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Microsoft's Azure RTOS ThreadX for ARMv7-M
(Cortex-M3, Cortex-M4, Cortex-M7)
Using ARM Compiler 5 (AC5)
1. Building the ThreadX run-time Library
Navigate to the "example_build" directory. Ensure that
you have setup your path and other environment variables necessary for the AC5
compiler. At this point you may run the build_threadx.bat batch file. This will
build the ThreadX run-time environment in the "example_build" directory.
You should observe assembly and compilation of a series of ThreadX source
files. At the end of the batch file, they are all combined into the
run-time library file: tx.a. This file must be linked with your
application in order to use ThreadX.
2. Demonstration System
The ThreadX demonstration is designed to execute under the ARM DS Cortex-M
simulator.
Building the demonstration is easy; simply execute the build_threadx_sample.bat
batch file while inside the "example_build" directory.
You should observe the compilation of sample_threadx.c (which is the demonstration
application) and linking with tx.a. The resulting file sample_threadx.axf
is a binary file that can be downloaded and executed on the ARM DS Cortex-M
simulator.
3. System Initialization
The entry point in ThreadX for the Cortex-M using AC5 tools is at label
__main. This is defined within the AC5 compiler's startup code. In
addition, this is where all static and global pre-set C variable
initialization processing takes place.
The ThreadX tx_initialize_low_level.s file is responsible for setting up
various system data structures, the vector area, and a periodic timer interrupt
source.
In addition, _tx_initialize_low_level 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.
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-M 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.
Non-FPU Stack Frame:
Stack Offset Stack Contents
0x00 lr Interrupted lr (lr at time of PENDSV)
0x04 r4 Software stacked GP registers
0x08 r5
0x0C r6
0x10 r7
0x14 r8
0x18 r9
0x1C r10
0x20 r11
0x24 r0 Hardware stacked registers
0x28 r1
0x2C r2
0x30 r3
0x34 r12
0x38 lr
0x3C pc
0x40 xPSR
FPU Stack Frame (only interrupted thread with FPU enabled):
Stack Offset Stack Contents
0x00 lr Interrupted lr (lr at time of PENDSV)
0x04 s16 Software stacked FPU registers
0x08 s17
0x0C s18
0x10 s19
0x14 s20
0x18 s21
0x1C s22
0x20 s23
0x24 s24
0x28 s25
0x2C s26
0x30 s27
0x34 s28
0x38 s29
0x3C s30
0x40 s31
0x44 r4 Software stacked registers
0x48 r5
0x4C r6
0x50 r7
0x54 r8
0x58 r9
0x5C r10
0x60 r11
0x64 r0 Hardware stacked registers
0x68 r1
0x6C r2
0x70 r3
0x74 r12
0x78 lr
0x7C pc
0x80 xPSR
0x84 s0 Hardware stacked FPU registers
0x88 s1
0x8C s2
0x90 s3
0x94 s4
0x98 s5
0x9C s6
0xA0 s7
0xA4 s8
0xA8 s9
0xAC s10
0xB0 s11
0xB4 s12
0xB8 s13
0xBC s14
0xC0 s15
0xC4 fpscr
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-M
targets. There are a certain set of requirements that are defined in the
following sub-sections:
6.1 Vector Area
The Cortex-M vectors start at the label __tx_vectors. The application may modify
the vector area according to its needs.
6.2 Managed Interrupts
ISRs for Cortex-M 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:
EXPORT your_assembly_isr
your_assembly_isr
PUSH {r0, lr}
; ISR processing goes here, including any needed function calls.
POP {r0, lr}
BX lr
7. FPU Support
ThreadX for Cortex-M supports automatic ("lazy") VFP support, which means that applications threads
can simply use the VFP and ThreadX automatically maintains the VFP registers as part of the thread
context - no additional setup by the application.
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:
06-02-2021 Initial ThreadX version 6.1.7 for Cortex-M using AC5 tools.
Copyright(c) 1996-2021 Microsoft Corporation
https://azure.com/rtos
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