![§ For each task:
§ YOU assign a priority based on its importance
§ Requires its own Stack
§ Manages its own variables, arrays and structures
§ Is typically an infinite loop
§ Possibly manages I/O devices
§ Contains YOUR application code
Tasks
CPU_STK MyTaskStk[MY_TASK_STK_SIZE]; // Task Stack
void MyTask (void *p_arg) // Task Code
{
Local Variables;
Task initialization;
while (1) { // Infinite Loop (Typ.)
Wait for Event;
Perform task operation; // Do something useful
}
}
Task
(Priority)
Stack
(RAM) Variables
Arrays
Structures
(RAM)
I/O
Device(s)
(Optional)
silabs.com | @silabs](https://image.slidesharecdn.com/introtortos-240903060342-71b7e32c/85/Intro-To-RTOS-by-Silicon-labs-covering-fundamentals-7-320.jpg)
![§ You must tell the RTOS about the existence of a task:
§ The RTOS provides a special API: OSTaskCreate() (or equivalent)
§ The RTOS assigns the task:
§ Its own set of CPU registers
§ A Task Control Block (TCB)
Creating a Task
Task
(Priority)
Stack
(RAM) Variables
Arrays
Structures
(RAM)
CPU
Registers
(CPU+FPU+MPU)
I/O
Device(s)
(Optional)
TCB
(RAM)
void OSTaskCreate (MyTask, // Address of code
&MyTaskStk[0], // Base of stack
MY_TASK_STK_SIZE,// Size of stack
MY_TASK_PRIO, // Task priority
:
:);
silabs.com | @silabs](https://image.slidesharecdn.com/introtortos-240903060342-71b7e32c/85/Intro-To-RTOS-by-Silicon-labs-covering-fundamentals-8-320.jpg)
Intro To RTOS by Silicon labs covering fundamentals
- 1. J E A N L A B R O S S E | D I S T I N G U I S H E D E N G I N E E R E M B E D D E D W O R L D : F E B R U A R Y 2 6 - 2 8 , 2 0 1 9 Everything You Need to Know about RTOSs in 30 Minutes
- 2. § An RTOS is software that manages the time and resources of a CPU § Application is split into multiple tasks § The RTOS’s job is to run the most important task that is ready-to-run § On a single CPU, only one task executes at any given time An RTOS Allows Multitasking RTOS (Code) Task (Code+Data+Stack) Task (Code+Data+Stack) Task (Code+Data+Stack) Task (Code+Data+Stack) High Priority Low Priority Events Signals/Messages from Tasks or ISRs CPU+FPU+MPU (8, 16, 32 or 64-bit) Select Highest Priority Task Tasks that are ready-to-run silabs.com | @silabs
- 3. An RTOS Provides Services To Your Application CPU + FPU (opt) + MPU (opt) Tasks OSTaskCreate(..) OSTaskDel(..) OSTaskSuspend(..) OSTaskResume(..) OSTaskChangePrio() : : Semaphores OSSemCreate(..) OSSemDel(..) OSSemPend(..) OSSemPost(..) : : OSFlagCreate(..) OSFlagDel(..) OSFlagPend(..) OSFlagPost(..) : : Event Flags Mutexes OSMutexCreate(..) OSMutexDel(..) OSMutexPend(..) OSMutexPost(..) : : OSQCreate(..) OSQDel(..) OSQPend(..) OSQPost(..) : : Queues OSTmrCreate(..) OSTmrDel(..) OSTmrStart(..) OSTmrStop(..) : : Timers Memory Blocks OSMemCreate(..) OSMemDel(..) OSMemGet(..) OSMemPut(..) : : RTOS Application (Code + Data) Optional Middleware (Code + Data) (TCP/IP, GUI, File System, USB Stacks, Bluetooth, Etc.) Time OSTimeDly(..) OSTimeDlyHMSM(..) OSTimeDlyResume(..) OSTimeGet(..) OSTimeSet(..) : : silabs.com | @silabs
- 4. Benefits of Using an RTOS § Allows you to split and prioritize the application code § The RTOS always runs the highest priority task that is ready § Adding low-priority tasks don’t affect the responsiveness of high priority tasks § Tasks wait for events § Avoids polling § RTOSs make it easy to add middleware components § TCP/IP stack § USB stacks § File System § Graphical User Interface (GUI) § Etc. silabs.com | @silabs
- 5. Benefits of Using an RTOS § Creates a framework for developing applications § Facilitate teams of multiple developers § It’s possible to meet all the deadlines of an application § Rate Monotonic Analysis (RMA) could be used to determine schedulability § Most RTOSs have undergone thorough testing § Some are third-party certifiable, and even certified (DO-178B, IEC-61508, IEC-62304, etc.) § It’s unlikely that you will find bugs in RTOSs § RTOSs typically support many different CPU architectures § Very easy to add power management silabs.com | @silabs
- 6. Drawbacks of Using an RTOS § The RTOS itself is code and thus requires more Flash § Typically between 6-20K bytes § An RTOS requires extra RAM § Each task requires its own stack § The size of each task depends on the application § Each task needs to be assigned a Task Control Block (TCB) § About 32 to 128 bytes of RAM § About 256 bytes for the RTOS variables § You have to assign task priorities § Deciding on what priority to give tasks is not always trivial § The services provided by the RTOS consume CPU time § Overhead is typically 2-10% of the CPU cycles § There is a learning curve associated with the RTOS you select silabs.com | @silabs
- 7. § For each task: § YOU assign a priority based on its importance § Requires its own Stack § Manages its own variables, arrays and structures § Is typically an infinite loop § Possibly manages I/O devices § Contains YOUR application code Tasks CPU_STK MyTaskStk[MY_TASK_STK_SIZE]; // Task Stack void MyTask (void *p_arg) // Task Code { Local Variables; Task initialization; while (1) { // Infinite Loop (Typ.) Wait for Event; Perform task operation; // Do something useful } } Task (Priority) Stack (RAM) Variables Arrays Structures (RAM) I/O Device(s) (Optional) silabs.com | @silabs
- 8. § You must tell the RTOS about the existence of a task: § The RTOS provides a special API: OSTaskCreate() (or equivalent) § The RTOS assigns the task: § Its own set of CPU registers § A Task Control Block (TCB) Creating a Task Task (Priority) Stack (RAM) Variables Arrays Structures (RAM) CPU Registers (CPU+FPU+MPU) I/O Device(s) (Optional) TCB (RAM) void OSTaskCreate (MyTask, // Address of code &MyTaskStk[0], // Base of stack MY_TASK_STK_SIZE,// Size of stack MY_TASK_PRIO, // Task priority : :); silabs.com | @silabs
- 9. RTOSs Are Event Driven Task Task Task Task Task High Priority Low Priority void EachTask (void) { Task initialization; while (1) { Setup to wait for event; Wait for MY event to occur; Perform task operation; } } Event Occurs Wait For Event § Only the highest-priority Ready task can execute § Other tasks will run when the current task decides to waits for its event § Ready tasks are placed in the RTOS’s Ready List § Tasks waiting for their event are placed in the Event Wait List … Task Task Task silabs.com | @silabs
- 10. Tasks Waiting for Events Are Placed in a Wait List Task waiting for DMA to complete DMA Completion Semaphore Printer Access Mutex Task waiting to access printer Task waiting to access printer Task waiting to access printer High Priority Low Priority Tick List (Delta List) Task waiting for time to expire Task waiting for time to expire Task waiting for time to expire Shortest Delay or Timeout Longest Delay or Timeout silabs.com | @silabs
- 11. RTOSs Are Preemptive High Priority Task Low Priority Task Low Priority Task Event Occurs Signal Task RTOS Resumes Task RTOS Resumes Task Wait For Event ISR void Low_Prio_Task (void) { Task initialization; while (1) { Setup to wait for event; Wait for event to occur; Perform task operation; } } void High_Prio_Task (void) { Task initialization; while (1) { Setup to wait for event; Wait for event to occur; Perform task operation; } } void ISR (void) { Entering ISR; Perform Work; Signal or Send Message to Task; Perform Work; // Optional Leaving ISR; } Time RTOS Overhead silabs.com | @silabs
- 12. Interrupts Must Notify the RTOS § Oftentimes, interrupts are events that tasks are wait for § Interrupts are more important than tasks § Assuming, of course, that interrupts are enabled § Kernel Aware (KA) ISRs: § Need to notify the RTOS of ISR entry and exit § Allows for nesting ISRs and avoid multiple scheduling § ISRs can be written directly in C on Cortex-M CPUs void MyISR (void) { Entering ISR; : Signal or send a message to a MyTask; : Leaving ISR; } Task Task Event Occurs ISR Level 3 RTOS resumes which task? Signal OR? Task ISR Level 2 ISR Level 1 Exit Enter Event Occurs Event Occurs No scheduling No scheduling Scheduling silabs.com | @silabs
- 13. A Context Switch Occurs When the RTOS Decides to Run Another Task Example using Cortex-M4 CPU FPU Task Stack (RAM) Task Stack (RAM) CPU Registers + FPU Registers Context Switch Save Restore 1 2 Task Control Block (TCB) Task Control Block (TCB) silabs.com | @silabs
- 14. Most RTOSs Have a Periodic Time Source § Most RTOS have a time-based interrupt § Called the System Tick or Clock Tick § Requires a hardware timer § The System Tick is used to provide coarse: § Delay (or sleep) § Timeouts on Wait for Event RTOS APIs § A System Tick is not mandatory! § If you don’t need time delays or timeouts you can remove it § Typically interrupts at regular intervals § Not power-efficient § Dynamic tick (a.k.a. tick suppression) is more efficient § Requires reconfiguring the tick timer at each interrupt Typical RTOS Tick Dynamic RTOS Tick 5 ms 17 ms 5 ms 3 ms Typ. 1 ms silabs.com | @silabs
- 15. RTOS Services – Time Delays (i.e. Sleep) § A task can put itself to sleep by calling RTOS APIs: § OSTimeDly() // Delay for N ticks § OSTimeDlyHMSM() // Delay for Hours, Minutes, Seconds, Milliseconds § Can be used to wake up a task at regular intervals § Control loops § Updating a display § Scanning a keyboard § Letting other tasks a chance to run § Etc. Task void Task (void) { Task initialization; while (1) { Sleep for ‘N’ ticks; Do work; } } N Ticks silabs.com | @silabs
- 16. RTOS Services – Sharing a Resource Using a Mutex § What is a resource? § Shared memory, variables, arrays, structures § I/O devices § RTOSs typically provide resource sharing APIs § Mutex have built-in priority inheritance § Eliminates unbounded priority inversions § There could be multiple mutexes in a system § Each protecting access to a different resource Task Task Task Shared Resource (Memory or I/O) Mutex Acquire Relinquish 1 2 Access 3 void EachTask (void) { Task initialization; while (1) { : : Acquire Mutex; Access the resource; Relinquish the Mutex; : } } Timeout OSMutexPost() OSMutexPend() silabs.com | @silabs
- 17. RTOS Services – Signaling a Task Using a Semaphore § Semaphores can be used to signal a task § Called from ISR or Task § Does not contain data ISR Task Semaphore Signal Wait void TaskEventISR (void) { Clear interrupt; Signal Semaphore; } Timeout void Task (void) { Task Initialization; while (1) { Wait on Semaphore; Perform work; } } OSSemPost() OSSemPend() silabs.com | @silabs
- 18. RTOS Services – Signaling Task(s) Using Event Flags § Event Flags are a grouping of bits used to signal the occurrence of more than one events § Signals from ISRs or Tasks § Only tasks can wait for events Task Event Flag Group Set/Clear Flag(s) Timeout void Task (void) { Task Initialization; while (1) { Wait on Event Flag Group; Perform work; } } Task Timeout Wait for ‘ANY’ of the desired flags Wait for ‘ALL’ of the desired flags ISR Set/Clear Flag(s) void TaskEventISR (void) { Clear interrupt; Signal Event Flag Group; } Task ‘N’ Flag(s) ‘M’ Flag(s) OSFlagPend() OSFlagPend() OSFlagPost() OSFlagPost() silabs.com | @silabs
- 19. RTOS Services – Sending Messages to Task(s) § Messages can be sent from an ISR or a task to other task(s) § Messages are typically pointers to data § The data sent depends on the application § The data must remain in scope until no longer referenced Task Task Task Send void ReceiverTask (void) { Task initialization; while (1) { Wait for Message; Process data; } } Receive Producers void SenderTask (void) { Task initialization; while (1) { Produce data; Send to task; } } ISR Timeout OSQPost() OSQPend() Data Send Send Consumer(s) silabs.com | @silabs
- 20. Debugging RTOS-Based Systems – µC/Probe, Graphical Live Watch® § Seeing inside an embedded system § Non-intrusive § Display or change ANY values numerically or graphically § A universal tool that interfaces to any target: § 8-, 16-, 32-, 64-bit and DSPs § No CPU intervention with Cortex-M § Requires target resident code if not using the debug port: § RS232C § TCP/IP § USB § For bare metal or RTOS-Based applications § Micrium’s RTOS and TCP/IP awareness Your Code RTOS (Optional) Libraries Compiler Assembler Linker Debugger Cortex-M Target .ELF IDE µC/Probe .ELF CDF (I/Os) CSF (Custom Symbols) On-the-Fly Memory & I/O Access silabs.com | @silabs
- 21. Debugging RTOS-Based Systems – µC/Probe, Graphical Live Watch® § RTOS awareness § Task state stack usage § CPU usage § Run counters § Interrupt disable time § Kernel objects § Etc. § Built-in 8 channel oscilloscope § Display live data in Microsoft Excel § Scripting § Joystick Interface § Multimedia support § Etc. Micrium’s µC/ProbeTM silabs.com | @silabs
- 22. Debugging RTOS-Based Systems – Segger’s SystemView § Displays the execution profile of RTOS- based systems § Displayed live § Trigger on any task or ISR § Visualizing the execution profile of an application § Helps confirm the expected behavior of your system § Measures CPU usage on a per-task basis § Min/Max/Avg task run time § Counts the number of task executions § Display the occurrence of ‘events’ in your code § Traces can be saved for post-analysis or record keeping silabs.com | @silabs
- 23. Do You Need an RTOS? § Do you have some real-time requirements? § Do you have independent tasks? § User interface, control loops, communications, etc. § Do you have tasks that could starve other tasks? § e.g. updating a graphics display, receiving an Ethernet frame, encryption, etc. § Do you have multiple programmers working on different portions of your project? § Is portability and reuse important? § Does your product need additional middleware components? § TCP/IP stack, USB stack, GUI, File System, Bluetooth, etc. § Do you have enough RAM to support multiple tasks? § Flash memory is rarely a concern because most embedded systems have more Flash than RAM § Are you using a 32-bit CPU? § You should consider using an RTOS silabs.com | @silabs
- 24. § Silicon Labs Integrated Development Environment (FREE): § https://www.silabs.com/products/development-tools/software/simplicity-studio § Silicon Labs Development Boards: § https://www.silabs.com/products/development-tools/mcu § Silicon Labs / Micrium OS Kernel (FREE when using Silicon Labs chips): § https://www.silabs.com/products/development-tools/software/micrium-os § Micrium’s µC/Probe, Graphical Live Watch® (FREE Educational Version): § https://www.micrium.com/ucprobe/trial/ § Segger’s SystemView (FREE Evaluation Version): § https://www.segger.com/downloads/free-utilities/ § Micrium Books (FREE PDF downloads): § https://www.micrium.com/books/ucosiii/ Development Tools and Books silabs.com | @silabs
- 25. S I L A B S . C O M Thank you!