Tx_MPU Application Description
- This application provides an example of Azure RTOS ThreadX stack
usage, it shows how to develop an application using the ThreadX Module
feature.
- It demonstrates how to load, start and unload modules.
- In addition, it shows how ThreadX memory protection on modules using
the Memory Protection Unit (MPU).
This project is composed of two sub-projects:
- Tx_Module_Manager : ThreadX Module Manager code that load and start
the module dynamically at runtime.
- Tx_Module : ThreadX Module code that is to be loaded and started by
the module manager dynamically at runtime.
At the module manager stage, the main entry function
tx_application_define() is called by ThreadX during kernel start, the
application creates 1 thread and 1 message queue:
- ModuleManager (Prio : 4; Preemption Threshold : 4)
- ResidentQueue (Size : 16 * ULONG)
ModuleManager thread uses the ThreadX Module Manager APIs to
configure, load and start the expected module. ResidentQueue is used to
synchronize operations between Module Manager and the loaded Module.
At the module stage, the main entry function default_module_start()
is called by ThreadX during module start, the application creates 1
thread:
- MainThread (Prio : 2; Preemption Threshold : 2)
MainThread is expected to execute data read and write operations
to/from user-defined Shared Memory regions. Memory protection is then
demonstrated by trapping the Module’s attempt at writing to the shared
Read Only region. A Memory Fault is then expected before the unload of
the module and the module manager continues to run correctly.
Expected success behavior
- LED_GREEN toggles every 500ms.
- Information regarding the module processing progress printed to the
serial port.
Error behaviors
- Error message is printed on the HyperTerminal
Assumptions if any
Known limitations
Notes
- By default ThreadX module configures the memory as shareable which
not supported by stm32C0, the following flags should be overridden in
the txm_module_user file as below :
- TXM_MODULE_MPU_CODE_ACCESS_CONTROL 0x06030000
- TXM_MODULE_MPU_DATA_ACCESS_CONTROL 0x13030000
- TXM_MODULE_MPU_SHARED_ACCESS_CONTROL 0x12030000
The preprocessor flag “TXM_MODULE_INCLUDE_USER_DEFINE_FILE” should be
added in the C preprocessor list to take into account the above
change.
- A preamble is required with each Module to expose the module
configuration to the Module Manager. Particularly the preamble contains
information such as the module unique ID and attributes. Module
Properties (attributes) is a 32bit word, laid out as:
- Bits 31-24: Compiler ID 0 -> IAR 1 -> ARM 2 -> GNU
- Bits 23-3: Reserved
- Bit 2: 0 -> Disable shared/external memory access 1 -> Enable
shared/external memory access
- Bit 1: 0 -> No MPU protection 1 -> MPU protection (must have
user mode selected - bit 0 set)
- Bit 0: 0 -> Privileged mode execution 1 -> User mode
execution
For this application demonstrating MPU memory protection on modules,
the attributes should be set as follows:
- Shared memory access is allowed.
- MPU protection is enabled.
- User mode is set for the module
The above configuration results in an attributes word equals
0x00000007
All C files in a module must #define TXM_MODULE prior to
including txm_module.h. Doing so remaps the ThreadX API calls to the
module-specific version of the API that invokes the dispatch function in
the resident Module Manager to perform the call to the actual API
function.
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 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.
Keywords
- RTOS, ThreadX, Threading, Message Queue, Module Manager, Module,
MPU
Hardware and Software
environment
This application runs on STM32C071xx devices.
This application has been tested with STMicroelectronics
NUCLEO-C071RB board MB2046 Rev. B01 and can be easily tailored to
any other supported device and development board.
This application uses UART2 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 ?
In order to make the program work, you must do the following
:
Open Multi-projects workspace using your pereferred IDE
Rebuild Tx_Module project (Tx_Module will be loaded automatically
by Tx_Module_Manager at address defined by
“MODULE_FLASH_ADDRESS”)
Rebuild Tx_Module_Manager project
Set the Tx_Module_Manager as active application
Run the example