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Rt linux-lab1
- 1. J.SUDARSHANREDDY RTLinux Lab –Introduction Cpre 558 J.SUDARSHANREDDY 01/25/15
- 2. J.SUDARSHANREDDY Contents • Real-Time OperatingSystem (RTOS) Vs. General Purpose OS (GPOS) • Can Linux provide real-time guarantees? • Commercial RTOSs • RTLinux Vs. Linux: Architectural comparison • RTLinux Vs. Linux: Code perspective • Get the RTLinux setup ready • Things to Issue and Handling the hard disk • Lab #1: Detailed discussion 01/25/15
- 3. J.SUDARSHANREDDY RTOS Vs. GPOS •RTOS – needs deterministic timing behavior – Works under worst case assumptions • GPOS – high throughput and fairness – Optimizes for the average case • Hence, the design objectives of the OSs are different 01/25/15
- 4. J.SUDARSHANREDDY Can Linux providereal-time guarantees? -- No!! • Linux – non-preemptible kernel • A system call might take long time to complete – Coarse timer resolution • Tasks can be released only with 10ms precision – Virtual memory • Introduces unpredictable amount of delays – Variable priority • Each task is assigned a priority which varies over the time; this is to achieve fairness 01/25/15
- 5. J.SUDARSHANREDDY Can Linux providereal-time guarantees? -- No!! (contd..) • Linux – Linux will batch several operations for efficient use of H/W delaying all tasks – Linux also reorders requests from multiple processes for H/W efficiency – Linux does not preempt low priority task in a system call, instead queues the high priority task – Linux makes high priority tasks to wait for low priority tasks to release resources Therefore, Linux cannot provide real-time guarantees 01/25/15
- 6. J.SUDARSHANREDDY Commercial RTOS • RTLinux– Monolithic kernel with loadable modules • QNX – Microkernel approach • VxWorks – Monolithic kernel • LynxOS – Microkernel • ARTS, Spring, KURT, RTAI, etc…. 01/25/15
- 7. J.SUDARSHANREDDY • Open sourceLinux project • Supports x86, PowerPC, Alpha • Available as a patch to the regular Linux kernel • Provides an RT API for developers • Runs Linux kernel as lowest priority process RTLinux: Overview 01/25/15
- 8. J.SUDARSHANREDDY Linux Kernel System libraries Devicedrivers Linux kernel Hardware I/O Hardware Interrupts User Processes 01/25/15
- 9. J.SUDARSHANREDDY RTLinux Kernel Hardware System libraries Devicedrivers Linux kernel I/O Software Interrupts User Processes RTLinux Plug-in Real Time Tasks RT-Scheduler I/O Hardware Interrupts Linux is executed in the background Direct h/w access 01/25/15
- 10. J.SUDARSHANREDDY Linux Kernel: codeperspective Linux Monolithic kernel core M1 M2 M3 M4 KernelLoadableModules RAM DISK Module M2 service (system call) User Process M2 THE controller 01/25/15
- 11. J.SUDARSHANREDDY RTLinux Kernel: codeperspective Linux Monolithic kernel core RTM2 RTM3 M1 M2 KernelLoadableModules RAM DISK Load RT core RT Load command RT-Core Module RT core M3 THE controller 01/25/15
- 12. J.SUDARSHANREDDY Getting RTLinux ready •Configure and compile a fresh Linux kernel (2.4.29) – Download the kernel from http://www.kernel.org/pub/linux/kernel/v2.4/linux-2.4 • Patch the RTLinux to the Linux kernel • Recompile the kernel and reboot the system into the new kernel • Configure the RTLinux kernel and compile it 01/25/15
- 13. J.SUDARSHANREDDY So, How dowe run a RT-application program ? • Step 1: Write the RT-application program as a kernel module – (You are still in Linux) • Step 2: Compile the module and check for errors – (You are still in Linux) • Step 3: Load the RT-Core (or RT Scheduler, etc..) and the RT-application program module – (After this we will be in RTLinux) • Step 4: Now you are in RTLinux!!!! 01/25/15
- 14. J.SUDARSHANREDDY Homework • Submission 1: –Give a ten line write-up comparing RTLinux with Linux with at least five differences along with the references. • Submission 2: – Give a ten line write-up comparing RTLinux with two other commercial RTOSs with at least five differences for each of them along with the references. 01/25/15
- 15. J.SUDARSHANREDDY Lab Policies • Sixassignments in total • First three assignments are mandatory • One of the last three assignments is mandatory • You will be working with a removable hard disk which can be issued from CSG 01/25/15
- 16. J.SUDARSHANREDDY Things to Issue •Issue the following from the CSG – Hard disk (one per group) – Key (one per group) – RHEL – WS3 installation DVD (one per group) • You need to download the lab01 tar file (lab01.tgz) from the course website. • The RTLinux lab is in Coover - 1331C 01/25/15
- 17. J.SUDARSHANREDDY Handling the harddisk (1) • Shutdown the PC • After the power is off, unlock the existing hard disk and take it out • Insert the hard disk given to you and lock it • Restart the comp • Follow the manual you have downloaded from the course website 01/25/15
- 18. J.SUDARSHANREDDY Handling the harddisk (2) • After you are done with the lab: – Shutdown the PC – After the power is off, unlock the hard disk and remove it – Insert the original hard disk and lock it – Leave the Lab 01/25/15
- 19. J.SUDARSHANREDDY Lab 1: Objectives •Part 1: – Getting the RTLinux lab setup ready • Part 2: – Run a few simple hello-world modules 01/25/15
- 20. J.SUDARSHANREDDY Part 1 • Installthe RHEL-WS3 using the DVD given to you – Go for the auto-partitioning option – Rest everything is straightforward • Configure and compile fresh Linux kernel (2.4.29) • Patch the RTLinux to the Linux kernel • Recompile the kernel and reboot the system into the new kernel • Load RT-modules • Instructions are provided in the Lab manual 01/25/15
- 21. J.SUDARSHANREDDY Part 2 • Bootinto the RTLinux kernel compiled in part-1 • The objectives of the part 2 are: – Understanding a simple RTLinux kernel module • With one thread (hello-1) and two threads (hello-2) – Printing from a RTLinux module • rtl_printf (hello-3) • Using rtf_put (RT-FIFO) (hello-4) 01/25/15
- 22. J.SUDARSHANREDDY A kernel moduleVs. Program • All RT-Tasks are kernel modules. Therefore, we write kernel modules in this lab. • A user program runs in user space and the kernel module runs in the kernel space • A user program starts running at its “main” function • A kernel module starts running at the “init_module” function and exits via “cleanup_module” function • Therefore, for a kernel module “init_module” and ‘cleanup_module” are as necessary as “main” is necessary for a C program 01/25/15
- 23. J.SUDARSHANREDDY A typical kernelmodule Init_module() { ……. Perform your module initiation stuff etc.. } Cleanup_module() { ……. Perform cleanup stuff like destroying the threads, freeing memory, etc.. } 01/25/15
- 24. J.SUDARSHANREDDY Hello world Module •Go through the hello world module • Realize the importance of init_module and cleanup_module • Notice the way the thread is created and how it is made periodic • Understand the “pthread_make_periodic” and “pthread_wait” and other interfacing functions 01/25/15
- 25. J.SUDARSHANREDDY A typical RTLinuxmodule Init_module() { For each thread: Choose the priority function //pthread_set_priority(..); Assign the “task_function” to the thread Create the thread //pthread_create(.., task_function,..); } Task_function() { Pthread_make_periodic_np( p); while(1) { Pthread_wait_np(); //perform the task function //for this instance } } Cleanup_module() { ……. Delete the thread //pthread_delete_np(..); } This function tells the scheduler that I am a periodic task with period “p” This function tells the scheduler that I am done for this instance and schedule me after “p” units of time 01/25/15
- 26. J.SUDARSHANREDDY Hello World 2 •This module creates two threads using a nice “thread_struct” structure to make the initialization easy and compact. • Once again go through the interfacing funcitons • This time put more “rtl_printf” statements and open “/var/log/messages” file to find your output 01/25/15
- 27. J.SUDARSHANREDDY RTL_PRINTF: how doesit work? Rtl_printf printk Printk buffer Kernel ring buffer syslodgconsole Might overflow!! Might overflow!! Log file 01/25/15
- 28. J.SUDARSHANREDDY Other ways ofprinting: RTL-FIFO • RTLinux FIFO provides communication mechanisms between RTL threads and Linux task. • A linux process creates the RTL-FIFO buffer which the RTL threads access and write and read from them 01/25/15
- 29. J.SUDARSHANREDDY RTL-FIFO • Creating anddestroying FIFOS: – Using functions: rtf_create and rtf_destroy – These functions are called from linux process: open(), read(), write(); • Accessing FIFOs from RTL threads – using functions: rtf_put and rtf_get 01/25/15
- 30. J.SUDARSHANREDDY Using RTL_FIFO RT Task: my_puttask Linux Task: my_read task RTL FIFO rtf_create() Time rtf_put() open() read() rtf_destroy() 01/25/15
- 31. J.SUDARSHANREDDY Submissions • Submission 1: –Submit a five line write-up explaining the working of the two RTL interfacing functions including: • Pthread_make_periodic_np • Pthread_wait_np • Rtf_create,rtf_destroy, rtf_put, rtf_get • Submission 2: – Submit a five line write-up giving at least five differences between a kernel module and a user program. 01/25/15
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