IN2305-II Embedded Programming

Transcription

1 IN2305-II Embedded Programming prof.dr.ir. Arjan J.C. van Gemund Embedded Software Lab Software Technology Dept.

2 Arjan van Gemund? BS Physics Engineering MS, PhD Computer Science DSM (Embedded Systems HW + SW) TNO (High-Performance Computing) TUD (EE, Computer Architecture) TUD (CS, Software Technology, 0.4 fte Prof Emb SW) 2 kids, dog, cat, living in Ravenswoud (Fr) in2305-ii: L1 2

3 In2305-ii? Info: via in2305-ii: L1 3

4 Embedded Systems? ES = computer system (HW+SW) embedded within another system largely determining its functionality printer user I/F netw I/F printing system in2305-ii: L1 4

5 Telegraph network Telegraph printer out-of-order data negotiate with multiple clients (print jobs) service status requests adapt to different printers response time to certain requests data throughput / buffering in2305-ii: L1 5

6 Underground Tank Monitoring System level CH level H 2 O temperature Emb Sys tank 1... tank N buttons LCD disp printer guard levels, detect leaks extremely low-cost design (proc) simple arithmetic - CPU hog - response time problem in2305-ii: L1 6

7 Cruise Control System (Lab Project) Emb Sys speedo meter gas pedal buttons SSD stabilize car speed when engaged extremely low processor cycle budget small control loop jitter due to other activities reliable operation in2305-ii: L1 7

8 Embedded Systems Boom provides functionality (intelligence) of almost everything annual growth 25-60% (Emb Linux > 60%) 100 x PC market accounts for 25-40% costs in automotive very large societal dependence very high performance demands in2305-ii: L1 8

9 Embedded Software Crisis functionality migrates from HW to SW existing cores combined with FPGA s, rather than ASICs programming-centered design (incl. HDLs) TV, mobile, car, MLOC code, expon. growth! despite SW engineering: 1 10 bug / KLOC 100 G$ / yr on bugs (Mars Polar Lander, Mars Climate Orbiter, Ariane 5, Patriot, USS Yorktown, Therac-25,... ) in2305-ii: L1 9

10 Embedded Programming more difficult than classical programming interaction with hardware real-time issues (timing) concurrency (multiple threads, scheduling, deadlock) need to understand underlying RTOS principles event-driven programming (interrupts) lots of (novice) errors (hence the crisis) so that s why we have this course already in 2 nd year in2305-ii: L1 10

11 Example naïve automatic door task (thread): for (;;) { while (inp(sensor)!= 1) ; // wait to open out(door,open); while (inp(sensor) == 0) ; // wait to close sleep(1000); out(door,close); // close after timeout } what are the (many) issues? (discussed on the next slides) in2305-ii: L1 11

12 Specification: FSM (Moore) s 0 s s 1 s s s 2 0: door, timer_enable 1: door, timer_enable 2: door, timer_enable s = sensor, t = timeout t.s e tmr t red transition absent in example code -> door can slam into your face! clk in2305-ii: L1 12

13 How to Program? VHDL: FSM in entity door_controller pros: separate hardware: no problems sharing a processor with other tasks (scheduling, priorities) fast and synchronous programming model: high frequency clocked process with simple polling for s and t cons: VHDL to cumbersome / prohibitive for large applications lots of legacy code written in, e.g., C in2305-ii: L1 13

14 A VHDL Solution process -- fsm begin wait until rising_edge(clk); case state is when S0 => if (s = 1 ) then state <= S1; when S1 => if (s = 0 ) then state <= S2; when S2 => if (s = 1 ) then red arc in FSM state <= S1; if (t = 1 and s = 0 ) then state <= S0; end case; door <= 1 when (state!= S0) else 0 ; timer_enable <= 1 when (state = S2) else 0 ; end process; in2305-ii: L1 14

15 What if C? C: FSM in a task door_controller pros: simple (sequential) programming model cons: can t be invoked periodically by a high-frequency clock (timer) because of polling overhead busy waiting (polling) is not an option (see above) -> concurrent (event) programming (e.g., using interrupts and semaphores) so the while loops in the example code are wrong only use a delay which is not based on busy wait ergo: interrupt programming, using an RTOS in2305-ii: L1 15

16 A C Solution void isr_sensor(void) // process sensor IRQ { OS_Post(semaphore_event_on_s); // signal s changed } void task_door_controller(void) { for (;;) { OS_Pend(semaphore_event_on_s); // wait for s = 1 out(door,open); do { OS_Pend(semaphore_event_on_s); // wait for s = 0 OS_Delay(1000); } while (inp(sensor)!= 0); // timeout out(door,close); } } in2305-ii: L1 16

17 Issues efficient, no busy waiting any more (OS_Pend, OS_Delay) still, code is not correct: interrupts (entering/leaving persons within delay period are not properly handled, and are only accumulated in semaphore (wrong) cannot afford to just sit in a delay, need control flow flexibility of a real FSM, i.e., to jump, AND.. the ability to simultaneously wait for two events (s or t): void isr_sensor_and_timer(void) { // handle both IRQs OS_Post(s_or_t); // either s or t changed } in2305-ii: L1 17

18 Alternative C Solution void task_door_controller(void) { for (;;) { switch (state) { STDBY: OS_Pend(s_or_t); // wait for 0-1 out(door,open); state = OPEN; OPEN: OS_Pend(s_or_t); // wait for 1-0 timer_enable(); state = TIMING; TIMING: OS_Pend(s_or_t); // wait for 0-1 or t if (inp(sensor) == 0) { // timeout out(door,close); timer_disable(); state = STDBY; } else state = OPEN; }}} in2305-ii: L1 18

19 Conclusion Embedded programming is not so easy Nor in C nor VHDL C: Concurrency needed (seq. prog. model): RTOS support Event programming needed: interrupts + RTOS support Learn the basics of interrupt programming and using an RTOS (in C) Learning is (lots of) programming! Lab: simple Cruise Control subsystem Hardware: FPGA board with 32 bit soft core + C tools In2305 via: in2305-ii: L1 19

20 Lab Assignment: Cruise Control engage button: engage cruise control inc button: increment throttle or cruising speed dec button: decrement throttle or cruising speed speed and throttle on SSD monitor link to PC terminal (status, logging,..) engage inc/dec throttle controller vehicle speed in2305-ii: L1 20

21 Cruise Control Setup (throttle) PC host (Linux) Embed. Syst. (FPGA board) m a b (speed) encoder DC motor (vehicle) in2305-ii: L1 21

22 ES Setup engage throttle inc dec PWM m setpoint 32 controller speed 32 decoder a b count m a b in2305-ii: L1 22

23 Demo Demo.. in2305-ii: L1 23

24 Finally.. Grade = f (MC exam, Quiz, Lab) Without lab NO grade Lab: presence mandatory, AWOL -> no grade! Lab enrollment: TA ASAP In2305-ii first time edition! Accept glitches.. Response group (3 student volunteers via ) In2305 via: Credits: Mark Dufour, Sijmen Woutersen in2305-ii: L1 24