Description
1. Objectives
In this lab, you will learn AVR programming on
memory access, and
stack and function.
2. Tasks
2.1 Task 1: String to Integer Conversion (Due Week 5)
The C program in Figure 1 implements the function of converting a string to an integer.
The string is given in main() and its integer is obtained by calling function atoi().
Manually translate the program into an assembly program with atoi implemented as a
function. Assume the string is stored in the program memory and that an integer takes
two bytes.
int main(void) {
char s[ ] = “12345”;
int number;
number = atoi(s);
return 0;
}
int atoi(char *a) {
char i;
char c;
int n;
n = 0;
c = *a;
for (i=1; ((c >=’0′) && (c<='9') && (n<65536)); i++){
n = 10 * n + (c -'0');
c = *(a+i);
}
return n;
}
Figure 1 string_to_number.c
2.2 Task 2: Positional Division (Due Week 6)
Hand-division is a positional division that uses a series of left shifts, magnitude checks
and multiple subtractions to get the result. The program in Figure 2 describes the
positional division algorithm for the 16-bit binary division. Manually translate the
program into an assembly function. Assume the dividend and the divisor are stored in
the program memory and that the quotient is saved in the data memory. To test your
design, you need to create a caller to the function.
int posdiv(unsigned int dividend, unsigned int divisor) {
unsigned int quotient;
unsigned int bit_position = 1;
quotient = 0;
while ((dividend > divisor) && !(divisor & 0x8000)) {
divisor = divisor << 1;
bit_position = bit_position << 1;
}
while (bit_position > 0) {
if (dividend >= divisor) {
dividend = dividend – divisor;
quotient = quotient + bit_position;
}
divisor = divisor >> 1;
bit_position = bit_position >> 1;
}
return quotient;
}
Figure 2: binary_positional_division.c
Note: Each task is worth 6 marks. All your programs should be well commented
and easy to read. Up to 1 mark will be deducted for each program without proper
and sufficient comments.
