Skip to content

Latest commit

 

History

History
167 lines (127 loc) · 10.4 KB

README.md

File metadata and controls

167 lines (127 loc) · 10.4 KB
Raw

Ux_Device_HID_CDC_ACM application description

This application provides an example of Azure RTOS USBX stack usage on STM32H747I-DISCO board, it shows how to develop a composite USB device communication class "HID" and "CDC_ACM" based application.

The application is designed to emulate a USB HID mouse device and USB-to-UART bridge following the Virtual COM Port (VCP) implementations, the code provides all required device descriptors framework and associated to both classes descriptor report to build a composite compliant USB HID_CDC_ACM device. At the beginning ThreadX calls the entry function tx_application_define(), at this stage, all USBx resources are initialized, the CDC_ACM and HID class driver is registered and the application creates 4 threads with the same priorities :

  • app_ux_device_thread_entry (Prio : 10; PreemptionPrio : 10) used to initialize USB_OTG HAL PCD driver and start the device.
  • usbx_cdc_acm_read_thread_entry (Prio : 20; PreemptionPrio : 20) used to read the received data from Virtual COM Port.
  • usbx_cdc_acm_write_thread_entry (Prio : 20; PreemptionPrio : 20) used to send the received data over UART .
  • usbx_hid_thread_entry (Prio : 20; PreemptionPrio : 20) used to send HID reports to move automatically the PC host machine cursor.

During enumeration phase, four communication pipes "endpoints" are declared in the CDC class and HID implementations :

  • 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 "UserTxBufferFS". Periodically, in a usbx_cdc_acm_write_thread_entry the state of the buffer "UserTxBufferFS" is checked. If there are available data, they are transmitted in response to IN token otherwise it is NAKed.

  • 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 "UserRxBufferFS" then they are transmitted over UART using DMA 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_RxCpltCallback().

  • 1 x Interrupt IN endpoint for setting and getting serial-port parameters: When control setup is received, the corresponding request is executed in USBD_CDC_ACM_ParameterChange.

In CDC_ACM 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.
  • 1 x Interrupt IN endpoint for setting the HID position: When the User Button is pressed the application calls the GetPointerData() API to update the mouse position (x, y) and send the report buffer through the ux_device_class_hid_event_set() API.

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.
  • The user has to check the list of HID and the COM ports in Device Manager to find out the HID device and the COM port number that have been assigned (by OS) to the VCP interface.

Expected success behavior

When plugged to PC host, the STM32H747I-DISCO must be properly enumerated a composite device as an HID, USB serial device and an STlink COM port. During the enumeration phase, the device must provide host with the requested descriptors (device descriptor, configuration descriptor, string descriptors). Those descriptors are used by host driver to identify the device capabilities. Once STM32H747I-DISCO USB device successfully completed the enumeration phase:

  • Connect USB cable to Host , Open two hyperterminals (USB com port and UART com port) to send/receive data to/from host to/from device.
  • When USER_Button is pressed, the device sends an HID report. Each report sent should move the PC host machine mouse cursor by one step.

Error behaviors

Host PC shows that USB device does not operate as designed (enumeration failed, for example PC cursor doesn't move or COM port enumeration failed).

Assumptions if any

User is familiar with USB 2.0 "Universal Serial BUS" specification and CDC_ACM class specification.

Known limitations

None.

Notes

  1. Some code parts can be executed in the ITCM-RAM (64 KB up to 256kB) which decreases critical task execution time, compared to code execution from Flash memory. This feature can be activated using '#pragma location = ".itcmram"' to be placed above function declaration, or using the toolchain GUI (file options) to execute a whole source file in the ITCM-RAM.
  2. If the application is using the DTCM/ITCM memories (@0x20000000/ 0x0000000: not cacheable and only accessible by the Cortex M7 and the MDMA), no need for cache maintenance when the Cortex M7 and the MDMA access these RAMs. If the application needs to use DMA (or other masters) based access or requires more RAM, then the user has to:
    • Use a non TCM SRAM. (example : D1 AXI-SRAM @ 0x24000000).
    • Add a cache maintenance mechanism to ensure the cache coherence between CPU and other masters (DMAs,DMA2D,LTDC,MDMA).
    • The addresses and the size of cacheable buffers (shared between CPU and other masters) must be properly defined to be aligned to L1-CACHE line size (32 bytes).
  3. It is recommended to enable the cache and maintain its coherence:
    • Depending on the use case it is also possible to configure the cache attributes using the MPU.
    • Please refer to the AN4838 "Managing memory protection unit (MPU) in STM32 MCUs".
    • Please refer to the AN4839 "Level 1 cache on STM32F7 Series and STM32H7 Series"

ThreadX usage hints

  • ThreadX uses the Systick as time base, thus it is mandatory that the HAL uses a separate time base through the TIM IPs.

  • ThreadX is configured with 100 ticks/sec by default, this should be taken into account when using delays or timeouts at application. It is always possible to reconfigure it, by updating the "TX_TIMER_TICKS_PER_SECOND" define in the "tx_user.h" file. The update should be reflected in "tx_initialize_low_level.S" file too.

  • ThreadX is disabling all interrupts during kernel start-up to avoid any unexpected behavior, therefore all system related calls (HAL, BSP) should be done either at the beginning of the application or inside the thread entry functions.

  • ThreadX offers the "tx_application_define()" function, that is automatically called by the tx_kernel_enter() API. It is highly recommended to use it to create all applications ThreadX related resources (threads, semaphores, memory pools...) but it should not in any way contain a system API call (HAL or BSP).

  • Using dynamic memory allocation requires to apply some changes to the linker file. ThreadX needs to pass a pointer to the first free memory location in RAM to the tx_application_define() function, using the "first_unused_memory" argument. This requires changes in the linker files to expose this memory location.

    • For EWARM add the following section into the .icf file:
    place in RAM_region    { last section FREE_MEM };
    • For MDK-ARM:
    either define the RW_IRAM1 region in the ".sct" file
or modify the line below in "tx_initialize_low_level.S to match the memory region being used
    LDR r1, =|Image$$RW_IRAM1$$ZI$$Limit|
    • For STM32CubeIDE add the following section into the .ld file:
    ._threadx_heap :
  {
     . = ALIGN(8);
     __RAM_segment_used_end__ = .;
     . = . + 64K;
     . = ALIGN(8);
   } >RAM_D1 AT> RAM_D1

    The simplest way to provide memory for ThreadX is to define a new section, see ._threadx_heap above.
In the example above the ThreadX heap size is set to 64KBytes.
The ._threadx_heap must be located between the .bss and the ._user_heap_stack sections in the linker script.
Caution: Make sure that ThreadX does not need more than the provided heap memory (64KBytes in this example).
Read more in STM32CubeIDE User Guide, chapter: "Linker script".
    • The "tx_initialize_low_level.S" should be also modified to enable the "USE_DYNAMIC_MEMORY_ALLOCATION" flag.

USBX usage hints

  • The DTCM (0x20000000) memory region should not be used by application in case USB DMA is enabled
  • Should make sure to configure the USB pool memory region with attribute "Non-Cacheable" to ensure coherency between CPU and USB DMA.

Keywords

RTOS, ThreadX, USBX, USBXDevice, USB_OTG, High Speed, CDC, HID, VCP, USART, DMA, Mouse.

Hardware and Software environment

  • This example runs on STM32H747xx devices

  • This example has been tested with STMicroelectronics STM32H747I-DISCO boards revision MB1520-H747I-B02 and can be easily tailored to any other supported device and development board.

  • STM32H747I-DISCO set-up:

    • Connect the STM32H747I-DISCO board CN1 to the PC through "MICRO-USB" to "Standard A" cable.
    • For VCP the configuration is dynamic for example it can be :
      • BaudRate = 115200 baud
      • Word Length = 8 Bits
      • Stop Bit = 1
      • Parity = None
      • Flow control = None

  • The USART1 interface available on PA9 and PA10 of the microcontroller are connected to ST-LINK MCU. By default the USART1 communication between the target MCU and ST-LINK MCU is enabled.

Its configuration is as follows: - BaudRate = 115200 baud - Word Length = 8 Bits - Stop Bit = 1 - Parity = None - Flow control = None

Note

  • When we configure the VCP baudrate under 9600 the USART1 baudrate shall be set to 9600.

How to use it ?

In order to make the program work, you must do the following :

  • Open your preferred toolchain
  • For each target configuration (Ux_Device_HID_CDC_ACM_CM4 first then Ux_Device_HID_CDC_ACM_CM7) :
    • Rebuild all files
    • Load images into target memory
  • After loading the two images, you have to reset the board in order to boot (Cortex-M7) and CPU2 (Cortex-M4) at once.
  • In the workspace toolbar select the project configuration:
  • Ux_Device_HID_CDC_ACM_CM7: to configure the project for STM32H747xx devices using USB OTG HS peripheral
  • Run the application