UBC104
Embedded Systems
Review: Introduction to Microcontrollers
Processors

General purpose
processors:






80386
Pentium
Core Duo
Large number of pins
External memory
External peripherals
* Figure from Intel 386 DX Datasheet
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General Purpose Registers

Registers are dedicated for
moving data




EAX, EBX, ECX, EDX: general
purpose registers
EBP: Base pointer
ESP: Stack pointer
ESI, EDI: Index register
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Microcontrollers



Support for peripherals inside uController
Limited number of pins
Dedicated purpose


Controlling devices, taking measurements
Controller families:




68H12: Motorola 68H11, 68HC12, …
8051: Intel 8051, 8052, 80251,…
PIC:
Microchip PIC16F628, 18F452, 16F877, …
AVR: Atmel ATmega128, ATtiny28L, AT90S8515,…
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Rita51J

8051

128K of SRAM
128K FLASH ROM



Serial port
Digital I/O lines
* Figure from www.rigelcorp.com
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Motes

Sensor nodes based on Atmel ATMega128
* Figures from CrossbowMPR-MIBUser Manual
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Microcontroller Families




68H12: Motorola 68H11, 68HC12, …
8051: Intel 8051, 8052, 80251,…
PIC:
Microchip PIC16F628, 18F452, 16F877, …
AVR: Atmel ATmega128, ATtiny28L, AT90S8515,…
 We are going to look at 8051s
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Typical 8051s


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32 input / output lines.
Internal data (RAM) memory - 256 bytes.
Up to 64 kbytes of ROM memory (usually flash)
Three 16-bit timers / counters
9 interrupts (2 external) with two priority levels.
Low-power Idle- and Power-down modes
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Datasheets – Your New Friends!
* Figure from Atmel AT89C51RD2 Datasheet
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Pin-Out of an 8051
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8051 Components


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Ports
RAM
Interrupt Controller
Timer
SPI Controller
* Figure from Atmel AT89C51RD2 Datasheet
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8051 Internal RAM & SFRs
* Figure from Atmel AT89C51RD2 Datasheet
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Special Function Registers (SFR)
* Figure from Atmel AT89C51RD2 Datasheet
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Special Function Registers (SFR)
* Figure from Atmel AT89C51RD2 Datasheet
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* Figure from Atmel AT89C51RD2 Datasheet
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Ports

Driving low-power peripherals ie. LEDs, relays
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Accessing Ports in C
void main (void) {
unsigned int i;
unsigned char j;
/* Delay var */
/* LED var */
while (1) {
for (j=0x01; j< 0x80; j<<=1) {
P1 = j;
for (i = 0; i < 10000; i++) {
wait ();
}
}
for (j=0x80; j> 0x01; j>>=1) {
P1 = j;
for (i = 0; i < 10000; i++) {
wait ();
}
}
/* Loop forever */
/* Blink LED 0, 1, 2, 3, 4, 5, 6 */
/* Output to LED Port */
/* Delay for 10000 Counts */
/* call wait function */
/* Blink LED 6, 5, 4, 3, 2, 1 */
/* Output to LED Port */
/* Delay for 10000 Counts */
/* call wait function */
}
}
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Summary

General information about 8051

Special Function Registers (SFRs)


Control of functionality of uController
Ports

Input/Output of uController
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UBC104
Embedded Systems
Motivation for Next Topics
Tasks for Microcontroller

Controlling of processes (autonomic)


e.g. speed of vehicles, chemical processes
Control of devices through human operator

e.g. remote control, etc
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Example: Controller Engineering
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Topics for the Following Lectures
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
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Interrupts & Timers
Communication
Analog to digital (A/D) conversation
Pulse Width Modulation
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UBC104
Embedded Systems
Interrupts & Timers
Today’s Topics


Interrupts
Timers
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Interrupts
Definition of ‘Interrupt’
Event that disrupts the normal execution of a
program and causes the execution of special
instructions
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Interrupts
Program
time t
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Interrupts
Interrupt
Program
time t
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Interrupts
Interrupt
Program
Program
Interrupt Service Routine
time t
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Interrupt Handling

Address space in
code space
Code that deals with interrupts:
Interrupt Handler or Interrupt
Service Routines (ISRs)
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Interrupt Handling

Code that deals with interrupts:
Interrupt Handler or Interrupt
Service Routines (ISRs)

Possible code:
Interrupt number
void ISR(void) interrupt 1 {
++interruptcnt;
}
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Interrupts
fahr= (cent *
9
) +32
5
Interrupt
Program
mov R1, cent mul R1, 9 div R1, 5 add R1, 32
mov fahr, R1
time t
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Interrupts
Interrupt
Program
Program
mov R1, cent
mul R1, 9
Interrupt Service Routine
mov R1, 0x90
mov sensor, R1 ret
time t
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Interrupts
Interrupt
Program
mov R1, cent
Program
Save
Context
Interrupt
Service
Routine
Restore
Context
mul R1, 9
time t
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Interrupts
Interrupt
Program
mov R1, cent
Program
Save
Context
eg push R1
Interrupt
Service
Routine
Restore
Context
mul R1, 9
eg pop R1
time t
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Interrupt Overheads
Interrupt arrives
Complete current instruction
Save essential register information
Vector to ISR
Save additional register information
Interrupt
Latency
Execute body of ISR
Restore other register information
Return from interrupt and restore essential
registers
Resume task
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Interrupt
Termination
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Interrupt Response Time
Interrupt Latency
Interrupt Response Time= Interrupt Latency + Time in Interrupt Routine
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Interrupts

Internal or External
Handling can be enabled/disabled
Prioritized

General 8051:





3x timer interrupts,
2x external interrupts
1x serial port interrupt
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Interrupt Priorities

Each interrupt source has an
inherent priority associated
with it
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Interrupt Priorities


Priorities can be adapted
by programs
Original 8051 provides 1bit per interrupt to set the
priority
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2-bit Interrupt Priorities

The 89C52RD2 provides 2bit-interrupt priorities
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2-bit Interrupt Priorities (continued)
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2-bit Interrupt Priorities (continued)
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External Interrupts
Pins for
external interrupts
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External Interrupts

External Interrupts:
Level- or edge-triggered
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External Interrupts

External Interrupts:
Level- or edge-triggered
Level-triggered
threshold
trigger point
t
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External Interrupts

External Interrupts:
Level- or edge-triggered
Level-triggered
threshold
t
trigger point
Edge-triggered
trigger point
t
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Timer

A timer is a counter that is
increased with every time an
instruction is executed e.g.
8051 with 12MHz increases
a counter every 1.000 µs

General 8051 has 3 timer:
 2 16-bit timer
 1 16-bit timer with extrafunctionality (introduced
with the 8052)
Timer/Counter Mode Control Register TMOD
Timer/Counter Control Register TCON
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Timer High- & Low-Registers
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SFR Map – Timer Registers
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Timer Control
Timer/Counter Mode Control Register TMOD
Timer/Counter Control Register TCON
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SFR Map – Timer Control
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SFR Map – Timer 2
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Timer Code
void TimerInit(void) {
// Timer 2 is configured as a 16-bit timer,
// which is automatically reloaded when it overflows
// This code (generic 8051/52) assumes a 12 MHz system osc.
// The Timer 2 resolution is then 1.000 µs
// Reload value is FC18 (hex) = 64536 (decimal)
// Timer (16-bit) overflows when it reaches 65536 (decimal)
// Thus, with these setting, timer will overflow every 1 ms
T2CON
TH2
RCAP2H
TL2
RCAP2L
=
=
=
=
=
ET2 = 1;
TR2 = 1;
0x04;
0xFC;
0xFC;
0x18;
0x18;
//
//
//
//
//
Load
Load
Load
Load
Load
Timer
Timer
Timer
Timer
Timer
2
2
2
2
2
control register
high byte
reload capt. reg. high byte
low byte
reload capt. reg. low byte
// Enable interrupt
// Start Timer 2 running
}
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Interrupt Code for Timer 2
void handleTimer2 (void) interrupt 5 {
/* execute interrupt code */
}
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Interrupt Flags

Bits that are set if the
interrupt occurs
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Code for Interrupt Flags
/* Configure Timer 0 as a 16-bit timer */
TMOD &= 0xF0;
/* Clear all T0 bits (T1 left unchanged) */
TMOD |= 0x01;
/* Set required T0 bits (T1 left unchanged) */
ET0 = 0;
/* No interrupts */
/* Values for 50 ms delay */
TH0 = 0x3C;
/* Timer 0 initial value (High Byte) */
TL0 = 0xB0;
/* Timer 0 initial value (Low Byte) */
TF0 = 0;
/* Clear overflow flag */
TR0 = 1;
/* Start Timer 0 */
while (TF0 == 0); /* Loop until Timer 0 overflows (TF0 == 1) */
TR0 = 0;
/* Stop Timer 0 */
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Summary: Interrupts

Definition of ‘Interrupt’:
Event that disrupts the normal
execution of a program and causes the
execution of special instructions
Level-triggered
threshold




Handling can be enabled/disabled
Prioritized
Internal or External
External Interrupts:



trigger point
t
Edge-triggered
Level-triggered
Edge-triggered
8051: 3 timer interrupts, 2 external
interrupts & a serial port interrupt
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trigger point
t
57
Real-Time Systems

Definition:
A real-time system needs to be
predictable
in terms of values and time

Correctness of an RT system depends on functionality
as well as temporal behaviour
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Clock Driven Scheduling


Invoke Scheduler
Pick & dispatch a job
Timer Interrupt Service Routime

Decision on what job execute
are made at specific time
instants chosen a priori before
the system starts operation
A schedule of jobs is created
off-line and used at run time
The scheduler dispatches jobs
according to the stored
schedule at each scheduling
decision time
Clock-driven scheduling has
minimal overhead during run
time
Set timer
No interrupt

Start
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Block waiting for timer
interrupt
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Cyclic Executive
#define TASK_MAX 4
typedef void (func_ref)(void);
int delay[TASK_MAX];
func_ref task_ref[TASK_MAX];
void cyclic_executive() {
int task= 0;
while(1) {
settimer(delay[task]);
taskref[task]();
task= (task==TASK_MAX) ? task+1 : 0;
clear(time_flag);
while (time_flag) enterIdleMode();
}
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Cyclic Executive (continued)
void timer(void) interrupt 5 {
set(time_flag);
}
void EnterIdleMode(void) {
PCON |= 0x01;
}
Frame
Tdelay,1
T1
T2
T3
T1
T2
T3
t
IdleMode
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Problems with Cyclic Executives


Timing Accuracy
Actually constructing the cyclic executive
(Typical realistic problem: 40 minor cycles and 400 entries)

Inflexibility



must reconstruct schedule even for minor changes
Incorporating Aperiodic/Sporadic Tasks, or very
long period tasks
I/O only by polling
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General Embedded Programming
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
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Endless loops
Idle mode for 8051
Generic main() function
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Endless Loops

Two types of tasks:


Run-To-Completion tasks
Endless-Loop tasks
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Endless Loops

Two types of tasks:




Run-To-Completion tasks
Endless-Loop tasks
Interrupt handler are run-to-completion tasks
The majority of generic tasks are endless loops
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Endless Loops

Two types of tasks:





Run-To-Completion tasks
Endless-Loop tasks
Interrupt handler are run-to-completion tasks
The majority of generic tasks are endless loops
Example Code:
void ExampleTask(void) {
while(1) {
waitForActivation;
doTask;
}
}
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Idle Mode

8051s implement an “idle” mode
which consumes less power
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Idle Mode

8051s implement an “idle” mode
which consumes less power
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Idle Mode

8051s implement an “idle” mode
which consumes less power

from Pont: Atmel 89S53


normal mode
idle mode
11mA
2mA
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Idle Mode

8051s implement an “idle” mode
which consumes less power

from Pont: Atmel 89S53



normal mode
idle mode
11mA
2mA
Example Code:
void EnterIdleMode(void) {
PCON |= 0x01;
}
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Generic main() Function
void main(void) {
/* initialize system */
/* initialize tasks */
while (1) {
EnterIdleMode();
}
/* loop forever */
/* PCON |= 0x01*/
}
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Summary

Cyclic executives

Endless loops

Idle mode
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