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Fx_MultiAccess application description

This application provides an example of Azure RTOS FileX stack usage on STM32H735G-DK board, it demonstrates the FileX's concurrent file access capabilities. The application is designed to execute file operations on the SD card device, the code provides all required software code for handling SD card I/O operations.

The application starts by calling the ThreadX's initialization routine which creates multithreaded environment for starting the concurrent FileX's two main threads that handle file operations. At this stage, all FileX resources are created, the SDIO driver is initialized and the application creates 3 threads with the same priorities:

  • fx_app_thread (Prio : 10; PreemptionPrio : 10) used to initialize the SD card driver and opening it as a FileX Media.
  • fx_thread_one (Prio : 10; PreemptionPrio : 10) used to create, write and read operations for file fx_file_one.
  • fx_thread_two (Prio : 10; PreemptionPrio : 10) used to create, write and read operations for file fx_file_two.

Note: A FAT32 compatible SD card is expected to be used with this example. The program will start file operations without formatting the media, so all user related files are kept.

Expected success behavior

  • When an SD card is inserted into the STM32H735G-DK SD card reader and the board is powered up, the application starts file operations.
  • During the start phase, the main thread starts by opening the SD card using FileX media open service. Upon successful opening of the media and its underlying FAT32 file system, the main thread starts the two file operations threads, fx_thread_one and fx_thread_two. The two threads then start file operations, each at a different file.
  • This demonstrates the concurrent access handling capabilities of FileX, without the need for an external access-aribitration locks.
  • Successful operation is marked by a toggling LED_GREEN light.

Error behaviors

On failure, the LED_RED starts toggling while the LED_GREEN is switched OFF.

Assumptions if any

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

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 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 call (HAL) 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).

  • 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.

Keywords

RTOS, ThreadX, FileX, File system, SDMMC, SDIO, FAT32

Hardware and Software environment

  • This example runs on STM32H735xx devices.
  • This example has been tested with STMicroelectronics STM32H735G-DK boards revision: MB1520-H735I-B02 and can be easily tailored to any other supported device and development board.

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
  • Run the application