Important Note: EE Herald has now (from October
2012) published embedded systems design practice using latest
kits from ST Microelectronics and NXP Semiconductors based
on the popular ARM Cortex M0 processor core. The old AME
51 kit for which the sample program explained from next
paragraph in this module is not avaialable in the market
now. We strongly recommend not to use AME 51 kit, instead
read our module3b
based on ARM Cortex M0 powered ST MIcro's Disocvery kit
and and module3a
based on ARM Cortex M0 powered NXP LPCXpresso kit to get
into practical learning of embedded systems programming.
Sample program for ST kit is available at esmod4bsample
and esmod6b
and sample program for NXP kit is available at esmod4asample
and esmod6a.
MODULE -4: Sample
Program for old AME 51 kit from OKI
OK - Let us start now with "real" hardware (board)
and real "software".
One thing you should make sure is that you have the hardware
board and the necessary software installed on your PC.(if
at all you have purchased the OKI development board) and
read about the various documents available with that.
Reading of Module-3 is good enough to install h/w and
s/w. However if you need further details, search for AME-51
lite on www.okisemi.com
for user manual docs of this kit. Click
on this link to dowload the same from our website.
First thing you need to have is an "editor".
Basically editor is a program by which we can "see"
and "alter" source codes. There are plenty of
editors available from normal notepad to highly sophisticated
editors, which would be part of IDE (Integrated Development
Environment). To start with let us start using an editor
called "Notepad ++". This is freeware (no need
to pay any money for this). You can download this from
following link. In case if you can not find this freeware,
the ordinary notepad of any windows operating system can
be used.
http://sourceforge.net/project/showfiles.php?group_id=95717&package_id=102072
Once you have installed the development environment provided
by OKI - you would have "ame51gnu" directory
(folder) in C:\ drive. You can browse through various
folders in this "C:\ ame51gnu\" and get to know
how the source code is organized for examples etc.
674051 Directory
There are at least 4 sub directories within 674051 Directory.
Below figure explains the meaning of each of this item.
Common Directory holds two more subfolders (i) INC and
(ii) SRC.
INC folder holds all the header files for source programs.
SRC holds the common assembler and C programs.
They would be locate at "C:\ame51gnu\Examples\674051\COMMON\INC"
and "C:\ame51gnu\Examples\674051\COMMON\SRC"
respectively.
The contents of these folders would be shown as below.
Project Directory (example Hello)
This "Hello" directory is taken as an example
folder (as most of you would be aware of "Hello world"
program in the beginning of your C language learning days).
This folder (as well others also) consists of "hello.c"
(this would be different for other example programs),
"flash.ld" and "Makefile" - this would
be same (at least the name of these files) in all other
example programs also.
Hello.c : This is the main source program.
Flash.ld : Linker script which defines how the program
places into RAM and ROM of the chip
Makefile : It defines the compiler and linker setting.
It automates the whole compiling process by just typing
"gnumake"
With this background of understanding file structure,
how they are organized, and how the typical source code
directory would look like (like hello directory), let
us start embed ourselves in to our first embedded program.
You should know how an output device is connected (and
what is the output device used), intricacies of this output
device etc… So let us start our first program with
LED. Let us turn ON an LED. Here are the basic steps to
be followed.
1) First copy the LED directory as TestLED. Now you would
have TestLED folder as well in "C:\ame51gnu\Examples\674051"
directory
2) Rename the LED.c in this directory as TestLED.c (you
can use dos command "ren" or press "F2"
in windows to rename).
3) Open the TestLED.c file with "Notepad++"
and delete all the content.
4) Insert the following code in this file (TestLED.c)
int main(void)
{
int i;
volatile unsigned char * ModeRegister;
volatile unsigned char * OutputRegister;
ModeRegister = 0xB7A04008;
OutputRegister = 0xB7A04000;
*ModeRegister = 0x01; // Configure Port E bit 0 as outuput
while (1)
{
*OutputRegister = 0x01; // Set the Port E bit 0 as 1
//Delay
for (i=0; i<1000000; i++)
;
*OutputRegister = 0x00; // Set the Port E bit 0 as 0
//Delay
for (i=0; i<1000000; i++)
;
}
}
5) Open the "Makefile" (in the same directory)
and replace the line number 12 as OUT
= TestLED . Basically
this command tells the compiler
to name the outfile as TestLED.hex
6) Now compile the code -
To compile, open the DOS
prompt of your system (to open the dos prompt click on
the start button/icon of your
window OS and look for run in the menu list and
click on it. Type "cmd" or "command"
in the entry space and click
ok). Now the DOS prompt will open to a default location.
Now type the DOS command
"cd \ame51gnu\examples\674051\TestLED\"
at the DOS prompt.
Type "gnumake"
at the DOS prompt to compile. Now the program should compile
(any error! read the
embedded_kit_manual.pdf.
for detailed program compiling and running guidance).
7) After compiling check in the folder \ame51gnu\examples\674051\TestLED\,
you could see a new file called TestLED.hex
is created. This stores the hexadecibal machine langauge
code of this program.
8) Load this TestLED.hex file into the board through serial
port connected from PC to board using Tera term pro software
already loaded on your PC. To learn how to load the program
read embedded_kit_manual.pdf.
9) After loading the program change the switch positions
from stand alone mode to SRAM mode and press the reset
button.
10)Now you would see the RED LED blinking. It will turn
ON and OFF - continuously.
Here is the explanation of the code.
1) Generally any processor or microcontroller would have
some ports. These are called General Purpose Input Output
(GPIO).
Here you may ask - why these are called GPIO or Ports?
If you recall - in earlier days any "goods"
that should enter or leave a country would be transported
through ships and these ships would be entering or leaving
ports of that country. In the same way if you want to
send any signal you should put the signal in the port
and it would be send. Conversely, if you wish to receive
any signal - you should receive (or read) using the ports.
2) The ARM Chipset used in this board has Port 0 to Port
15. Each port has different bit width(some ports has 8
bits, some have 7, some have 6 and some are with only
5, which could be used for any purpose (so called as GPIO).
3) In this example we are using Port E - bit (0). Each
port can contain any number of individual bits that can
be used (generally port would have 8 bits). This is like
saying 8 ships can arrive or depart from this port. Always
note that these bits (or anything in embedded world) would
be counted from 0! So 8 bits means bit 0 to bit 7 are
available.
4) In a way - we are forced to use this Port E - bit(
0), because this is the bit, which is connected to RED
LED in our kit. So it is always required for embedded
engineers/ programmers to have the complete understanding
of the hardware - how it is connected like? what is connected
to? where it is connected ?and why. Read the manual embedded_kit_hw_manual.pdf
to know how the LEDs are connected.
5) Now we know that, we need to make this Port E - bit
(0) high (called some times logical 1 - or simply the
voltage becomes +5V) to make the LED to glow and Port
E - bit (0) to Low (called some times logical 0 - or simply
the voltage becomes 0V) to turn off the LED.
6) You cannot use a port to write and read just like that!
You need to tell the processor (in our case ARM chipset)
that we are using the particular port and particular bit
as output or input. This is like having two-way line -
we need to "go" out in left and "come"
in back in right. ARM chipset provides a "Mode control"
register, which does this job.
7) So in summary - we need to "tell" the processor
that we are using Port E - bit (0) as output and make
this bit high and low in a continuous loop.
8) Now look at the code once again.
I. "int i"
is used as general purpose variable (used for delay).
II. ModeRegister and OutputRegister
are used as 8 bit pointers (both have 8 - GPIOs)
III. ModeRegister is at 0xB7A04008
and OutputRegister is at 0xB7A04000 (Note any ports would
have address
- This address is used to access particular port)
IV. Now configure this Port e
- bit 0 as out put by writing 0x01 (as last bit is made
1).
V. Now write 0x01 to OutputRegister
to glow the LED and write 0x00 to turn off the LED.
VI. Do this in a loop so that
LED turns ON and OFF continuously.
Click on the text below to enter Module-5
Next
Module - 5(ARM-7 processor architecture)
Previous
Module - 3(Installation of the kit)
ABOUT THIS COURSE:
Totally EEHerald plan to bring 12 modules. You can
be assured of completing basic course in Embedded Systems
after studying and practicing exercises in all the modules.
We will give priority to programming and serial communications
(SPI, USB, CAN etc..) part. To receive a copy of total
course syllabus, please email to us.
This free tutorials on embedded systems is prepared
by embedded professionals with more than10 years of industrial
experience, however we want your feedback on this course
content; please email your questions, suggestions and
comments to editor@eeherald.com. Your questions on present
modules will be answered in the revised modules. We may
change the course content based on the majority of your
requests and feedbacks.
Please let your friends know about this course, we request
you to email this link to your friends and colleagues
who are interested in embedded system.
