RTAI. Antonio Barbalace (modified by M.Moro 2011) RTAI

Transcription

1 Antonio Barbalace (modified by M.Moro 2011) Real Time Application Interface by Dipartimento di Ingegneria Aereospaziale dell Università di Milano (DIAPM)

2 It is not a complete RTOS It makes Linux kernel fully pre-emptable Some (limited) changes must be applied to the kernel, i.e. interrupt handling and scheduling policies acts essentially as an interrupt dispatcher consider Linux as a background task Antonio Barbalace 2008 RTOS - course 3 User space RT processes RT processes System calls standard processes standard processes Antonio Barbalace 2008 RTOS - course 4

3 History and evolution (1/2): At first it was PCDOS-DIAPM-RTOS (16bits real mode); Then it was implemented in 32 bits real/protected mode; Approaching Linux (2.0.25); NMT-RTL appears and goes on DIAPM-RTL variant was born RTHAL- patch for 2.2.xx kernel ready (beginning 1999) Antonio Barbalace 2008 RTOS - course 5 History and evolution (2/2): April 1999 first version of for UP and SMP; Jan 2001 NMT-RTL now RTLinux was patented; Jun 2002 ADEOS was firstly released; ADEOS substitutes RTHAL and from now on no patent problems; LXRT scheduler was introduced; More than one branch of ; October 2005 Fusion branch becomes a standalone distribution Xenomai; Antonio Barbalace 2008 RTOS - course 6

4 RTHAL To encapsulate all the data structures and time critical functions of the kernel in one defined structure All the original operations work through RTHAL pointers RTHAL pointers are dynamically modifiable can be selectively activated/disactivated Successively substituted by (a modified version of) ADEOS Antonio Barbalace 2008 RTOS - course 7 ADEOS Adaptive Domain Environment for Operating Systems

5 ADEOS Dual-kernel approach Nano kernel Open source NEW NAME: ADEOS/ipipe CHANGES: Functions name Various improvements Antonio Barbalace 2008 RTOS - course 9 ADEOS Linux RTOS ADEOS/ ipipe Dual Kernel with ADEOS/ipipe nano kernel Antonio Barbalace 2008 RTOS - course 10

6 ADEOS co-dos era OS era OS User Process 1 User Process 2 User Process 3 User Process 1 User Process 2 User Process 3 OS Many different OS (or multiple instances of the same OS) running on the same machine, sharing the same hardware. User Process 1 User Process 2 User Process 1 User Process 2 User Process 3 User Process 1 User Process 2 ADEOS era OS 1 OS 2 OS 3 ADEOS/ ipipe Antonio Barbalace 2008 RTOS - course 11 ADEOS Basics: Domains Pipeline Interrupts Events Antonio Barbalace 2008 RTOS - course 12

7 ADEOS - Resource virtualization layer available as a Linux kernel patch/module - It enables multiple domains to share hardware resources - A domain is generally a complete OS but no assumption is made by Adeos on the sophistication of a domain - Domains compete for processing external events (interrupts) or internal ones (traps) - It exports a generic, CPU-independent API to client domains Antonio Barbalace 2008 RTOS - course 13 ADEOS OS domain 1 OS domain 2 C D A ADEOS B A 4 ADEOS communication methods A general usage of the hardware made by a domain B Adeos receives control from the hardware (through HW o SW interrupts) C Two-ways communication (the domain is aware of the presence of Adeos) D Invoking of an OS s interrupt handler (the domain could not be aware of the presence od Adeos) Antonio Barbalace 2008 RTOS - course 14

8 ADEOS event pipeline - A domain can ask ADEOS to be notified of: - Every incoming external interrupt or auto-generated virtual interrupt - Every system call issued by applications - Other system events triggered by the kernel code (task switching, signal notification, task exit, etc.) - Events are dispatched by ADEOS in orderly manner assigning a static priority to each domain - Active domains are orderly queued into a pipeline Antonio Barbalace 2008 RTOS - course 15 ADEOS Interrupt OS domain 1 wired? OS domain 2 OS domain 3 Root domain Linux OS domain n OS domain idle ADEOS/ipipe interrupts/events pipeline (on interrupt) Antonio Barbalace 2008 RTOS - course 16

9 ADEOS Interrupts PROPERTIES: Asynchronous Raised in Maskable (a domain could be stalled) Propagated down the pipeline Logged (Optimistic interrupt protection scheme) A domain can temporarily stall its stage in the pipeline In this state an incoming interrupt is not delivered to the domain s handler, is logged, and is not flowed down to the lowest priority domains Antonio Barbalace 2008 RTOS - course 17 Events ADEOS PROPERTIES: Synchronous Raised mostly for software cause Non maskable Propagated from the source domain up the pipeline Immediate dispatching Antonio Barbalace 2008 RTOS - course 18

10 ADEOS References: Karim Yagmour et others (OperSys Inc) Antonio Barbalace 2008 RTOS - course 19 /ADEOS - is installed as domain with the maximum (relative) priority, higher than the Linux domain serves interrupts before Linux RT processes Linux kernel Standard processes Antonio Barbalace 2008 RTOS - course 20

11 VS Xenomai Linux Linux Xenomai ADEOS/ ipipe asm low-level Linux ADEOS/ ipipe asm low-level Linux immediate dispatching Xenomai pipeline (no immediate dispatching) Antonio Barbalace 2008 RTOS - course 21 VS Xenomai Xenomai Currently ported on: ARM I386, ia64 (SMP, MUP) PowerPC Run: Kernel User Main goal : Fast dispatching API interface: Posix b RTDM Currently ported on: ARM i386, ia64 (SMP) PowerPC, PowerPC64 (SMP) Blackfin Run: Kernel User Main goal : Portability API interface: Xenomai native Posix b VxWorks psos+ VRTX uitron RTDM Antonio Barbalace 2008 RTOS - course 22

12 From our tests: VS Xenomai LESS INTEGRATION PROBLEMS: Xenomai BETTER PERFORMANCE: (immediate dispatching) EASY APPLICATION PORTING: Xenomai DEBUGGING SUPPORT: Both CLEAR, AND WELL ORGANIZED SOURCE CODE: Xenomai Antonio Barbalace 2008 RTOS - course 23 Immediate dispatching

13 Scheduler IPC Basics: ADEOS/RTHAL Scheduler IPC ADEOS/ RTHAL Antonio Barbalace 2008 RTOS - course 25 ADEOS/RTHAL PROVIDES: Immediate Interrupts dispatching Interrupt registering/deregistering functions PIC management routines Timers (8254/APIC) management routines registering/deregistering timers handler functions Trap handlers registering/deregistering functions Provides rt_printk/rt_synch_printk Syscall dispatching Antonio Barbalace 2008 RTOS - course 26

14 8254 Native timer; it supports at least two modes that are used: Periodic Mode Oneshot Mode This timer is used in: UP SMP Counter 0 shared with Linux. APIC At first used with multiprocessor hardware only. Same modes: Periodic Mode Oneshot Mode Used in: SMP MUP ADEOS/RTHAL timers Antonio Barbalace 2008 RTOS - course 27 Timer update Timer update timer_handler{... } timer_handler{... } timer_handler{... } timer_handler{... } timer_handler{... } timer_handler{... } timer_handler{... } timer_handler{... } Periodic Mode Automatic timer register reload Oneshot Mode Compulsory timer register update Antonio Barbalace 2008 RTOS - course 28

15 Scheduler PROVIDES: Task creation/destruction routine Task suspend/yield/sleep routine Task Timer related function Scheduling disciplines/policy LXRT Linux (user space) Real-Time capability Task interface with IPC mechanisms Antonio Barbalace 2008 RTOS - course 29 Scheduler Scheduling policy: RMS EDF FIFO, default scheduler RR Antonio Barbalace 2008 RTOS - course 30

16 Scheduler Scheduling point: on timer interrupt on ISR exit on task self-suspending Self-suspending examples: Yield Suspend Sleep Antonio Barbalace 2008 RTOS - course 31 Scheduler LXRT Scheduler kernel Scheduler user Antonio Barbalace 2008 RTOS - course 32

17 IPCs PROVIDES: Bits (a sort of signals) Fifo Message Mailbox Message queue NetRPC (now requires RTNet) Semaphore Shared memory Antonio Barbalace 2008 RTOS - course 33 References: Paolo Mantegazza, DIAPM Xenomai References: Antonio Barbalace 2008 RTOS - course 34