1. CprE 458/558: Real-Time Systems (G. Manimaran)1 RTLinux Lab – Introduction Cpre 558 Anil anil@iastate.edu

2. CprE 458/558: Real-Time Systems (G. Manimaran)2 Contents Real-Time Operating System (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

3. CprE 458/558: Real-Time Systems (G. Manimaran)3 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

4. CprE 458/558: Real-Time Systems (G. Manimaran)4 Can Linux provide real-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

5. CprE 458/558: Real-Time Systems (G. Manimaran)5 Can Linux provide real-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

6. CprE 458/558: Real-Time Systems (G. Manimaran)6 Commercial RTOS RTLinux – Monolithic kernel with loadable modules QNX – Microkernel approach VxWorks – Monolithic kernel LynxOS – Microkernel ARTS, Spring, KURT, RTAI, etc….

7. CprE 458/558: Real-Time Systems (G. Manimaran)7 Open source Linux 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

8. CprE 458/558: Real-Time Systems (G. Manimaran)8 Linux Kernel System libraries Device drivers Linux kernel Hardware I/OHardware Interrupts User Processes

9. CprE 458/558: Real-Time Systems (G. Manimaran)9 RTLinux Kernel Hardware System libraries Device drivers Linux kernel I/O Software Interrupts User Processes RTLinux Plug-in Real Time Tasks RT-Scheduler I/OHardware Interrupts Linux is executed in the background Direct h/w access

10. CprE 458/558: Real-Time Systems (G. Manimaran)10 Linux Kernel: code perspective Linux Monolithic kernel core M1 M2 M3 M4 Kernel Loadable Modules RAM DISK Module M2 service (system call) User Process M2 THE controller

11. CprE 458/558: Real-Time Systems (G. Manimaran)11 RTLinux Kernel: code perspective Linux Monolithic kernel core RTM2 RTM3 M1 M2 Kernel Loadable Modules RAM DISK Load RT core RT Load command RT-Core Module RT core M3 THE controller

12. CprE 458/558: Real-Time Systems (G. Manimaran)12 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/lin ux-2.4.29.tar.gz 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

13. CprE 458/558: Real-Time Systems (G. Manimaran)13 So, How do we 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!!!!

14. CprE 458/558: Real-Time Systems (G. Manimaran)14 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.

15. CprE 458/558: Real-Time Systems (G. Manimaran)15 Lab Policies Six assignments 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

16. CprE 458/558: Real-Time Systems (G. Manimaran)16 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

17. CprE 458/558: Real-Time Systems (G. Manimaran)17 Handling the hard disk (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

18. CprE 458/558: Real-Time Systems (G. Manimaran)18 Handling the hard disk (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

19. CprE 458/558: Real-Time Systems (G. Manimaran)19 RTLinux Lab# 1 Cpre 558 Anil anil@iastate.edu

20. CprE 458/558: Real-Time Systems (G. Manimaran)20 Lab 1: Objectives Part 1: –Getting the RTLinux lab setup ready Part 2: –Run a few simple hello-world modules

21. CprE 458/558: Real-Time Systems (G. Manimaran)21 Part 1 Install the 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

22. CprE 458/558: Real-Time Systems (G. Manimaran)22 Part 2 Boot into 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)

23. CprE 458/558: Real-Time Systems (G. Manimaran)23 A kernel module Vs. 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

24. CprE 458/558: Real-Time Systems (G. Manimaran)24 A typical kernel module Init_module() { ……. Perform your module initiation stuff etc.. } Cleanup_module() { ……. Perform cleanup stuff like destroying the threads, freeing memory, etc.. }

25. CprE 458/558: Real-Time Systems (G. Manimaran)25 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

26. CprE 458/558: Real-Time Systems (G. Manimaran)26 A typical RTLinux module 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

27. CprE 458/558: Real-Time Systems (G. Manimaran)27 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

28. CprE 458/558: Real-Time Systems (G. Manimaran)28 RTL_PRINTF: how does it work? Rtl_printf printk Printk buffer Kernel ring buffer syslodg console Might overflow!! Log file

29. CprE 458/558: Real-Time Systems (G. Manimaran)29 Other ways of printing: 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

30. CprE 458/558: Real-Time Systems (G. Manimaran)30 RTL-FIFO Creating and destroying 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

31. CprE 458/558: Real-Time Systems (G. Manimaran)31 Using RTL_FIFO RT Task: my_put task Linux Task: my_read task RTL FIFO rtf_create() Time rtf_put() open() read() rtf_destroy()

32. CprE 458/558: Real-Time Systems (G. Manimaran)32 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.

33. CprE 458/558: Real-Time Systems (G. Manimaran)33 Thank You!!