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Fx_uSD_File_Edit application description

This application provides an example of Azure RTOS FileX stack usage on STM32H735G-DK, it shows how to develop a basic SD card file operations application. The application is designed to handle SD card insertion/removal events, and depending on that state, it starts and stops file operations from and into the SD card.

The application is developed using HAL, so managing leds, SD initialisation or any SD card insertion/removal mechanisms are implemented using HAL drivers without any reference to BSP.

The main entry function, tx_application_define(), is called by ThreadX during kernel start. At this stage, all FileX resources are initialized, the SD card detection event is registered and drivers are initialized.

A single thread is created:

  • fx_app_thread (Prio : 10; PreemptionPrio : 10) used to initialize the SD driver and starting FileX's file operations.

A message queue is used to signal the SD card detection event to the fx_app_thread thread:

  • tx_msg_queue (Msg size : 1 (UINT); total messages : 16) used to notify the fx_app_thread about the SD card insertion status.

The fx_app_thread starts by checking whether the SD card is initially inserted or not. In the true case, it sends a message to the queue to ensure that the first iteration starts properly. The wait on the message queue blocks till it receives a new message about whether the SD card is inserted or removed. Interrupt callback for SD detection is registered and it is used to send the event information to the message queue.

The fx_app_thread uses FileX services to open the SD media for file operations and attempts to create file STM32.TXT. If the file exists already, it will be overwritten. Dummy content is then written into the file and it is closed. The file is opened once again in read mode and its content is checked if matches what was previously written.

It is possible to unplug/plug or replace the SD card without any need to reset the STM32H735G-DK. That is why MX_SDMMC1_SD_Init() should be public to initialize the newly plugged SD card.

Expected success behavior

  • A file named STM32.TXT should be visible in the root directory of the SD card.
  • A blinking green LED light marks the success of the file operations.

Error behaviors

  • On failure, the red LED should start blinking.
  • Error handler is called at the spot where the error occurred.

Assumptions if any

  • The SD card should be plugged prior to run the application.

Known limitations

Performing quick plug/unplug of SD card may trigger the Error_Handler() function.

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 calls (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, FAT32

Hardware and Software environment

  • This application runs on STM32H735xx devices.
  • This application 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