CMSIS-RTOS An API interface standard for Real-Time Operating Systems

Transcription

1 CMSIS-RTOS An API interface standard for Real-Time Operating Systems Mahanth Gouda Technical Specialist ARM Ltd Skype: gouda.mahanth 1

2 What is CMSIS? ARM Cortex Microcontroller Software Interface Standard Vendor-independent hardware abstraction layer for the Cortex-M processor series Enables consistent and simple software interfaces to the processor and its peripherals Simplifies software re-use, reduces the learning curve for new MCU developers 2

3 CMSIS Components CMSIS-CORE: Standard API for all ARM Cortex -M Processors Standardized software interface for Cortex-M0, Cortex-M3, Cortex-M4 and future processors CMSIS-DSP: DSP Library Collection with 61 Functions Optimized for Cortex-M4, but also available for Cortex-M0, and Cortex-M3 CMSIS-RTOS: Standard API for Real-Time OS Vendors Enables Software Templates, Middleware, Libraries, etc. CMSIS-SVD: System View Description for Peripherals Peripheral Awareness for Debuggers and Header file generation CMSIS-DAP: Standard Debug Interface for all Cortex Processors Access to all registers of the ARM CoreSight Debug Access Port 3

4 MCU CMSIS USER CMSIS Structure Application Code CMSIS-DSP DSP-Library CMSIS-RTOS API Debugger (3 rd Party) CMSIS-CORE Real Time Kernel (3 rd Party) Device Peripheral Functions (Silicon Vendor) SIMD Cortex-M4 Core Peripheral Functions Peripheral Register & Interrupt Vector Definitions CMSIS SVD CMSIS DAP Cortex CPU SysTick RTOS Kernel Timer NVIC Nested Vectored Interrupt Controller Debug + Trace Other Peripherals CoreSight 4

5 CMSIS-RTOS API: Motivation Provide a standardized API for software components Stimulate standard middleware development Enable standard project templates from silicon vendors Simplify usage of CMSIS-DSP Library Simplify programming of Cortex-M processor-based devices Provide SiPs and middleware industry with standard RTOS APIs Reduce learning curve for programmers API designed with the vision for: MPU access protection and multi-processor systems Software eco system that allows application sharing 5

6 Issues with Proprietary RTOS No common API for available RTOS Requires multiple adaptations of middleware and project templates Software architects may try to avoid using an RTOS Kernel if it makes software components more complex Device developers need to learn new RTOS APIs Proprietary RTOS Kernels are frequently generic Do not use Cortex-M Architecture features like LDEX/STEX Proprietary RTOS Kernels can have complex licensing Is it possible to re-distribute example projects? Free might impose some restrictions on usage 6

7 CMSIS-RTOS: Minimum Requirements Preemptive context switching with multiple priorities Mutex, Semaphore, Event signal, and Time management Message queue and Mail queue that works with interrupts Optional features that allow differentiation: Generic Wait function; i.e. with support of time intervals Support of MPU Zero-copy mail queue to support multi-processor systems Deterministic context switching; round-robin context switching Dead lock avoidance i.e. with priority inversion No interrupt disable on Cortex-M3/M4 Usage of Cortex-M3/M4 instructions (i.e. LDEX, STEX) Suitable for all Cortex-M processor variants; 7

8 CMSIS-RTOS: API Structure API Design Considerations Suitable for all Cortex-M Processors Small memory foot print Scalable functionality Prepared for MPU support Prepared for multi-processor systems Application Code main thread interrupt Object definition via macros CMSIS-RTOS API Objects Real Time Kernel (3 rd Party) Function call translation Object Definition With type information that allows type checking and debug views Abstracted via macros to allow efficient call translation 8

9 CMSIS-RTOS: Definition Definition description defines: thread State Changes function, initial priority, stack size ID created at thread starts; multiple thread instances possible ID refer an active thread Pre-emptive context switching with seven easy to understand priorities: Idle, Low, BelowNormal, Normal, AboveNormal, High, Realtime 9

10 CMSIS-RTOS: Management Management Create: start a thread Terminate: stop a thread GetPriority: obtain current thread priority SetPrioirty: change priority of thread ID specifies any active thread ID = NULL allows to refer the current running thread State Changes 10

11 CMSIS-RTOS: Mutex & Semaphore Resource Sharing Mutex: for thread only - for classic thread synchronization Semaphore: for thread - counting semaphore - manages index for direct resource access - semaphores can be also released in ISR Mutex: Synchronization Semaphore: Shared Access wait release wait release Mutex shared resource Semaphore #0 #1 #2 #3 #4 #5 shared resource wait release 11

12 CMSIS-RTOS: Message & Mail I Message/Mail Queues Buffered information exchange between threads or interrupt service routines (ISR) Queue operations: - put info to queue (, ISR) - get info from queue (, ISR) - wait for info ( only) Suited for multi-processor architectures Memory blocks used for mail might be access protected via MPU Message: Integer or Pointer or ISR put Message Queue int / pointer values Mail: Memory Blocks or ISR put Mail Queue memory blocks get get or ISR or ISR 12

13 CMSIS-RTOS: Message & Mail II Message/Mail Description Contain data type for run-time type checking and kernel aware debugging Define queue size and optionally the receiving thread Message: Integer or Pointer or ISR put Message Queue int / pointer values Mail: Memory Blocks or ISR put Mail Queue get get or ISR or ISR memory blocks 13

14 RTX Reference Implementation First implementation of CMSIS-RTOS API based on Keil RTX Available free of charge BSD 3-clause license Short and concise license Allows commercial and proprietary use Compiles with ARM Compiler, GCC and IAR 14

15 Source: EE Times Group Embedded Market Study CMSIS-API: RTOS Potential Operating Systems (kernels) for deeply embedded All have similar basic features But no common API (Cortex-M processorbased MCU) 15

16 CMSIS-RTOS: Making it a Success CMSIS has already created a large community Cortex-M Processors are an Industry Standard MCU Platform Simplifies creation of new devices and tool support CMSIS-RTOS API will extend this to more complex software API specification defined and agreed with CMSIS community A strong statement to drive standardization in the industry Allow superset products with more functionality (MPU support, certification suites, etc.) CMSIS-RTOS Reference Implementation based on Keil RTX Free BSD license including source code: allows flexible usage & distribution 16

17 Thank You 17