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Ux_Device_MSC application description

This application provides an example of Azure RTOS USBX stack usage on STM32H7S78-DK board, it shows how to develop USB device mass storage class based application. The application is designed to emulate a USB MSC device, the code provides all required device descriptors framework and the associated class descriptor report to build a compliant USB MSC device.

At the beginning ThreadX calls the entry function tx_application_define(), at this stage, all USBx resources are initialized, the mass storage class driver is registered and the application creates one thread:

  • app_ux_device_thread_entry (Prio : 10; PreemptionPrio : 10) used to initialize USB OTG HAL PCD driver and start the device.

In addition two callback functions are needed for the USBX mass storage class device:

  • USBD_STORAGE_Read used to read data through DMA from the mass storage device.
  • USBD_STORAGE_Write used to write data through DMA into the mass storage device.

Expected success behavior

When plugged to PC host, the STM32H7S78-DK should enumerate as a USB MSC device. During the enumeration phase, device must provide host with the requested descriptors (device descriptor, configuration descriptor, string descriptors). Those descriptors are used by the host driver to identify the device capabilities. Once the STM32H7S78-DK USB device successfully completed the enumeration phase, a new removable drive appears in the system window and write/read/format operations can be performed as with any other removable drive.

Error behaviors

Host PC shows that USB device does not operate as designed (MSC enumeration fails, the new removable drive appears but read, write or format operations fail).

Assumptions if any

  • USB cable should not be unplugged during enumeration and driver installation.
  • SD card should be inserted before application is started.

Known limitations

The Eject operation is not supported yet by MSC class.

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 in the "tx_user.h", the "TX_TIMER_TICKS_PER_SECOND" define,but this 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 require 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, USBXDevice, Device, USB_OTG, Full Speed, MSC, Mass Storage, SD Card, DMA, SDMMC

Hardware and Software environment

  • This example runs on STM32H7S7L8xx devices.
  • This example 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.

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 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