Interesting Lecture - Embedded Systems

Today

Advanced embedded systems The point of the course Hardware stuff Software stuff

Ariane 5 Details

What happened? Need to look into the flight software…

“Horizontal bias” converted from 64-bit float to a 16-bit integer Software reused from Ariane 4 – a slower vehicle

The 16-bit int overflowed, throwing an exception Uncaught exception shut down the guidance

computer …and the backup computer

Rocket became unguided Started to disintegrate due to aerodynamic forces Then destructed

Mars Pathfinder Lands on Mars July 4 1997 Mission is successful

Behind the scenes… Sporadic total system resets on the rover Debugged on the ground, fixed by software patch

Pathfinder Details

Software run on vxWorks – a multitasking RTOS Vehicle control running at high priority Lots of stuff running at medium priority Meteorological science running at low priority

Problem:1. Low priority software grabs a thread lock

2. High priority software blocks on the lock

3. Medium priority software runs for a long time

4. Total reboot triggered by watchdog timer

This is priority inversion Solutions exist, but you have to know when and

how to use them

CS 7962 Lab 3

ARM7 boards 16364 total bytes of RAM 1024 bytes available for main stack 128 bytes available for interrupt stack

Students used iprintf() call for debugging Prints a string to serial port Uses up to about 2 KB of stack memory

Most groups called iprintf() from both the main context and interrupt context

Result Unpredictable operation due to memory

corruption Software crashes

Stack Problems

The students Knew about stack overflow problems Knew the stack requirements of iprintf() And still made the mistake

The Point #1

Easy: Hack up some embedded software that seems to work

Hard: Make a rocket take off, fly to Mars, land a rover,

drive it around, report back to Earth 1 bug == total mission failure

Write control software that’s going to run on 25 M hybrid vehicles 1 bug == product recall (at best)

Make a pacemaker that operates correctly for 10 years in every person using one 1 bug == lost lives, product recall, irreparable

damage to company reputation

The Point #2 Embedded system isn’t just a collection of

isolated parts Many design decisions have implications

for the whole system – are we using: Threads? Interrupts? Heap allocation? Address spaces?

Many important system properties are global Stack and heap memory usage Effects of failures and bugs Energy usage Real-time deadlines

The Point #3

Making a good embedded system isn’t just hacking

All of these are just as important: Understanding the requirements Understanding the application domain Platform choice Toolchain choice Software architecture Timing analysis Memory usage analysis Fault vulnerability analysis Testing Certification

The Point #4

Reading the reference manual is easy PWM, ADC, DAC, SCI, SPI, UART, I2C, CAN, LIN,

802.15.4, …

Seeing the big picture is hard Main goal of my class: Help you see the

bigger picture

Lab Hardware

Philips LPC 2129 Serial port for programming JTAG port for debugging

Philips LPC2xxx

Basic idea: Philips licenses the ARM7TDMI-S core from ARM, adds lots of cool external stuff, manufactures the chips

LPC21xx 64 pins LQFP64 package – 1cm x 1cm No external bus

LPC22xx 144 pins LQFP144 package – 2cm x 2cm External bus

LPC2129

Cost: $6.75 in large quantities Designed for automotive and control

applications Memory

16 KB on-chip SRAM 256 KB on-chip flash This has to suffice since there’s no external bus!

2 CAN channels CAN == Controller Area Network LAN for control applications Primarily used in automobiles Why 2 channels?

More LPC2129

4 10-bit ADC channels A/D: Convert voltage in 0-3v range into a 10-bit

integer A/D is slow – typically interrupt on completion

4 external interrupt lines Lots of general-purpose I/O lines

Shared with other functionality

I2C and SPI Standard embedded serial busses Generally used in master-slave mode Of course, serial protocols can also be

implemented through bit-banging

More LPC2129

2 UARTs Point-to-point serial communication Lots of convenient features to reduce CPU usage

FIFOs Buffer overrun detection Interrupts

2 timers 32-bit timers with 32-bit prescalers Lots of features!

Real-time clock Keeps calendar time

More LPC2129 PWM

Pulse width modulation Sort of a cheapo D/A converter

Rapidly switch between low and high voltage, rely on external circuitry to average out

Watchdog timer Reboot wedged processor

PLL – phase locked loop Converts external 10-25 MHz clock into 10-60

MHz internal clock

MAM – memory accelerator module Prefetches instructions Exploits multiple banks of flash memory Solves the problem of core outrunning the flash

More LPC2129

JTAG support Provide visibility and controllability into the

processor – used for debugging and testing

Power management Idle mode

Processor core shuts down until interrupt or reset arrives

Peripherals keep running Power down mode

RAM and registers saved Peripherals shut down Extremely low power consumption

ARM Stuff

32-bit RISC Designed to be a compiler target

Lots of registers Conditional execution Most instructions can use barrel shifter

Multiple processor modes We use ARM7TDMI

Bottom end of the ARM family No caches or memory protection hardware Runs below 100 MHz

High end ARMs are pretty fast ~1 GHz

Example: GCD

int gcd (int i, int j)

{

while (i != j) {

if (i>j) {

i -= j;

} else {

j -= i;

}

}

return i;

}

GCD in ARM Assembly

000000d4 <gcd>:

d4: e1510000 cmp r1, r0

d8: 012fff1e bxeq lr

dc: e1510000 cmp r1, r0

e0: b0610000 rsblt r0, r1, r0

e4: a0601001 rsbge r1, r0, r1

e8: e1510000 cmp r1, r0

ec: 1afffffa bne dc <gcd+0x8>

f0: e12fff1e bx lr

Labs

1. Get started with the board

2. Data acquisition – angle measurement

3. Analysis and measurement of stack depth and interrupt latency

4. Audio input using ADC

5. Audio output using PWM

6. Audio DSP

7. CAN bus networking

8. Feedback control

9. Distributed control

That’s All

Class is supposed to be fun Offered Fall 2006 Talk to current students I hope you’ll take it