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Ux_Host_CDC_ACM application description

This application provides an example of Azure RTOS USBX stack usage .

The application is designed to behave as USB CDC_ACM Host, the code provides required requests to properly enumerate CDC devices, CDC_ACM class APIs to send or receive data and display data on UART HyperTerminal.

The main entry function tx_application_define() is then called by ThreadX during kernel start, at this stage, all USBx resources are initialized. The application creates 3 threads with different priorities:

  • app_ux_host_thread_entry (Priority : 10; Preemption threshold : 10) used to initialize USB OTG HAL HCD driver and start the Host.
  • cdc_acm_send_app_thread_entry (Priority : 30; Preemption threshold : 30) used to send data from host to device.
  • cdc_acm_recieve_app_thread_entry (Priority : 30; Preemption threshold : 30) used to receive data from the device.

Expected success behavior

  • When a CDC device is plugged to STM32H7S78-DK board, a message will be displayed on the UART HyperTerminal (STlink VCP) showing the Vendor ID and Product ID of the attached device. The host must be able to properly decode CDC_ACM class request data sent by the device. After enumeration phase, a message will indicate that the device is ready for use.
  • The sent/received data are displayed on respective Hyperterminals.

Error behaviors

Errors are detected (such as unsupported device, enumeration Fail) and the corresponding message is displayed on the HyperTerminal.

Assumptions if any

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

Known limitations

None

Notes

  1. This application runs from the external flash memory. It is launched from a first boot stage and inherits from this boot project configuration (caches, MPU regions [region 0 and 1], system clock at 600 MHz and external memory interface at the highest speed). Note that the boot part is automatically downloaded from the IDE environment via the board boot binary under Binary/Boot_XIP.hex file.

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

Connectivity, USBX Host, USBPD, ThreadX, USB, CDC_ACM, UART, USART

Hardware and Software environment

  • This application runs on STM32H7S7L8xx devices.

  • This application has been tested with STMicroelectronics STM32H7S78-DK boards revision MB1736-H7S7L8-C01 and can be easily tailored to any other supported device and development board.

  • STM32H7S78-DK set-up:

    • Plug the USB CDC_ACM device into the STM32H7S78-DK board through "TYPE-C" to "Standard A" cable to the connector:
      • CN18 : to use USB OTG IP in high speed (HS)
    • Connect ST-Link cable to the PC USB port to display data on the HyperTerminal.

    A virtual COM port will then appear in the HyperTerminal:

    • Hyperterminal configuration
      • Data Length = 8 Bits
      • One Stop Bit
      • No parity
      • BaudRate = 115200 baud
      • Flow control: None

    A second virtual COM port will then appear in the HyperTerminal when plugging the device:

    • Hyperterminal configuration

      • Data Length = 8 Bits
      • One Stop Bit
      • No parity
      • BaudRate = 9600 baud
      • Flow control: None

    • To send data from the USB CDC_ACM Host use the user push-button and data will be received and displayed in the HyperTerminal connected to the CDC ACM Device.

How to use it ?

To configure STM32CubeIDE Debug Configuration, you must do the following :

1. Add the adequate external loader (MX66UW1G45G_STM32H7S78-DK.stldr file) in Project->Debugger Configuration
2. Add in the startup the Boot_XIP.elf file in Project->Debugger Configuration
3. Move up the application in the startup

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
  • Run the application
  • Click the user button to send predefined data from the Host board to the CDC device.

Notes

  • 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 Stlink VCP.
  • The application uses the external HSE clock as USB source clock.