Microsoft's Azure RTOS ThreadX for Cortex-M7 Using the Green Hills Software Tools 1. Open the ThreadX Project Workspace In order to build the ThreadX library and the ThreadX demonstration first load the Azure RTOS Workspace azure_rtos_workspace.gpj, which is located inside the "example_build" directory. 2. Building the ThreadX run-time Library Building the ThreadX library is easy; simply select the MULTI project file tx.gpj and then select the build button. You should now observe the compilation and assembly of the ThreadX library. This project build produces the ThreadX library file tx.a. 3. Demonstration System The ThreadX demonstration is designed to execute under the MULTI environment on the Green Hills Cortex-M7 simulator. The instructions that follow describe how to get the ThreadX evaluation running under the MULTI Cortex-M7 simulation environment. Building the demonstration is easy; simply select the MULTI project file sample_threadx.gpj. At this point, select the "Project Build" button and observe the compilation, assembly, and linkage of the ThreadX demonstration application. After the demonstration is built, invoke the MULTI ARM simulator by selecting the simulator connection from within the sample_threadx.con connection file. Once connected to the simulator, select the "Debug" button. You should now observe the main function of sample_threadx.c. You are now ready to execute the ThreadX demonstration system. Select breakpoints and data watches to observe the execution of the sample_threadx.c application. 4. EventAnalyzer Demonstration To build a demonstration system that also logs events for the MULTI EventAnalyzer, perform the same steps as the regular demo, except build the ThreadX library with txe.gpj file and use the sample_threadx_el.gpj build file to build the demonstration. The resulting image will log all system events, which can then be displayed by the MULTI EventAnalyzer. 5. System Initialization The system entry point using the Green Hills tools is at the label _start. This is defined within the crt0.arm file supplied by Green Hills. In addition, this is where all static and global preset C variable initialization processing is called from. After the Green Hills startup function returns, ThreadX initialization is called. The main initialization function is _tx_initialize_low_level and is located in the file tx_initialize_low_level.arm. This function is responsible for setting up various system data structures, interrupt vectors, and the periodic timer interrupt source of ThreadX. In addition, _tx_initialize_low_level determines where the first available RAM memory address is located. This address is supplied to tx_application_define. By default, the first available RAM memory address is assumed to start at the beginning of the ThreadX section .free_mem. If changes are made to the sample_threadx.ld file, the .free_mem section should remain the last allocated section in the main RAM area. The starting address of this section is passed to tx_application_define. 6. 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-M7 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 r4 0x04 r5 0x08 r6 0x0C r7 0x10 r8 0x14 r9 0x18 r10 0x1C r11 0x20 r0 (Hardware stack starts here!!) 0x24 r1 0x28 r2 0x2C r3 0x30 r12 0x34 lr 0x38 pc 0x3C xPSR FPU Stack Frame (only interrupted thread with FPU enabled): Stack Offset Stack Contents 0x00 s0 0x04 s1 0x08 s2 0x0C s3 0x10 s4 0x14 s5 0x18 s6 0x1C s7 0x20 s8 0x24 s9 0x28 s10 0x2C s11 0x30 s12 0x34 s13 0x38 s14 0x3C s15 0x40 s16 0x44 s17 0x48 s18 0x4C s19 0x50 s20 0x54 s21 0x58 s22 0x5C s23 0x60 s24 0x64 s25 0x68 s26 0x6C s27 0x70 s28 0x74 s29 0x78 s30 0x7C s31 0x80 fpscr 0x84 r4 0x88 r5 0x8C r6 0x90 r7 0x94 r8 0x98 r9 0x9C r10 (sl) 0xA0 r11 0xA4 r0 (Hardware stack starts here!!) 0xA8 r1 0xAC r2 0xB0 r3 0xB4 r12 0xB8 lr 0xBC pc 0xC0 xPSR 7. 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 ThreadX run faster, you can change the tx.gpj project to disable debug information and enable the desired 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 before tx_api.h is included. 8. Interrupt Handling ThreadX provides complete and high-performance interrupt handling for Cortex-M7 targets. There are a certain set of requirements that are defined in the following sub-sections: 8.1 Vector Area The Cortex-M7 vectors start at the label __tx_vectors. The application may modify the vector area according to its needs. 8.2 Managed Interrupts A ThreadX managed interrupt is defined below. By following these conventions, the application ISR is then allowed access to various ThreadX services from the ISR. Here is the standard template for managed ISRs in ThreadX: .globl __tx_IntHandler __tx_IntHandler: PUSH {lr} BL _tx_thread_context_save /* Do interrupt handler work here */ B _tx_thread_context_restore 9. FPU Support By default, FPU support is disabled for each thread. If saving the context of the FPU registers is needed, the ThreadX library should be re-built with TX_ENABLE_FPU_SUPPORT defined. In addition, the following API call must be made from the context of the application thread - before the FPU usage: void tx_thread_fpu_enable(void); After this API is called in the application, FPU registers will be saved/restored for this thread if it is preempted via an interrupt. All other suspension of the this thread will not require the FPU registers to be saved/restored. To disable FPU register context saving, simply call the following API: void tx_thread_fpu_disable(void); 10. 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: 05/19/2020 Initial ThreadX version of Cortex-M7/Green Hills port. Copyright(c) 1996-2020 Microsoft Corporation https://azure.com/rtos