Poster WEPMN037
Contents
1. Figure 3 Typical hardware specs e Preemptive priority based soft real time multitasking kernel e Hardware memory protection e UNIX compatible API fcntl stdio sockets pipes semaphores signals etc e Multiple TCP and UDP network connections including login shells e UNIX like shell commands e Simple Remote File System e Concurrently writable system log continuously backed up to remote file server e EPICS code for auto discovery configuration and custom Records e Extensive diagnostics includes remote monitoring and updating of boot images e View plot of system variables in real time e Base functionality available to all applications includes o Read Write from to digital and analog I O signals o Bench and field level calibrations for analog inputs and outputs o Hardware specific initialization during startup o Persistent variables saved to flash BBRAM restored on startup Figure 4 DEBROS software features Is DEBROS right for your project If your project requires sub millisecond response times and use of every last CPU cycle then DEBROS may not be a good fit But if you want a ready to use programming and runtime environment based on UNIX standards then DEBROS could be just what you need Acknowledgments Thanks to Andrew S Tanenbaum and Linus Torvolds for concrete examples of what can be done if you put your mind to it Thanks to Vasu Vuppula NSCL for urging me to publish my wo2. DEBROS A UNIX like OS for 8 bit microcontrollers MICHIGAN STATE UMA a Y Mark A Davis Control Systems Software Group National Superconducting Cyclotron Laboratory introduction Preemptive multitasking simplifies Can low end 8 bit microcontrollers based on decades old technology help run an advanced experimental science facility Yes With the right tools these low end processors can support the basic functionality programmers expect from any UNIX like operating system making them a practical choice for many uses Motivation The lack of a standard software platform for such 8 bit microcontrollers is an impediment to their use in projects they are otherwise well suited for Proprietary tools and programming interfaces require longer learning curves and result in non portable software and increased costs At the National Superconducting Cyclotron Laboratory these and other limitations brought development to a standstill and forced a search for alternatives With no ready made solution available decided to develop one myself Use of a preemptive multitasking kernel eliminates the need for each task to manage its CPU usage and save and restore its own state between task switches int preemptiveTask1l Cint argc char argv printfC Do initialization for 35 printfC Do part 1 while C part2Done printfC Do a little more of part 2 return 0 Fi
3. gure 2 Things are so much simpler when using preemptive multitasking High end features on low end hardware Cooperative multitasking doesn t scale Originally our controllers used the cooperative multitasking mode which works well when tasks are few and short But inevitably the number and capabilities of the tasks grew To maintain acceptable response times was forced to break each task into smaller and smaller pieces each responsible for managing its own CPU usage and saving restoring the task state between calls Tasks became larger more complex less efficient and required more work to maintain int cooperativeTaskl Cunsigned long maxMS Static int state 0 unsigned long startTime switch state case 0 printfC Do initialization State 1 break case lL printfC Do part 1 State 2 break case 2 startTime getmMS while msSince startTime lt maxMS if Cpart2Done state 1 break printfC Do a little more of part2 break default printf State machine error return 1 5 return 0 J Figure 1 Even simple tasks become complex when using cooperative multitasking First installed in 2006 DEBROS now runs on over 150 controllers at the NSCL and its use continues to expand e Rabbit 3000 running at 44 MHz e 768K RAM 200 265K unused e 512K Flash used for basic filesystem e 100BASE T Ethernet
4. rk And thanks to my wife Deborah for her patience while soent hours at home learning and working on DEBROS References DEBROS Developer and User Manual Mark A Davis Controls Software Group NSCL http groups nscl msu edu controls
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