Today
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Advanced embedded systems
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The point of the course
Hardware stuff
Software stuff
Ariane 5 Details
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What happened? Need to look into the flight
software…
“Horizontal bias” converted from 64-bit float to
a 16-bit integer
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The 16-bit int overflowed, throwing an
exception
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Software reused from Ariane 4 – a slower vehicle
Uncaught exception shut down the guidance
computer
…and the backup computer
Rocket became unguided
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Started to disintegrate due to aerodynamic forces
Then destructed
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Mars Pathfinder
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Lands on Mars July 4 1997
Mission is successful
Behind the scenes…
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Sporadic total system resets on the rover
Debugged on the ground, fixed by software patch
Pathfinder Details
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Software run on vxWorks – a multitasking
RTOS
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Problem:
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2.
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4.
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Vehicle control running at high priority
Lots of stuff running at medium priority
Meteorological science running at low priority
Low priority software grabs a thread lock
High priority software blocks on the lock
Medium priority software runs for a long time
Total reboot triggered by watchdog timer
This is priority inversion
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Solutions exist, but you have to know when and
how to use them
CS 7962 Lab 3
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ARM7 boards
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Students used iprintf() call for debugging
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16364 total bytes of RAM
1024 bytes available for main stack
128 bytes available for interrupt stack
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
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Unpredictable operation due to memory
corruption
Software crashes
Stack Problems
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The students
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Knew about stack overflow problems
Knew the stack requirements of iprintf()
And still made the mistake
The Point #1
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Easy: Hack up some embedded software
that seems to work
Hard:
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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
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Embedded system isn’t just a collection of
isolated parts
Many design decisions have implications
for the whole system – are we using:
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Threads?
Interrupts?
Heap allocation?
Address spaces?
Many important system properties are
global
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Stack and heap memory usage
Effects of failures and bugs
Energy usage
Real-time deadlines
The Point #3
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Making a good embedded system isn’t just
hacking
All of these are just as important:
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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
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Reading the reference manual is easy
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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
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Philips LPC 2129
Serial port for programming
JTAG port for debugging
Philips LPC2xxx
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Basic idea: Philips licenses the ARM7TDMI-S
core from ARM, adds lots of cool external
stuff, manufactures the chips
LPC21xx
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64 pins
LQFP64 package – 1cm x 1cm
No external bus
LPC22xx
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144 pins
LQFP144 package – 2cm x 2cm
External bus
LPC2129
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Cost: $6.75 in large quantities
Designed for automotive and control
applications
Memory
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16 KB on-chip SRAM
256 KB on-chip flash
This has to suffice since there’s no external bus!
2 CAN channels
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CAN == Controller Area Network
LAN for control applications
Primarily used in automobiles
Why 2 channels?
More LPC2129
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4 10-bit ADC channels
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4 external interrupt lines
Lots of general-purpose I/O lines
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A/D: Convert voltage in 0-3v range into a 10-bit
integer
A/D is slow – typically interrupt on completion
Shared with other functionality
I2C and SPI
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Standard embedded serial busses
Generally used in master-slave mode
Of course, serial protocols can also be
implemented through bit-banging
More LPC2129
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2 UARTs
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2 timers
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Point-to-point serial communication
Lots of convenient features to reduce CPU usage
 FIFOs
 Buffer overrun detection
 Interrupts
32-bit timers with 32-bit prescalers
Lots of features!
Real-time clock
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Keeps calendar time
More LPC2129
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PWM
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Watchdog timer
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Reboot wedged processor
PLL – phase locked loop
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Pulse width modulation
Sort of a cheapo D/A converter
 Rapidly switch between low and high voltage,
rely on external circuitry to average out
Converts external 10-25 MHz clock into 10-60
MHz internal clock
MAM – memory accelerator module
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Prefetches instructions
Exploits multiple banks of flash memory
Solves the problem of core outrunning the flash
More LPC2129
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JTAG support
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Provide visibility and controllability into the
processor – used for debugging and testing
Power management
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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
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32-bit RISC
Designed to be a compiler target
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Multiple processor modes
We use ARM7TDMI
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Lots of registers
Conditional execution
Most instructions can use barrel shifter
Bottom end of the ARM family
No caches or memory protection hardware
Runs below 100 MHz
High end ARMs are pretty fast
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~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
d8: 012fff1e
dc: e1510000
e0: b0610000
e4: a0601001
e8: e1510000
ec: 1afffffa
f0: e12fff1e
cmp
bxeq
cmp
rsblt
rsbge
cmp
bne
bx
r1, r0
lr
r1, r0
r0, r1, r0
r1, r0, r1
r1, r0
dc <gcd+0x8>
lr
Labs
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Get started with the board
Data acquisition – angle measurement
Analysis and measurement of stack depth
and interrupt latency
Audio input using ADC
Audio output using PWM
Audio DSP
CAN bus networking
Feedback control
Distributed control
That’s All
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Class is supposed to be fun
Offered Fall 2006
Talk to current students
I hope you’ll take it