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Microsoft's Azure RTOS ThreadX for Cortex-M0
Using the IAR Tools
1. Building the ThreadX run-time Library
Building the ThreadX library is easy. First, open the Azure RTOS workspace
azure_rtos.eww. Next, make the TX project the "active project" in the
IAR Embedded Workbench and select the "Make" button. You should observe
assembly and compilation of a series of ThreadX source files. This
results in the ThreadX run-time library file tx.a, which is needed by
the application.
2. Demonstration System
The ThreadX demonstration is designed to execute under the IAR
Windows-based Cortex-M0 simulator.
Building the demonstration is easy; simply make the sample_threadx.ewp project
the "active project" in the IAR Embedded Workbench and select the
"Make" button.
You should observe the compilation of sample_threadx.c (which is the demonstration
application) and linking with tx.a. The resulting file sample_threadx.out is a
binary file that can be downloaded and executed on IAR's Cortex-M0 simulator.
3. System Initialization
The entry point in ThreadX for the Cortex-M0 using IAR tools is at label
__iar_program_start. This is defined within the IAR compiler's startup code.
In addition, this is where all static and global preset C variable
initialization processing takes place.
The ThreadX tx_initialize_low_level.s file is responsible for setting up
various system data structures, and a periodic timer interrupt source.
By default, the vector area is defined at the top of cstartup_M.s, which is
a slightly modified from the base IAR file.
The _tx_initialize_low_level function inside of tx_initialize_low_level.s
also determines the first available address for use by the application, which
is supplied as the sole input parameter to your application definition function,
tx_application_define. To accomplish this, a section is created in
tx_initialize_low_level.s called FREE_MEM, which must be located after all
other RAM sections in memory.
4. Register Usage and Stack Frames
The following defines the saved context stack frames for context switches
that occur as a result of interrupt handling or from thread-level API calls.
All suspended threads have the same stack frame in the Cortex-M0 version of
ThreadX. The top of the suspended thread's stack is pointed to by
tx_thread_stack_ptr in the associated thread control block TX_THREAD.
Stack Offset Stack Contents
0x00 LR Interrupted LR (LR at time of PENDSV)
0x04 r4
0x08 r5
0x0C r6
0x10 r7
0x14 r8
0x18 r9
0x1C r10 (sl)
0x20 r11
0x24 r0 (Hardware stack starts here!!)
0x28 r1
0x2C r2
0x30 r3
0x34 r12
0x38 lr
0x3C pc
0x40 xPSR
5. Improving Performance
The distribution version of ThreadX is built without any compiler
optimizations. This makes it easy to debug because you can trace or set
breakpoints inside of ThreadX itself. Of course, this costs some
performance. To make it run faster, you can change the ThreadX library
project to enable various compiler optimizations.
In addition, you can eliminate the ThreadX basic API error checking by
compiling your application code with the symbol TX_DISABLE_ERROR_CHECKING
defined.
6. Interrupt Handling
ThreadX provides complete and high-performance interrupt handling for Cortex-M3
targets. There are a certain set of requirements that are defined in the
following sub-sections:
6.1 Vector Area
The Cortex-M3 vectors start at the label __vector_table and is defined in cstartup_M.s.
The application may modify the vector area according to its needs.
6.2 Managed Interrupts
ISRs for Cortex-M using the IAR tools can be written completely in C (or assembly
language) without any calls to _tx_thread_context_save or _tx_thread_context_restore.
These ISRs are allowed access to the ThreadX API that is available to ISRs.
ISRs written in C will take the form (where "your_C_isr" is an entry in the vector table):
void your_C_isr(void)
{
/* ISR processing goes here, including any needed function calls. */
}
ISRs written in assembly language will take the form:
PUBLIC your_assembly_isr
your_assembly_isr:
PUSH {lr}
; ISR processing goes here, including any needed function calls.
POP {r0}
MOV lr, r0
BX lr
7. IAR Thread-safe Library Support
Thread-safe support for the IAR tools is easily enabled by building the ThreadX library
and the application with TX_ENABLE_IAR_LIBRARY_SUPPORT. Also, the linker control file
should have the following line added (if not already in place):
initialize by copy with packing = none { section __DLIB_PERTHREAD }; // Required in a multi-threaded application
The project options "General Options -> Library Configuration" should also have the
"Enable thread support in library" box selected.
8. Revision History
For generic code revision information, please refer to the readme_threadx_generic.txt
file, which is included in your distribution. The following details the revision
information associated with this specific port of ThreadX:
04-02-2021 Release 6.1.6 changes:
tx_port.h Updated macro definition
03-02-2021 The following files were changed/added for version 6.1.5:
tx_thread_schedule.s Added low power feature
09-30-2020 Initial ThreadX version 6.1 for Cortex-M0 using IAR's ARM tools.
Copyright(c) 1996-2020 Microsoft Corporation
https://azure.com/rtos
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