IN2305-II Embedded Programming

IN2305-IIEmbedded Programming

prof.dr.ir. Arjan J.C. van Gemund

Embedded Software LabSoftware Technology Dept.

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Arjan van Gemund?

BS Physics EngineeringMS, 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)http://www.st.ewi.tudelft.nl/~gemund/

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In2305-ii?

Info: via http://www.st.ewi.tudelft.nl/~gemund/

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Embedded Systems?

ES = computer system (HW+SW) embedded within another system largely determining its functionality

printingsystem

user I/F

printer

netw I/F

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Telegraph

out-of-order datanegotiate with multiple clients (print jobs)service status requestsadapt to different printersresponse time to certain requestsdata throughput / buffering

Telegraphnetwork printer

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Underground Tank Monitoring System

guard levels, detect leaksextremely low-cost design (proc)simple arithmetic - CPU hog - response time problem

tank 1 tank N

Emb Sys

buttons LCDdisp

printer. . .

level CHlevel H2Otemperature

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Cruise Control System (Lab Project)

stabilize car speed when engagedextremely low processor cycle budgetsmall control loop jitter due to other activitiesreliable operation

speedometer

gas pedal

Emb Sys

buttons SSD

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Embedded Systems Boom

provides functionality (intelligence) of almost everythingannual growth 25-60% (Emb Linux > 60%)100 x PC marketaccounts for 25-40% costs in automotivevery large societal dependencevery high performance demands

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Embedded Software Crisisfunctionality migrates from HW to SWexisting cores combined with FPGA’s, rather than ASICsprogramming-centered design (incl. HDLs)TV, mobile, car, .. 10+ MLOC code, expon. growth!despite SW engineering: 1 – 10 bug / KLOC100 G$ / yr on bugs (Mars Polar Lander, Mars Climate Orbiter, Ariane 5, Patriot, USS Yorktown, Therac-25, ... )

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Embedded Programming

more difficult than “classical” programming interaction with hardware real-time issues (timing)concurrency (multiple threads, scheduling, deadlock)need to understand underlying RTOS principlesevent-driven programming (interrupts)

lots of (novice) errors (hence the crisis)so that’s why we have this course already in 2nd year

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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)

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Specification: FSM (Moore)

0: door’, timer_enable’1: door, timer_enable’2: door, timer_enable

s = sensor, t = timeout

s’

10

s

2

ss’

s

s’

t.s’

red transition absent in example code-> door can slam into your face!

tmre t

clk

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How to Program?

VHDL: FSM in entity door_controllerpros:

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

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A VHDL Solutionprocess -- fsmbegin 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;

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What if C?

C: FSM in a task door_controllerpros:

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 wrongonly use a delay which is not based on busy waitergo: interrupt programming, using an RTOS

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A C Solutionvoid 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); }}

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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}

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Alternative C Solutionvoid 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;}}}

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ConclusionEmbedded programming is not so easyNor in C nor VHDLC:

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 subsystemHardware: FPGA board with 32 bit soft core + C tools

In2305 via: http://www.st.ewi.tudelft.nl/~gemund/

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Lab Assignment: Cruise Controlhttp://auto.howstuffworks.com/cruise-control.htmengage button: engage cruise controlinc button: increment throttle or cruising speeddec button: decrement throttle or cruising speedspeed and throttle on SSDmonitor link to PC terminal (status, logging, ..)

throttle

speed

vehiclecontroller

inc/dec

engage

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Cruise Control Setup

m

(speed)

(vehicle)

Embed. Syst.

(FPGA board)

ab

(throttle)

PC host(Linux)

encoder

DC motor

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ES Setup

controller

inc

engage

dec 32

32

PWM

decoder

m

a

b

setpoint

speed

count

throttle

32

32

m

ab

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Demo

Demo ..

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Finally ..

Grade = f (MC exam, Quiz, Lab)Without lab NO gradeLab: presence mandatory, AWOL -> no grade!Lab enrollment: email TA ASAP

In2305-ii first time edition! Accept glitches ..Response group (3 student volunteers – via email)

In2305 via: http://www.st.ewi.tudelft.nl/~gemund/

Credits: Mark Dufour, Sijmen Woutersen