Microcontroller basics

Transcription

1 FYS3240 PC-based instrumentation and microcontrollers Microcontroller basics Spring 2011 Lecture #4 Bekkeng

2 Lab: AVR Studio and WinAVR software Microcontrollers can be programmed using Assembly or C language AVR studio Has built-in AVR assembler Has built-in AVR simulator Has built-in STK500 programmer Works as editor for Assembly and C WinAVR (C compiler) includes the GNU GCC compiler for C and C++.

3 Microcontroller (µc or uc) Microcontrollers have: CPU Memory I/O Microcontroller characteristics: Used for control and measurements (not a general-purpose computer) Does one task and runs one program continuously Low power (e.g. 50 mw vs. 50 W or more for a PC) Don t have keyboard and monitor jacks (example of an embedded system) Must use ports to perform I/O Selecting a microcontroller Should be appropriately scaled for the job

4 Microprocessors vs. Microcontrollers

5 CISC vs. RISC CISC (Complex Instruction Set Computer) Many modern microcontrollers are based on the CISC concept. The typical CISC microcontroller has well over 80 instructions, many very powerful and specialised. The advantages of the CISC architecture is that many of the instructions are macro-like, allowing the programmer to use one instruction in place of many. RISC (Reduced Instruction Set Computer) The benefits of RISC design simplicity are a smaller chip, smaller pin count, and very low power consumption.

6 Types of microcontrollers Small microcontrollers 8 bit 20 pins UART Example: ATtiny from Atmel Medium microcontrollers 8/16 bits 44 pins ADCs Example: ATmega from Atmel Large microcontrollers 32 bit 256 pins (BGA) DMA Example: ARM9 Increasing amount of RAM Increasing features

7 Common medium size uc resources Counters UART (Universal Asynchronous Receiver/Transmitter) A/D Converters Time-multiplexing of channels is common Usually 12 or less bits per sample (8, 10, 12 bits common) SPI (Serial Peripheral Interface) I2C (at least slave function)

8 Digital Data Transfer SynchronousTransfer Data sent at constant rate using a shared periodic clock AsynchronousTransfer (i.e., Handshaking) Data sent upon request using handshake signals Tx and Rx still have internal clocks, they just don t share them

9 UART UART = Universal Asynchronous Receiver/Transmitter. A UART is usually an individual integrated circuit used for serial communications over a computer or peripheral device serial port. UARTs are now commonly included in microcontrollers. A dual UART, or DUART, combines two UARTs into a single chip. Many modern ICs now come with a UART that can also communicate synchronously; these devices are called USARTs (universal synchronous/asynchronous receiver/transmitter).

10 Full duplex SPI SPI = Serial Peripheral Interface Serial data link (bus) standard that operates in full duplex mode Devices communicate in master/slave mode where the master (only one master) device initiates the data frame. Multiple slave devices are allowed with individual slave select (chip select) lines. Sometimes SPI is called a "four-wire" serial bus, contrasting with three-, two-, and one-wire serial buses. Serial Clock (output from master) Serial Data In Serial Data Out ncs Bit rate usually in the MHz range Short distance communication Longer cables means lower speed

11 ADCs with SPI interface Many ADCs have an SPI interface Example: MCP Channel,12-Bit A/D Converters with SPI Interface

12 I2C I²C = Inter-Integrated Circuit Is a multi-master serial computer bus (but only one master at a time) Uses only two bidirectional lines Data (SDA) Clock (SCL) Speed up to 3.4 Mbit/s (high speed mode) 100 kbit/s or 400 kbit/s more common? Practical communication distances are limited to a few meters The longer the cable, the lower the speed

13 Network Microcontrollers Some microcontrollers also have built-in Ethernet support

14 Softcore and Hardcore uc in FPGAs Processor cores inside the FPGA Softcore CPU Programmable logic in the FPGA is used to implement a processor (when needed) together with other functionality Hardcore CPU The processor is implemented in the FPGA at the production of the circuit Xilinx processor cores for FPGA Power PC (hardcore processor) MicroBlaze (softcore processor) Altera processor core for FPGA NIOS II (softcore processor)

15 Atmel AVR uc The AVR architecture was conceived by two students at the Norwegian Institute of Technology (NTH) The original AVR uc was developed at a local ASIC house in Trondheim called Nordic VLSI (now Nordic Semiconductor) Different AVR uc series: tinyavr : the ATtiny series (a small uc) megaavr : the ATmega series (a medium uc) XMEGA : the ATxmega series (a medium uc) The names of the uc series gives an indication of the "complexity" (available features) of the device.

16 Example uc: ATmega323 Low-power AVR 8-bit Microcontroller RISC Architecture Most Single-clock Cycle Execution Up to 8 MIPS throughput at 8 MHz Two 8-bit Timer/Counters One 16-bit Timer/Counter Four PWM Channels 8-channel, 10-bit ADC Byte-oriented 2-wire Serial Interface Programmable Serial USART SPI Serial Interface Programmable Watchdog Timer with Separate On-chip Oscillator On-chip Analog Comparator

17 ATmega323

18 AVR ATmega323 (selected) Pin descriptions Port A (PA7..PA0) 8-bit bi-directional I/O port analog inputs to the A/D Converter Port B (PB7..PB0) Port C (PC7..PC0) Port C also serves the functions of the JTAG interface Port D (PD7..PD0) RESET (external reset) INT0 external Interrupt Request 0 (IRQ0) XTAL1 XTAL2 AREF analog reference pin for the A/D Converter

19 IO-ports Direction of the IO-port decided by the content in the DDRn" register. DDRn high gives an output When configured as an output we write to the "PORTn" register. When configured as an input we read from the "PINn" buffer.

20 I/O Port APIs AVR-GCC - Examples

21 Example code I

22 Interrupts Interrupts halt normal code execution in order to go do something more important or time sensitive Used Instead of polling Can be generated internally or externally Interrupts are used e.g. for: RESET Timers Time-Critical Code Hardware signaling such as a switch pressed by the user

23 Interrupt on ATmega Alle avbrudd er i utgangspunktet maskert vekk når mikrokontrolleren starter opp, slik at disse må enables først. I tillegg må globale avbrudd enables i statusregisteret. Inkluderer io.h og interrupt.h for å få tilgang til register- og avbruddshåndtering #include <avr/io.h> #include <avr/interrupt.h> // Enabler avbrudd på external interrupt 0 og 1 falling edge MCUCR = (1<<ISC11) (1<<ISC01); // Avbrudd på fallende flanke GICR = (1<<INT1) (1<<INT0); // Enabler avbrudd på INT1 og INT0 // Enabler globale avbrudd sei(); // Globale avbrudd kan skrues av med kommandoen cli() (lik asm("cli")) while(1); // Vent på avbrudd Tilkoblinger på STK500: SW0 -> PD2 (INT0) SW1 -> PD3 (INT1) LED0 -> PB0 LED1 -> PB1

24 Interrupt API AVR-GCC - Examples See table on next slide for signal names

25 ATmega16 interrupt vectors #define SIG_INTERRUPT0 _VECTOR(1) #define SIG_INTERRUPT1 _VECTOR(2) #define SIG_OUTPUT_COMPARE2 _VECTOR(3) #define SIG_OUTPUT_COMPARE2 _VECTOR(3) #define SIG_OVERFLOW2 _VECTOR(4) #define SIG_INPUT_CAPTURE1 _VECTOR(5) #define SIG_OUTPUT_COMPARE1A _VECTOR(6) #define SIG_OUTPUT_COMPARE1B _VECTOR(7) #define SIG_OVERFLOW1 _VECTOR(8) #define SIG_OVERFLOW0 _VECTOR(9) #define SIG_SPI _VECTOR(10) #define SIG_UART_RECV _VECTOR(11) #define SIG_UART_DATA _VECTOR(12) #define SIG_UART_TRANS _VECTOR(13) #define SIG_ADC _VECTOR(14) #define SIG_EEPROM_READY _VECTOR(15) #define SIG_COMPARATOR _VECTOR(16) #define SIG_2WIRE_SERIAL _VECTOR(17) #define SIG_INTERRUPT2 _VECTOR(18) #define SIG_OUTPUT_COMPARE0 _VECTOR(19) #define SIG_SPM_READY _VECTOR(20)

26 Example code II - Interrupt UDR is the UART s data register

27 STK500 lab kit In-System Programming

28 Alternatives to using microcontrollers For measurement and control applications a PC with a suitable DAQ-card can be a more suitable solution FPGA (FYS4220) DSP (digital signal processor) A specialized microprocessor with an optimized architecture for mathematical operations to be performed quickly (e.g. FFT)

29 C programming Note: in C you can only call functions that have been defined earlier

30 Increment Operators

31 C programming Pointers I &i get the address of the variable i *p get the content of the address location that the pointer points to

32 C programming Pointers II

33 C programming - Memory Management Allocate memory : malloc() Free used memory : free() Look out for memory leakage!

34 More on C-programming See EssentialC.pdf See splan.xml See