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/**
@page CDC_Standalone USB Device Communication (CDC) application
@verbatim
******************************************************************************
* @file USB_Device/CDC_Standalone/readme.txt
* @author MCD Application Team
* @brief Description of the USB Device CDC application.
******************************************************************************
* @attention
*
* Copyright (c) 2016 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
@endverbatim
@par Application Description
Use of the USB device application based on the Device Communication Class (CDC) and
following the PSTN subprotocol. This application uses the USB Device and UART peripherals.
This is a typical application on how to use the STM32F7xx USB OTG Device peripheral where the STM32 MCU
behaves as a USB-to-RS232 bridge following the Virtual COM Port (VCP) implementation.
- On one side, the STM32 exchanges data with a PC host through USB interface in Device mode.
- On the other side, the STM32 exchanges data with other devices (same host, other host,
other devices…) through the UART interface (RS232).
At the beginning of the main program the HAL_Init() function is called to reset all the peripherals,
initialize the Flash interface and the systick. The user is provided with the SystemClock_Config()
function to configure the system clock (SYSCLK) to run at 216 MHz. The Full Speed (FS) USB module uses
internally a 48-MHz clock which is coming from a specific output of two PLLs: main PLL or PLL SAI.
In the High Speed (HS) mode the USB clock (60 MHz) is driven by the ULPI.
The 48 MHz clock for the USB FS can be derived from one of the two following sources:
– PLL clock (clocked by the HSE): If the USB uses the PLL as clock source, the PLL VCO clock must be programmed
to output 432 MHz frequency (USBCLK = PLLVCO/PLLQ).
– PLLSAI clock (clocked by the HSE): If the USB uses the PLLSAI as clock source, the PLLSAI VCO clock must be programmed
to output 384 MHz frequency (USBCLK = PLLSAIVCO/PLLSAIP).
When the VCP application is started, the STM32 MCU is enumerated as serial communication port and is
configured in the same way (baudrate, data format, parity, stop bit) as it would configure a standard
COM port. The 7-bit data length with no parity control is NOT supported.
During enumeration phase, three communication pipes "endpoints" are declared in the CDC class
implementation (PSTN sub-class):
- 1 x Bulk IN endpoint for receiving data from STM32 device to PC host:
When data are received over UART they are saved in the buffer "UserTxBuffer". Periodically, in a
timer callback the state of the buffer "UserTxBuffer" is checked. If there are available data, they
are transmitted in response to IN token otherwise it is NAKed.
The polling period depends on "CDC_POLLING_INTERVAL" value.
- 1 x Bulk OUT endpoint for transmitting data from PC host to STM32 device:
When data are received through this endpoint they are saved in the buffer "UserRxBuffer" then they
are transmitted over UART using interrupt mode and in meanwhile the OUT endpoint is NAKed.
Once the transmission is over, the OUT endpoint is prepared to receive next packet in
HAL_UART_TxCpltCallback().
- 1 x Interrupt IN endpoint for setting and getting serial-port parameters:
When control setup is received, the corresponding request is executed in CDC_Itf_Control().
In this application, two requests are implemented:
- Set line: Set the bit rate, number of Stop bits, parity, and number of data bits
- Get line: Get the bit rate, number of Stop bits, parity, and number of data bits
The other requests (send break, control line state) are not implemented.
@note Receiving data over UART is handled by interrupt while transmitting is handled by DMA allowing
hence the application to receive data at the same time it is transmitting another data (full-
duplex feature).
The support of the VCP interface is managed through the ST Virtual COM Port driver available for
download from www.st.com.
@note The user has to check the list of the COM ports in Device Manager to find out the number of the
COM ports that have been assigned (by OS) to the VCP interface.
This application uses UART as a communication interface. The UART instance and associated resources
(GPIO, NVIC) can be tailored in "usbd_cdc_interface.h" header file according to your hardware
configuration. Moreover, this application can be customized to communicate with interfaces other than UART.
For that purpose a template CDC interface is provided in:
Middlewares/ST/STM32_USB_Device_Library/Class/CDC/Src directory.
In High Speed (HS) mode, enabling USB-DMA will result in data being sent only by multiple of 4 packet
sizes. This is due to the fact that USB DMA does not allow sending data from non word-aligned addresses.
For this specific application, it is advised to not enable the DMA capability unless required.
To run this application, the user can use one of the following configurations:
- Configuration 1:
Connect USB cable to host and UART (RS232) to a different host (PC or other device) or to same host.
In this case, you can open two hyperterminals to send/receive data to/from host to/from device.
- Configuration 2:
Connect USB cable to Host and connect UART TX pin to UART RX pin on the STM32F769I-EVAL board
(Loopback mode). In this case, you can open one terminal (relative to USB com port or UART com port)
and all data sent from this terminal will be received by the same terminal in loopback mode.
This mode is useful for test and performance measurements.
Hyperterminal configuration:
- Word Length = 8 Bits
- One Stop Bit
- None parity
- BaudRate = 115200
- flow control: None
@note Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds)
based on variable incremented in SysTick ISR. This implies that if HAL_Delay() is called from
a peripheral ISR process, then the SysTick interrupt must have higher priority (numerically lower)
than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
@note The application needs to ensure that the SysTick time base is always set to 1 millisecond
to have correct HAL operation.
For more details about the STM32Cube USB Device library, please refer to UM1734
"STM32Cube USB Device library".
@par USB Library Configuration
To select the appropriate USB Core to work with, user must add the following macro defines within the
compiler preprocessor (already done in the preconfigured projects provided with this application):
- "USE_USB_HS" when using USB High Speed (HS) Core
- "USE_USB_FS" when using USB Full Speed (FS) Core
- "USE_USB_HS" and "USE_USB_HS_IN_FS" when using USB High Speed (HS) Core in FS mode
@par Keywords
Connectivity, USB_Device, USB, Full Speed, High Speed, CDC, PSTN, UART, USB-to-RS232, Bridge, VCP, Com port,
@NoteIf the user code size exceeds the DTCM-RAM size or starts from internal cacheable memories (SRAM1 and SRAM2),that is shared between several processors,
then it is highly recommended to enable the CPU cache and maintain its coherence at application level.
The address and the size of cacheable buffers (shared between CPU and other masters) must be properly updated to be aligned to cache line size (32 bytes).
@Note It is recommended to enable the cache and maintain its coherence, but depending on the use case
It is also possible to configure the MPU as "Write through", to guarantee the write access coherence.
In that case, the MPU must be configured as Cacheable/Bufferable/Not Shareable.
Even though the user must manage the cache coherence for read accesses.
Please refer to the AN4838 “Managing memory protection unit (MPU) in STM32 MCUs”
Please refer to the AN4839 “Level 1 cache on STM32F7 Series”
@par Directory contents
- USB_Device/CDC_Standalone/Src/main.c Main program
- USB_Device/CDC_Standalone/Src/system_stm32f7xx.c STM32F7xx system clock configuration file
- USB_Device/CDC_Standalone/Src/stm32f7xx_it.c Interrupt handlers
- USB_Device/CDC_Standalone/Src/stm32f7xx_hal_msp.c HAL MSP module
- USB_Device/CDC_Standalone/Src/usbd_cdc_interface.c USBD CDC interface
- USB_Device/CDC_Standalone/Src/usbd_conf.c General low level driver configuration
- USB_Device/CDC_Standalone/Src/usbd_desc.c USB device CDC descriptor
- USB_Device/CDC_Standalone/Inc/main.h Main program header file
- USB_Device/CDC_Standalone/Inc/stm32f7xx_it.h Interrupt handlers header file
- USB_Device/CDC_Standalone/Inc/stm32f7xx_hal_conf.h HAL configuration file
- USB_Device/CDC_Standalone/Inc/usbd_conf.h USB device driver Configuration file
- USB_Device/CDC_Standalone/Inc/usbd_desc.h USB device MSC descriptor header file
- USB_Device/CDC_Standalone/Inc/usbd_cdc_interface.h USBD CDC interface header file
@par Hardware and Software environment
- This application runs on STM32F767xx/STM32F769xx/STM32F777xx/STM32F779xx devices.
- This application has been tested with STMicroelectronics STM32F769I-EVAL
evaluation boards and can be easily tailored to any other supported device
and development board.
- STM32F769I-EVAL Set-up
- Connect the STM32F769I_EVAL board to the PC through 'USB micro A-Male
to A-Male' cable to the connector:
- CN8 : to use USB High Speed (HS)
- CN13: to use USB Full Speed (FS)
- CN14: to use USB HS-IN-FS.
Note that some FS signals are shared with the HS ULPI bus, so some PCB rework is needed.
For more details, refer to section "USB OTG2 HS & FS" in STM32F769I_EVAL Evaluation Board
User Manual.
- Connect the STM32F769I-EVAL board to the PC (or to another evaluation board) through RS232 (USART)
serial cable CN7 (USART1) connector.
@note Make sure that jumper JP11 is fitted.
- For loopback mode test: remove RS232 cable on CN7 and connect directly USART TX and RX pins:
PA9 and PA10 (with a cable or a jumper)
@par How to use it ?
In order to make the program work, you must do the following :
- Open your preferred toolchain
- Rebuild all files and load your image into target memory
- In the workspace toolbar select the project configuration:
- STM327x6G_EVAL_USBH-HS: to configure the project for STM32F7xx devices using USB OTG HS peripheral
- STM327x6G_EVAL_USBH-FS: to configure the project for STM32F7xx devices using USB OTG FS peripheral
- STM327x6G_EVAL_USBH-HS-IN-FS: to configure the project for STM32F7xx devices and use USB OTG HS
peripheral In FS (using embedded PHY).
- Run the application
- Install the USB virtual COM port driver
- Find out the number of the COM port assigned to the STM32 CDC device
- Open a serial terminal application and start the communication
*/
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