Embedded System - Unit II (Prepared by N.Shanmugasundaram)

Embedded SystemUnit II – Mixing C & Assembly

Prepared by

Prof. N.ShanmugasundaramHOD / ECE, VVCET.

Programming Embedded system can be accomplished

in three different ways, by using programming languages like …

1. High level languages (like C, C++, Java…)

2. Assembly language (using Mnemonics, Eg. ADD, MOV, etc.)

3. Machine level language (using OPCODES, Eg. 80H for ADD B)

Embedded System – Unit II

Advantages of different level programming …

High level language (like C ) i) easy understandable program ii) portability into diff processor

Assembly level language i) compact code (compared to C) ii) access to the special features of

the processor hardware.

Machine level language i) Highly compact code ii) Fast execution



Data Type Conversion


Manipulating Bits in Memory


Testing of Bits


Setting, Clearing and Inverting of Bits


Extracting of Bits


Inserting of Bits


Manipulating of Bits in I/O Ports


Write-only I/O Ports


Ports differentiated by Sequential Access


Ports differentiated by Bits in written data


Accessing Memory mapped I/O Devices

Most modern microprocessors are capable of addressing GBs of Memory, but embedded systems need only a few KBs of memory.

By assigning few unused memory address to I/O devices, these devices can be accessed as if a memory is being accessed.

A typical example of memory mapped I/O device is Display buffer (each character position in screen is assigned with one / more unique address).

In IBM-PC, color display buffer is mapped with memory address B8000H.

Each charater is assigned with 2 bytes, first byte for ASCII code of that character and second byte for the foreground and back ground color information.

The address of the first byte of a specific row & column is calculated as

B8000H + 2 (80 x Row + Column)


Accessing data through a pointer

In C,

We create a variable (ie., allocate memory for it) by declaring it;And then manipulate its content by referring to its identifier.

Example: int a;a = 5;

Alternate method to access a memory location is by using a pointer(Pointer is a variable that holds an address of memory location)

Example: int a, b;int *c ;

a = 5 ;c = &a;b = *c;

Typical programming to access display buffer through pointer variable is ...

Declarationchar *p ; /* “p” is a pointer to a char */

Initializationp = (char *) (0xB8000 + 2 * (80 * row + col)) ; /* p is intialized */

Declaration & Initializationchar *p = (char *) (0xB8000 + 2 * (80 * row + col)) ; /* declaration & initialization */

Assigning a value to pointer variable*p = ‘ A ‘ ; /* char ‘A’ is assigned to addr of p */



To display a text on screen; we can use a Pointer.


Structures


Packed Structures


Bit Fields

Embedded System - Unit II (Prepared by N.Shanmugasundaram)

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