();
 
                /* before terminate set Tx & Rx status */
 
                _SetEPRxTxStatus(ENDP0, SaveRState, SaveTState);
                return;
            }
            else
            {
                /* DIR = 1 */
 
                /* DIR = 1 & CTR_RX       => SETUP or OUT int */
                /* DIR = 1 & (CTR_TX | CTR_RX) => 2 int pending */
 
                wEPVal = _GetENDPOINT(ENDP0);
 
                if ((wEPVal & EP_SETUP) != 0)
                {
                    _ClearEP_CTR_RX(ENDP0); /* SETUP bit kept frozen while CTR_RX = 1 */
                    Setup0_Process();
                    /* before terminate set Tx & Rx status */
 
                    _SetEPRxTxStatus(ENDP0, SaveRState, SaveTState);
                    return;
                }
 
                else if ((wEPVal & EP_CTR_RX) != 0)
                {
                    _ClearEP_CTR_RX(ENDP0);
                    Out0_Process();
                    /* before terminate set Tx & Rx status */
 
                    _SetEPRxTxStatus(ENDP0, SaveRState, SaveTState);
                    return;
                }
            }
        }/* if(EPindex == 0) */
        else
        {
            /* Decode and service non control endpoints interrupt  */
 
            /* process related endpoint register */
            wEPVal = _GetENDPOINT(EPindex);
 
            if ((wEPVal & EP_CTR_RX) != 0)
            {
                /* clear int flag */
                _ClearEP_CTR_RX(EPindex);
 
                /* call OUT service function */
                (*pEpInt_OUT[EPindex - 1])();
 
            } /* if((wEPVal & EP_CTR_RX) */
 
            if ((wEPVal & EP_CTR_TX) != 0)
            {
                /* clear int flag */
                _ClearEP_CTR_TX(EPindex);
 
                /* call IN service function */
                (*pEpInt_IN[EPindex - 1])();
            } /* if((wEPVal & EP_CTR_TX) != 0) */
 
        }/* if(EPindex == 0) else */
 
    }/* while(...) */
}

3.3.2.1 枚举过程正确传输完成函数

枚举过程的正确传输完成函数主要是接收SETUP指令请求，并相应的告知USB主机设备的描述符信息。

以下代码是处理USB主机的数据，把USB主机的SETUP请求数据存在pInformation结构体中，并在后续的函数进行指令的解析，并通过相对应的SETUP请求发送相对应的数据。


uint8_t Setup0_Process(void)
{
 
    union
    {
        uint8_t* b;
        uint16_t* w;
    } pBuf;
#if defined STM32F303xE || defined STM32F302x8
    uint16_t offset = 0;
    pBuf.b = (uint8_t *)( PMAAddr + _GetEPRxAddr(ENDP0));
#else
    uint16_t offset = 1;
 
    pBuf.b = PMAAddr + (uint8_t *)(_GetEPRxAddr(ENDP0) * 2); /* *2 for 32 bits addr */
#endif
 
    if (pInformation->ControlState != PAUSE)
    {
        pInformation->USBbmRequestType = *pBuf.b++; /* bmRequestType */
        pInformation->USBbRequest = *pBuf.b++; /* bRequest */
        pBuf.w += offset;  /* word not accessed because of 32 bits addressing */
        pInformation->USBwValue = ByteSwap(*pBuf.w++); /* wValue */
        pBuf.w += offset;  /* word not accessed because of 32 bits addressing */
        pInformation->USBwIndex  = ByteSwap(*pBuf.w++); /* wIndex */
        pBuf.w += offset;  /* word not accessed because of 32 bits addressing */
        pInformation->USBwLength = *pBuf.w; /* wLength */
    }
 
    pInformation->ControlState = SETTING_UP;
 
    if (pInformation->USBwLength == 0)
    {
        /* Setup with no data stage */
        NoData_Setup0();
    }
    else
    {
        /* Setup with data stage */
        Data_Setup0();
    }
 
    return Post0_Process();
}


void Data_Setup0(void)
{
    uint8_t *(*CopyRoutine)(uint16_t);
    RESULT Result;
    uint32_t Request_No = pInformation->USBbRequest;
 
    uint32_t Related_Endpoint, Reserved;
    uint32_t wOffset, Status;
 
 
 
    CopyRoutine = NULL;
    wOffset = 0;
 
    /*GET DESCRIPTOR*/
    if (Request_No == GET_DESCRIPTOR)
    {
        if (Type_Recipient == (STANDARD_REQUEST | DEVICE_RECIPIENT))
        {
            uint8_t wValue1 = pInformation->USBwValue1;
 
            if (wValue1 == DEVICE_DESCRIPTOR)
            {
                CopyRoutine = pProperty->GetDeviceDescriptor;
            }
 
#ifdef LPM_ENABLED
            else if (wValue1 == DEVICE_BOS_DESCRIPTOR)
            {
                CopyRoutine = pProperty->GetBosDescriptor;
            }
 
#endif
            else if (wValue1 == CONFIG_DESCRIPTOR)
            {
                CopyRoutine = pProperty->GetConfigDescriptor;
            }
            else if (wValue1 == STRING_DESCRIPTOR)
            {
                CopyRoutine = pProperty->GetStringDescriptor;
            }  /* End of GET_DESCRIPTOR */
        }
    }
 
    /*GET STATUS*/
    else if ((Request_No == GET_STATUS) && (pInformation->USBwValue == 0)
             && (pInformation->USBwLength == 0x0002)
             && (pInformation->USBwIndex1 == 0))
    {
        /* GET STATUS for Device*/
        if ((Type_Recipient == (STANDARD_REQUEST | DEVICE_RECIPIENT))
                && (pInformation->USBwIndex == 0))
        {
            CopyRoutine = Standard_GetStatus;
        }
 
        /* GET STATUS for Interface*/
        else if (Type_Recipient == (STANDARD_REQUEST | INTERFACE_RECIPIENT))
        {
            if (((*pProperty->Class_Get_Interface_Setting)(pInformation->USBwIndex0, 0) == USB_SUCCESS)
                    && (pInformation->Current_Configuration != 0))
            {
                CopyRoutine = Standard_GetStatus;
            }
        }
 
        /* GET STATUS for EndPoint*/
        else if (Type_Recipient == (STANDARD_REQUEST | ENDPOINT_RECIPIENT))
        {
            Related_Endpoint = (pInformation->USBwIndex0 & 0x0f);
            Reserved = pInformation->USBwIndex0 & 0x70;
 
            if (ValBit(pInformation->USBwIndex0, 7))
            {
                /*Get Status of endpoint & stall the request if the related_ENdpoint
                is Disabled*/
                Status = _GetEPTxStatus(Related_Endpoint);
            }
            else
            {
                Status = _GetEPRxStatus(Related_Endpoint);
            }
 
            if ((Related_Endpoint < Device_Table.Total_Endpoint) && (Reserved == 0)
                    && (Status != 0))
            {
                CopyRoutine = Standard_GetStatus;
            }
        }
 
    }
 
    /*GET CONFIGURATION*/
    else if (Request_No == GET_CONFIGURATION)
    {
        if (Type_Recipient == (STANDARD_REQUEST | DEVICE_RECIPIENT))
        {
            CopyRoutine = Standard_GetConfiguration;
        }
    }
    /*GET INTERFACE*/
    else if (Request_No == GET_INTERFACE)
    {
        if ((Type_Recipient == (STANDARD_REQUEST | INTERFACE_RECIPIENT))
                && (pInformation->Current_Configuration != 0) && (pInformation->USBwValue == 0)
                && (pInformation->USBwIndex1 == 0) && (pInformation->USBwLength == 0x0001)
                && ((*pProperty->Class_Get_Interface_Setting)(pInformation->USBwIndex0, 0) == USB_SUCCESS))
        {
            CopyRoutine = Standard_GetInterface;
        }
 
    }
 
    if (CopyRoutine)
    {
        pInformation->Ctrl_Info.Usb_wOffset = wOffset;
        pInformation->Ctrl_Info.CopyData = CopyRoutine;
        /* sb in the original the cast to word was directly */
        /* now the cast is made step by step */
        (*CopyRoutine)(0);
        Result = USB_SUCCESS;
    }
    else
    {
        Result = (*pProperty->Class_Data_Setup)(pInformation->USBbRequest);
 
        if (Result == USB_NOT_READY)
        {
            pInformation->ControlState = PAUSE;
            return;
        }
    }
 
    if (pInformation->Ctrl_Info.Usb_wLength == 0xFFFF)
    {
        /* Data is not ready, wait it */
        pInformation->ControlState = PAUSE;
        return;
    }
 
    if ((Result == USB_UNSUPPORT) || (pInformation->Ctrl_Info.Usb_wLength == 0))
    {
        /* Unsupported request */
        pInformation->ControlState = STALLED;
        return;
    }
 
 
    if (ValBit(pInformation->USBbmRequestType, 7))
    {
        /* Device ==> Host */
        __IO uint32_t wLength = pInformation->USBwLength;
 
        /* Restrict the data length to be the one host asks for */
        if (pInformation->Ctrl_Info.Usb_wLength > wLength)
        {
            pInformation->Ctrl_Info.Usb_wLength = wLength;
        }
 
        else if (pInformation->Ctrl_Info.Usb_wLength < pInformation->USBwLength)
        {
            if (pInformation->Ctrl_Info.Usb_wLength < pProperty->MaxPacketSize)
            {
                Data_Mul_MaxPacketSize = FALSE;
            }
            else if ((pInformation->Ctrl_Info.Usb_wLength % pProperty->MaxPacketSize) == 0)
            {
                Data_Mul_MaxPacketSize = TRUE;
            }
        }
 
        pInformation->Ctrl_Info.PacketSize = pProperty->MaxPacketSize;
        DataStageIn();
    }
    else
    {
        pInformation->ControlState = OUT_DATA;
        vSetEPRxStatus(EP_RX_VALID); /* enable for next data reception */
    }
 
    return;
}

3.3.2.2 非端点0正确传输完成函数

非控制端点0正确传输完成函数根据不同的USB应用存在不同的差距，但是主体框架已经完成，只需要用户在特定的框架中填写特定的程序即可。

比如当前程序只用到端点1的TX和端点3的RX，就只需要在端点1的TX和端点3的RX中编写相应的应用程序，其它端点不必理会。


/* associated to defined endpoints */
/*#define  EP1_IN_Callback   NOP_Process*/
#define  EP2_IN_Callback   NOP_Process
#define  EP3_IN_Callback   NOP_Process
#define  EP4_IN_Callback   NOP_Process
#define  EP5_IN_Callback   NOP_Process
#define  EP6_IN_Callback   NOP_Process
#define  EP7_IN_Callback   NOP_Process
 
#define  EP1_OUT_Callback   NOP_Process
#define  EP2_OUT_Callback   NOP_Process
/*#define  EP3_OUT_Callback   NOP_Process*/
#define  EP4_OUT_Callback   NOP_Process
#define  EP5_OUT_Callback   NOP_Process
#define  EP6_OUT_Callback   NOP_Process
#define  EP7_OUT_Callback   NOP_Process
 
void (*pEpInt_IN[7])(void) =
{
    EP1_IN_Callback,
    EP2_IN_Callback,
    EP3_IN_Callback,
    EP4_IN_Callback,
    EP5_IN_Callback,
    EP6_IN_Callback,
    EP7_IN_Callback,
};
 
void (*pEpInt_OUT[7])(void) =
{
    EP1_OUT_Callback,
    EP2_OUT_Callback,
    EP3_OUT_Callback,
    EP4_OUT_Callback,
    EP5_OUT_Callback,
    EP6_OUT_Callback,
    EP7_OUT_Callback,
};
 
void EP1_IN_Callback (void)
{
    packet_sent = 1;
}
 
void EP3_OUT_Callback(void)
{
    packet_receive = 1;
    Receive_length = GetEPRxCount(ENDP3);
    PMAToUserBufferCopy((unsigned char*)Receive_Buffer, ENDP3_RXADDR, Receive_length);
}

到这里，本章就基本上讲完了，主要还是从应用的角度去简单的讲解了一下代码，如果读者需要更深入的了解代码的结构，还是需要大家仔细去学习USB的驱动源码的。

接下来讲解STM32 USB的虚拟串口环回功能实现，敬请期待。。。

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