Resources

I. usb Foundation

The usb of stm32 is also the interface that many companies are using. The usb can reach 12M/s at full speed. As a virtual serial interface, it's still good. The whole protocol of usb is very complex. I have sorted out the usb usage in the next few years, explained the usb software architecture, and some important knowledge points.

2. demo Engineering of cubemx Generating usb Virtual Serial Port

usb_vcp_demo warehouse link

Download Warehouse:

git clone https://github.com/yangang123/usb_vcp_demo.git

Step 2.1:

1. The selection board is stm32f4 discovery
2. Selection of external crystal oscillator
3. Setting the system clock is 168MHz
4. Setting USB as device
5. The class that sets up the slave device of USB is vcp
6. Setting the stack is 0x600 [Note]
7. Set Reset
8. View Port
9. View the results

2.2 Testing:

PC : WIN10
Software: Friendly Arm Serial Port Assistant
Keil: MDK5
Veneer: stm32f4 discory

2.3 Testing process:

1. KEIL to set up after downloading, automatic reset
2. Check which COM port is on the computer
3. The program sends one character'a'per second.
4. The serial assistant sends 1 character'a'per second

The entire project has been submitted to github

Address:

How to deal with sending and receiving

Both the receiving and sending interfaces are in usbd_cdc_if.c.

3.1 Data buffer size configuration is as follows

#define APP_RX_DATA_SIZE  4
#define APP_TX_DATA_SIZE  4

3.2 Send Data

To send data, use the following api
uint8_t CDC_Transmit_FS(uint8_t* Buf, uint16_t Len)
Here is the 1s cycle for sending "a" data

HAL_Delay(1000);
char *string = "a";
CDC_Transmit_FS((uint8_t*)string, 1);

3.3 Receiving Data

The receiving buffer uses uint8_t UserRxBufferFS[APP_RX_DATA_SIZE];
The length of received data int recv_len = 0;
The interface for receiving data is static int8_t CDC_Receive_FS (uint8_t*Buf, uint32_t*Len), which receives data.

static int8_t CDC_Receive_FS (uint8_t* Buf, uint32_t *Len)
{ 
  recv_len = *Len;
  USBD_CDC_SetRxBuffer(&hUsbDeviceFS, &Buf[0]);
  USBD_CDC_ReceivePacket(&hUsbDeviceFS);
  return (USBD_OK);
}

IV. Principles of Sending and Receiving

arrangement	function	Main documents
APP	application layer	usbd_cdc_if.c
calss	Different devices, different data	usb_cdc.c
core	Processing of USB Data Buffer	usb_core.c
HAL	Hardware interrupt processing	stm32f4_ll_usb.c

4.1 Send Data

USB_EPStartXfer: Start an Endpoint Transfer
USBx_INEP: Enabling EP
USB_WritePacket: Data Writing to fifo

CDC_Transmit_FS((uint8_t*)string, 15); 
    -> USBD_CDC_TransmitPacket(&hUsbDeviceFS);
        ->   USBD_LL_Transmit(pdev,  CDC_IN_EP, hcdc->TxBuffer,hcdc->TxLength);
            ->   hal_status = HAL_PCD_EP_Transmit(pdev->pData, ep_addr, pbuf, size);
                -> HAL_StatusTypeDef USB_EPStartXfer(USB_OTG_GlobalTypeDef *USBx , USB_OTG_EPTypeDef *ep, uint8_t dma)
                    ->USBx_INEP(ep->num)->DIEPCTL |= (USB_OTG_DIEPCTL_CNAK | USB_OTG_DIEPCTL_EPENA);
                    ->USB_WritePacket(USBx, ep->xfer_buff, ep->num, ep->xfer_len, dma);

4.2 Receiving Data

HAL_PCD_IRQHandler(&hpcd_USB_OTG_FS);
    -> HAL_PCD_DataOutStageCallback(hpcd, epnum);
        -> USBD_LL_DataOutStage((USBD_HandleTypeDef*)hpcd->pData, epnum, hpcd->OUT_ep[epnum].xfer_buff);
            -> pdev->pClass->DataOut(pdev, epnum); 
                ->  ((USBD_CDC_ItfTypeDef *)pdev->pUserData)->Receive(hcdc->RxBuffer, &hcdc->RxLength);

4.2.1 Interface DataOut

Interface Architecture

  typedef struct _Dev   ice_cb{
  uint8_t  (*DataOut)(struct _USBD_HandleTypeDef *pdev , uint8_t epnum); 

Register the DataOut interface

USBD_ClassTypeDef  USBD_CDC = {
  USBD_CDC_DataOut,

4.2.2 Interface Receive

Interface Architecture

typedef struct _USBD_CDC_Itf
{
  int8_t (* Init)          (void);
  int8_t (* DeInit)        (void);
  int8_t (* Control)       (uint8_t, uint8_t * , uint16_t);   
  int8_t (* Receive)       (uint8_t *, uint32_t *);  
}USBD_CDC_ItfTypeDef;

Registration (* Receive) This interface function

USBD_CDC_ItfTypeDef USBD_Interface_fops_FS = 
{
  CDC_Init_FS,
  CDC_DeInit_FS,
  CDC_Control_FS,  
  CDC_Receive_FS
};