Embedded Programming

Alexander Nelson

September 16, 2019

University of Arkansas - Department of Computer Science and Computer Engineering

Programming for Embedded

Differences from desktop programming:

• Input/Output

• Math

• Memory and Hardware

• Code Development

Let’s use the Arduino Uno platform as an example

1

Input/Output

Typical Input/Output on Embedded Devices handled by memory

mapped input/output called “ports”

• Memory Mapped Digital I/O

• Serial Ports

• Analog to Digital Converter (ADC or A/D)

2

Arduino Uno (AtMega328P)

ADC Pins

Digital I/O & PWM

Serial UART

Serial I2C

Serial SPI

Power Pins3

AtMega328P Block Diagram

4

AtMega328P Pinout

5

Em

bedd

ed C

ontr

olle

rs87

6

Core CPU Architecture

• Data & Program Memory

Separated

• Registers are 8-bits

• R26-R31 compose three

16-bit values with

upper/lower bits

7

Arithmetic

8

Arithmetic

No floating point support!

Every arithmetic operation completes in at most 2 cycles

9

AtMega328P Pipeline

AtMega328P has 2-stage pipeline

Fetch, execute

Decoding of instruction occurs during fetch cycle

10

Memory

AtMega328P has separate program(flash) memory and data

(SRAM) memory

11

Persistent Storage

Program Memory is persistent (flash)

Data memory is not (SRAM)

AtMega328P has 1K bytes EEPROM (Electrically Erasable

Programmable Read-Only Memory) for persistent data storage

12