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