IAR005 Geting Started With the IAR Embedded Workbench

7/28/2019 IAR005 Geting Started With the IAR Embedded Workbench

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IAR Application Note AVR-005, Sep 99

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end

init

Configure

Port B

Configure

Port D

return

pollpb

Read

If PBpressed

debounce

return readpb

debounce time

Scale time to ms

Configure timer

While timer


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Program description - points of interestThe DSDs clearly show the structure of the program and the functions. Each

function has its own DSD. The main function shows a continuous loop after

initial setting up of the variables and low level functions. This will be the

normal feature of most embedded control functions. Loops show up clearly asclockwise lines, with arrows to show the direction. The main function takes

action only if the pushbutton is pressed. Note how a function is called up

from within the if statement -

(if (pollpb==0)), one example of the flexibility of C. The layout of a C

program is very flexible but it is good practice to keep the braces to show start

and end of a code block in line with each other. This makes it easier to check

that you have nested them correctly. Nested loops or decisions should also be

indented to show them up, and so that you can match the source code with the

DSD.

The functions are contrived to show how values can be passed into them,and/or return values from them. This is shown, in the DSD, by the box at the

side of the appropriate terminator box. For instance the function debounce,

takes in a 16-bit value (int) and uses it to feed the 16-bit timer of the AVR

(TCNT1), after scaling to convert it into milliseconds. The function pollpb

takes nothing in (void) but returns the value of the pushbutton, '1' = not

pressed, '0' = pressed.

Hints and Tips

The list below shows some useful tips which could help produce readable,

tighter and more efficient code with ICCA90:

Structure your program using some useful method and use it to dry run theprogram, before coding.

Separate the program into functional blocks.

Tab the source code in several times before you start typing. The editorhas no margin control and this will allow a good print output to be

obtained with margins.

Comment your program as you progress, because you will never go backand do it later! (I have been there!)

Keep to local auto variables wherever possible to allow the compiler to

use and reuse registers instead of SRAM (faster execution and less code). Use char type variables wherever possible to reduce code size.

Use the increment (e.g. x++) or decrement operator (e.g. x--) instead ofx=x+1 or x=x-1 to allow the compiler to use the MCUs efficient INC and

DEC instructions.

Indent code blocks and matching braces to ease readability andmaintenance.

Define constants at the start of the program to make global changes easier

later. e.g. #define DELAY (20)

Use upper case characters for constants to make them show up as

constants. That way you will not try to change them in the program!


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Define the main function as type C_task to stop the compiler preservingand restoring registers on entry and exit, wasting valuable stack space.

The main function will NEVER be exited in an embedded control

program.

Use FLASH ROM for constant storage ( using flash keyword) instead of

SRAM (there is more of it). Accessing flash is more complicated with theAVR because it has a HARVARD architecture, with ROM and RAM

accessed by separate address buses. This is covered by another

application note. (This application example uses the look-up table in

SRAM to take the easy way out!)

:KDW\RXJDLQE\XVLQJ(PEHGGHG&Clearly, the low level adaptations that requires many lines of assembly code,

can be done in C using the IAR C language extensions, thus increasing

readability and portability. The arduous job of initializing the stack, setting

up loops and decision branches, looking up addresses and other timeconsuming tasks, are now done by the compiler/linker. The powerful program

development functions, strong integration with third party tools, and project

management tools make this a very efficient system to use.

&RQFOXVLRQThe combination of IAR Embedded Workbench and the Atmel AVR is a

difficult one to beat in the 8-bit, or even 16-bit field of Embedded

applications. Using C for Embedded application development considerably

speeds up the development and software maintenance process, recouping the

cost of the system usually in one or two projects.

Contact information

USA

IAR Systems Inc.

One Maritime Plaza

San Francisco,

CA 94111

Tel: +1 415-765-5500

Fax: +1 415-765-5503

Email: [email protected]

SWEDEN

IAR Systems AB

P.O. Box 23051

S-750 23 Uppsala

Tel: +46 18 16 78 00

Fax: +46 18 16 78 38


GERMANY

IAR Systems AG

Posthalterring 5

D-855 99 Parsdorf

Tel: +49 89 90 06 90 80

Fax: +49 89 90 06 90 81


UK

IAR Systems Ltd.

9 Spice Court,

Ivory Square

London SW11 3UE

Tel: +44 171 924 3334

Fax: +44 171 924 5341


www.iar.com

Copyright 1999 IAR SystemsIAR and C-SPY is registered trademarks of IAR Systems. IAR Embedded Workbench is a trademark of IAR Systems. Windows is a

trademark of the Microsoft Corporation. All other products are registered trademarks or trademarks of their respective owners.

Product features, availability, pricing and other terms and conditions are subject to change by IAR Systems without prior notice.

IAR005 Geting Started With the IAR Embedded Workbench

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