ee 308: microcontrollers - introductionelosery/spring_2018/ee308/lectures/intro.pres.pdf · ee 308:...

EE 308: MicrocontrollersIntroduction

Aly El-Osery

Electrical Engineering DepartmentNew Mexico Institute of Mining and Technology

Socorro, New Mexico, USA

January 6, 2018

Overview Choosing a Microcontroller Microcontroller Architectures AVR Microcontroller Atmega1284 Assembly vs C ToolchainAly El-Osery (NMT) EE 308: Microcontrollers January 6, 2018 1 / 23

What are microcontrollers?

A microcontroller is a processor with memory and severalother components integrated on a a single chip making itperfect for a variety of applications covering a wide range,e.g., coffee machines, automotive industry,communications, defense systems, satellites, etc.


Differences between microcontrollers and microprocessor

Microcontroller

CPU SRAMEEPROM/

FlashTimer/

Counter

Digital I/Omodule

Serialinterface ADC Other

peripherals

Microcontroller

Contains a processorHas memory and I/O modules integrated onthe same chipCompactCheapSmall power consumption

Microprocessor

CPU SRAMEEPROM/

FlashTimer/

Counter

Serialinterface ADC Digital I/O

moduleGeneral PurposeMicroprocessor

Processor is standalone, memory and I/Omodules are seperateDesigner can choose components for memoryand I/OHigh processing powerGeneral purpose


Variety of microcontroller manufacturers

68HC11/12 — Freescale Semiconductors’s (Formerly Motorola)8051 — IntelAVR — AtmelZ8 — ZilogPIC — Microchip


Evaluation boards

BigAVR6

ATtiny85

Dragon12 Plus

Zilog


Embedded systems

Control unit performed by a microcontroller is integrated into the system.


Mechatronics

Integration for mechanical systems with electronics and information processing.


Factors to consider

Capability of meeting the specification of the task at handSpeedPackagingPower consumptionAmount of memoryNumber of I/O pinsUpgradabilityCost

Development toolsAvailability


CISC vs RISC

Complex Instruction Set Computer (CISC)Larger architectureVariable code sizePowerful instruction setRequires several clock cycles to execute instructions

Reduced Instruction Set Computer (RISC)Simple architectureSmall set of instructionsOne or few clock cycles to execute instructions


Von Neumann vs Harvard

Von Neumann

CPU

Codememory

Datamemory

Von Neumann architecture

data bus

address bus

control bus

Code and data are accessed through thesame busResults in a bottle neck since we can’taccess code and data at the same timeMore delays

Harvard

CPUCode

memoryData

memory

address bus

data bus

control bus

address bus

data bus

control bus

Harvard architecture

Separate buses for accessing code anddataFasterLess delaysRequires more hardware


AVR Core

RISC with Harvard architectureCode ROMData RAMData EEPROMTimersI/O portsADCPWMCommunication interfaces: USART, SPI,I2C (TWI), CAN, USB


Atmega1284

RISC architecture131 instructions (most executes insingle clock cycle)128K bytes code ROM4K bytes EEPROM16K bytes SRAMJTAGTimers/counters, PWM, 8-channel10bit ADCWatchdog timerUSART, SPI, I2C


Atmega1284 PDIP Package

This will be the chip usedthrough out the semester.


Reasons for using assembly

More efficient use of computing power and memoryCloser to the hardwareIf mass production is the goal, then there will be money saving by going to smallercheaper parts


Assembly language

Assembly language consists of, instructions referred to as mnemonics, directives andlabels.

.INCLUDE "M1284DEF.INC"LDI R16 , hi8(RAMEND)OUT SPH , R16LDI R16 , lo8(RAMEND)

5 OUT SPL , R16 ;initialize stack pointer

SBI DDRC , 0 ;set bit 0 of DDRCHERE:

SBI PORTC , 010 CALL DELAY ;call DELAY subroutine

CBI PORTC , 0CALL DELAYRJMP HERE

15 DELAY:LDI R20 , 255

DL1: DEC R20BRNE DL1RET


Assembly language

Assembly language consists of, instructions referred to as mnemonics, directives andlabels.

.INCLUDE "M1284DEF.INC"LDI R16 , hi8(RAMEND)OUT SPH , R16LDI R16 , lo8(RAMEND)

5 OUT SPL , R16 ;initialize stack pointer

SBI DDRC , 0 ;set bit 0 of DDRCHERE:

SBI PORTC , 010 CALL DELAY ;call DELAY subroutine

CBI PORTC , 0CALL DELAYRJMP HERE

15 DELAY:LDI R20 , 255

DL1: DEC R20BRNE DL1RET

Directive

Label

Instruction

Comment


Software tools

GNU AVR toolchain (will be used in lectures)FreeOpen sourceLinux and Windows (WinAVR)Arduino IDE is based on itRequires a bit more effort to make it work

Atmel Studio (mostly used in the lab)FreeSupports all their productsRuns only on WindowsHas and additional assembler (used by default): avrasm2Can’t handle mixed C and assembly, and relies on GCC to do that


What to download on the microcontroller

Assembler — replaces mnemonics by their opcodes, resolves include directives,translates register names to addresses, removes comments, etc.avr-as -mmcu=atmega1284 -o ex.o ex.s

Linker — links multiple filesavr-ld -mavr51 -o ex.elf ex.o

Translate object filesavr-objcopy -j .text -j .data -O ihex -o ex.hex ex.elf


Intel Hex vs S19

Intel Hex

:1000000000E40EBF0FEF0DBF389A409A0E940C001B:1000100040980E940C00F9CF4FEF4A95F1F70895F0:00000001FF

Start code (:)Byte count data only (2 characters)Address (4 characters)Record type (2 characters)00 data record01 end of file

Data (2k characters)Checksum (2 characters)

Motorola S19

S01100006578616D706C65345F332E686578C9S113000000E40EBF0FEF0DBF389A409A0E940C0017S113001040980E940C00F9CF4FEF4A95F1F70895ECS9030000FC

Record type (2 characters)S0 Block headerS1-3 Data recordsS5 Record countS7-9 End of block

Byte count (2 characters) Address + Data + ChecksumAddress (4 characters)Data (2k characters)Checksum (2 characters)


Downloading the hex file

avrdude -v -c dragon_jtag -p m1284 -Pusb -U flash:w:ex.hex


avr-as vs avrasm2

There are differences between the GCC assembler and the one used by Atmel. For full listyou need to consult the documentation but below are some of the frequently used ones.

avr-as avrasm2.equ DDRA, 0x01 .equ DDRA = 0x01.asciz “hello” .db “hello”,0.section .data .dseg.section .text .cseghi8 highlo8 low


Programmer

Prototyping areaProgramming Interfaces

SPIHigh Voltage SerialParallelJTAGPDIaWire

Debugging InterfacesJTAGdebugWIREPDIaWire


Makefile

FILENAME = example

MCU = atmega1284PARTNO = m1284ARCH = avr51PORT = usbPROGRAMMER = dragon_jtag

AS = avr-asLD = avr-ldOBJCOPY = avr-objcopyPROG = avrdude

ASFLAGS = -mmcu=$(MCU) --gstabsLDFLAGS = -m$(ARCH)OBJFLAGS = -j .text -j .data -O ihexPRFLAGS = -v -c $(PROGRAMMER) -p $(PARTNO) -P$(PORT)

.PHONY: all install clean

all: $(FILENAME).hex $(FILENAME).o $(FILENAME).elf

%.o: %.s$(AS) $(ASFLAGS) -o $@ $<

%.elf: %.o$(LD) $(LDFLAGS) -o $@ $<

%.hex: %.elf$(OBJCOPY) $(OBJFLAGS) $< $@

install: $(FILENAME).hex$(PROG) $(PRFLAGS) -U flash:w:$<

clean:rm -f $(FILENAME).hex $(FILENAME).elf $(FILENAME).o


Arduino environment

Free packageArduino language implemented in C/C++Lots of librariesA lot of copy/pasteHides a lot of the details and therefore

Makes you lazyOptimization requires extensive redesign of codeResulting code may not operate under strict timing, memory, power requirements

As an engineer, specifically an embedded systems engineer, you must understand enough aboutwhat you are designing, standards and specifications, and have the ability to validate and verifyyour design. The Arduino environment may not give you the ability to do so.

Very useful to non-technical users, hobbyists, students (K-12), but highly questionable forcritical engineering designs


ee 308: microcontrollers - introductionelosery/spring_2018/ee308/lectures/intro.pres.pdf · ee 308:...

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