1. Arm Programming in C Chapter 7
Sepehr Naimi

2. Topics
Data Types
Time Delays
Logic Operation in C

3. Languages High Level Languages C Language Low Level Languages
Easy to develop and update
C Language
Acceptable performance
Low Level Languages
High performance
Not portable
High Level Languages
(like VB)
C Language
Machine Language

4. A simple C program
Write a program that calculate the sum of {1,3,…,13,15}
#include <stm32f10x.h>
int main () {
unsigned int sum;
for (int i = 1; i <= 15; i+=2)
sum += i;
while (1);
return 0; }

5. Data Types
Data type
Size
Range
char
1 byte
-128 to 127
unsigned char
0 to 255
short int
2 bytes
-32,768 to 32,767
unsigned short int
0 to 65,535
long
4 bytes
-2,147,483,648 to 2,147,483,647
unsigned long
0 to 4,294,967,295
long long
8 bytes
-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
unsigned long long
0 to 18,446,744,073,709,551,615
The int data type is 32-bit in Arm. It is 16-bit in 16-bit and 8-bit processors.

6. ISO C99 integer data types
Size
Range
int8_t
1 byte
-128 to 127
uint8_t
0 to 255
int16_t
2 bytes
-32,768 to 32,767
uint16_t
0 to 65,535
int32_t
4 bytes
-2,147,483,648 to 2,147,483,647
uint32_t
0 to 4,294,967,295
int64_t
8 bytes
-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
uint64_t
0 to 18,446,744,073,709,551,615

7. What is the difference between signed and unsigned integers?
Data types (cont.) c
char c;
int8_t c;
short int a1;
int16_t a1;
long lng;
int32_t lng;
uint16_t a;
unsigned short a;
lng a1 a
What is the difference between signed and unsigned integers?

8. Signed vs. unsigned Unsigned Signed Unsigned Multiplication:
uint32_t a1 = 5;
uint32_t a2 = 3;
uint32_t a3 = 2;
b = (a1 * a2) / a3;
int32_t a1 = 5;
int32_t a2 = 3;
int32_t a3 = 2;
b = (a1 * a2) / a3;
Unsigned Multiplication:
Signed Multiplication:
MUL Rd,Rn,Op2
UMULL RdLo,RdHi,Rn,Rm
SMULL Rdlo,Rdhi,Rm,Rn
Unsigned Division:
Signed Division:
UDIV Rd, Rm, Rn
SDIV Rd,Rm,Rn

9. Time Delays in C You can use for to make time delay
void delay(void) {
volatile unsigned int i;
for(i = 0; i < 42150; i++)
{ } }
If you use for loop
The clock frequency can change your delay duration!
The compiler has direct effect on delay duration!

10. Bit-wise logical operators
& | ~

11. Shift operations in C data >> number of bits to be shifted right
data << number of bits to be shifted left
>> 3
<<2

12. Setting a bit in a Byte to 1
We can use | operator to set a bit of a byte to 1
xxxx xxxx |
xxx1 xxxx
xxxx xxxx
| 1 << 4
xxx1 xxxx OR
GPIOA->ODR |= (1<<4); //set bit 4 (5th bit) of GPIOA->ODR

13. Clearing a bit in a Byte to 0
We can use | operator to set a bit of a byte to 1
xxxx xxxx
&
xxx0 xxxx
xxxx xxxx
& ~(1 << 4)
xxx0 xxxx OR
GPIOB->ODR &= ~(1<<4); //clear bit 4 (5th bit) of GPIOB->ODR

14. if( ((GPIOA->IDR & (1<<5)) != 0) //check bit 5 (6th bit)
Checking a bit in a Byte
We can use & operator to see if a bit in a byte is 1 or 0
xxxx xxxx
&
x 0000
xxxx xxxx
& (1 << 4)
x0 0000 OR
if( ((GPIOA->IDR & (1<<5)) != 0) //check bit 5 (6th bit)