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Ux_Device_CDC_ECM application description

This application provides an example of Azure RTOS CDC_ECM stack usage on STM32H7S78-DK board, it shows how to run web HTTP server based application stack over USB interface. The application is designed to load files and web pages stored in SD card using a web HTTP server through USB interface using CDC_ECM class, the code provides all required features to build a compliant web HTTP Server. The main entry function tx_application_define() is called by ThreadX during kernel start, at this stage, the USBX initializes the network layer through USBx class (CDC_ECM) also the FileX and the NetXDuo system are initialized, the NX_IP instance and the web HTTP server are created and configured, then the application creates two main threads

  • usbx_app_thread_entry (Prio : 10; PreemptionPrio : 10) used to initialize USB_OTG HAL PCD driver and start the device.
  • nx_server_thread_entry (Prio :10; PreemptionPrio :10) used to assign a dynamic IP address, open the SD card driver as a FileX media and start the web HTTP server. Fetching a dynamic IP address to the STM32H7S78-DK board is a step blocking until an IP address is obtained. Once the server is started, the user's browser can load web pages as index.html and STM32H7RSxxLED.html.

Expected success behavior

When an SD card is inserted into the STM32H7S78-DK SD card reader and the board is powered up and connected to DHCP enabled Ethernet network. Then the web page can be loaded on the web browser after entring the url http://@IP/index.html also the user can switch to STM32H7RSxxLED.html page to toggle the green LED. An example of web pages is provided for testing the application that can be found under "USBX/Ux_Device_CDC_ECM/Web_Content/"

Error behaviors

If the web HTTP server is not successfully started, the red LED should start blinking. In case of other errors, the web HTTP server does not operate as designed (Files stored in the SD card are not loaded in the web browser).

Assumptions if any

The uSD card must be plugged before starting the application. The board must be in a DHCP Ethernet network.

Known limitations

Hotplug is not implemented for this example, that is, the SD card is expected to be inserted before application running.

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.

FileX/LevelX usage hints

  • FileX sd driver is using the DMA, thus the DTCM (0x20000000) memory should not be used by the application, as it is not accessible by the SD DMA.
  • When calling the fx_media_format() API, it is highly recommended to understand all the parameters used by the API to correctly generate a valid filesystem.
  • FileX is using data buffers, passed as arguments to fx_media_open(), fx_media_read() and fx_media_write() API it is recommended that these buffers are multiple of sector size and "32 bytes" aligned to avoid cache maintenance issues.
  • 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, USBXDevice, CDC_ECM, Network, NetxDuo, FileX, File ,SDMMC, UART

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.
  • This application uses USART4 to display logs, the hyperterminal configuration is as follows:
    • BaudRate = 115200 baud
    • Word Length = 8 Bits
    • Stop Bit = 1
    • Parity = none
    • Flow control = None

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
  • Under host linux desktop go to the "Ethernet Network" and configure the IPV4 method to "Shared to other computers".