INTRODUCTION
For this lab you will write a C code subroutine to approximate the square root of an argument using a bisection
method. All the math is done with integers, so the resulting square root will also be an integer. This lab will develop an
appreciation of the steps involved in cross-compiling for, and downloading to, an embedded target board.
HARDWARE
There is no hardware requirement for this lab. We will be simulating a C167 uC in the Keil IDE software.
PROCEDURE
1. Start the Keil µVision 5 Integrated Development Environment (IDE) program.
2. From the top Project drop-down menu, create a new uVision project and save to a new folder (Keil makes a range of
files and sub-folders). Make sure not to have any spaces (underscores are fine) in the project name – this breaks the
linker. Select the legacy device database and the Infineon C167CR-LM target. Click Ok, and then Yes to adding a copy
of ‘START167.A66’.
3. Open the options for target from the top menu bar.
4. Set external memory locations per the image below, then hit Ok.
5. Add new item to source group 1. Select .c file. Name the file main.
6. Complete the ‘main’ function and write a static C function that takes the passed argument and returns the square root.
Some considerations: The ‘sqrt’ function returns a value from 0 to 65535, so you should select an appropriate return
type, as well as argument type. The result variable is declared ‘volatile’ to ensure you can inspect its value in the
debugger’s locals window
7. When you are confident your code is correct, compile your code using the Build icon (keyboard shortcut F7)
8. The debugger can be started from the Debug menu (keyboard shortcut ctrl-F5)
9. Test (and if necessary, debug) your code. You can single step through your code from the Debug menu (keyboard
shortcut F11). You can Step Over (keyboard shortcut F10) the call to your function sqrt( ) to see the retuned value
without stepping into the function. You can run the function without stepping (keyboard shortcut F5).
10. Get completion of this lab for your group after showing a tutor your compiled function returning the correct results
for the input arguments below:
sqrt_x = sqrt(0);
sqrt_x = sqrt(1);
sqrt_x = sqrt(25);
sqrt_x = sqrt(133);
sqrt_x = sqrt(4294967295); //extension
KEIL INTEGER TYPES (C167)
type range
char 0 -> 255
signed char -128 -> 127
short -32768 -> 32767
unsigned short 0 -> 65535
int -32768 -> 32767
unsigned int 0 -> 65535
long -2147483648 -> 2147483647
unsigned long 0 -> 4294967295
long long -9.2 x 1018
-> 9.2 x 1018
unsigned long long 0 -> 1.8 x 1019
Note: these are compiler specific. ANSI C rules are:
short <= int <= long
SQUARE ROOT ALGORITHM FLOWCHART
This algorithm calculates the square root of a number, given interval endpoints within which the square root lies. Base
your software on the following flowchart.
INPUT: x, where x is an unsigned long
INITIALISE: endpoint values a, b, such that a < b; the midpoint m, and the previous iterations midpoint.
WHILE LOOP: shown within a blue dashed rectangle.
EXIT CONDITIONS: shown within a green dashed rectangle.
OUTPUT: sqrt_x, where sqrt_x is an unsigned short. This value differs from the true sqrt(x) by less than 1.
Figure 3: Example flowchart of the function sqrt( ).