1. Programming Embedded Systems in C++
Day 1: C++ for Embedded Programming 
19 May 2014 Colin Walls, Mentor Graphics

2. [ # ]
This is what a question slide will look like. Please answer in the chat.
Also, questions to me start with ?

3. Agenda
Monday: C++ for Embedded Programming Tuesday: C to C++ Migration Strategy Wednesday: C++ and a Real Time Operating System Thursday: Case study #1 Friday: Case Study #2

4. Why is C++ Not More Widely Used?
Conservatism
“If it ain’t broke, don’t fix it”
Early attempts failed
bad tools
inappropriate programming practice
Fears
code bloat
performance
dynamic memory

5. [ 1 ]
Who is already using C++ for embedded applications?

6. The Genealogy of C++
BCPL and B
K & R C
other OO Cs
C++
ANSI C
Java

7. The Genealogy of C++ CPL BCPL and B Algol Simula 67 Fortran IV K & R C
other OO Cs
C++
ANSI C
Java

8. Limitations of C
C is extremely powerful and flexible and can therefore be dangerous
It has low level capabilities (which are useful for embedded)
There are many pitfalls for the unwary
Programmers need to be very methodical and disciplined
Programmers need to understand how the program behaves at low and high levels
Large projects are thus hard to maintain
Programmers need an expert knowledge of the application

9. [ 2 ]
What other languages make sense for embedded system programming?

10. How C++ May Help
Encapsulates and hides areas of high expertise from non-experts into “objects”
“An expert is a man who has made all the mistakes that can be made, in a very narrow field.” - Nils Bohr
Objects can be used intuitively by non-experts to implement conceptual designs at a high-level
Case study …

11. C++ Language Overview End of line comment notation
<code> // <comment>
Allows nesting
Eases “commenting out”
Dynamic memory allocation operators
new and delete
mostly equivalent to malloc() and free()
Mandatory function prototypes

12. C++ Language Overview Function parameter default values
void fun(int w, int x, int y=1, int z=3) {
... }
fun(1, 2, 3, 4);
fun(1, 2, 3);
fun(1, 2);
fun(1); // error
fun(1, 2,, 4) // error

13. C++ Language Overview Function parameter default values
void fun(int w, int x, int y=1, int z=3) {
... }
fun(1, 2, 3, 4);
fun(1, 2, 3);
fun(1, 2);
fun(1); // error
fun(1, 2,, 4) // error

14. C++ Language Overview Function parameter default values
void fun(int w, int x, int y=1, int z=3) {
... }
fun(1, 2, 3, 4);
fun(1, 2, 3);
fun(1, 2);
fun(1); // error
fun(1, 2,, 4) // error

15. C++ Language Overview Function parameter default values
void fun(int w, int x, int y=1, int z=3) {
... }
fun(1, 2, 3, 4);
fun(1, 2, 3);
fun(1, 2);
fun(1); // error
fun(1, 2,, 4) // error

16. C++ Language Overview Function parameter default values
void fun(int w, int x, int y=1, int z=3) {
... }
fun(1, 2, 3, 4);
fun(1, 2, 3);
fun(1, 2);
fun(1); // error
fun(1, 2,, 4) // error

17. C++ Language Overview Function parameter default values
void fun(int w, int x, int y=1, int z=3) {
... }
fun(1, 2, 3, 4);
fun(1, 2, 3);
fun(1, 2);
fun(1); // error
fun(1, 2,, 4) // error

18. C++ Language Overview Reference parameters Pointers
void swap(int& a, int& b) {
int temp = a;
a = b;
b = temp; }
...
swap(x, y);
Pointers
void swap(int *a, int *b) {
int temp;
temp = *a;
*a = *b;
*b = temp; }
...
swap(&x, &y);

19. C++ Language Overview Inline functions small functions faster
use inline keyword
or include code in class definition
only advice to the compiler

20. C++ Language Overview Function overloading
multiple functions with same name
different parameter number/types
max(int a, int b, int c);
max(int a, int b);
max(float x, float y);
max(1, 2);
max(3.4, 5.6);
max(1.1, 2.2, 3.3); // error

21. C++ Language Overview Typesafe linkage
function names “mangled” to encode parameter types
max(int, int) becomes [say] max_int_int()
max(int, int, int) becomes max_int_int_int()
linker becomes “C++ aware”

22. Object Oriented Features
Concept of class is key
similar to a C structure
contains data and code
code/data may be hidden (private)
class is a new data type
operators may be defined
automatic constructor/destructor
inheritance

23. [ 3 ]
When you are coding, what should be your #1 priority?

24. Templates
template <class X> void swap(X& x, X& y) { X temp; temp = x; x = y; y = temp; }
int i, j; float a, b; ... swap(a, b); swap(i, j);

25. Templates What is the “cost”? In theory, no overhead
code is generated when required
compilers process one module at a time
instantiations are local to a module
duplicate code results
solution is “smart” linker
also deals with out-of-line inline functions

26. Efficiency - Templates
FILE1.CC
max(int, int);
max(char, char);
FILE2.CC
max(int, int);
max(char, char);
Local Copy
max(int, int);
Local Copy
max(int, int);
Local Copy
max(char, char);
Local Copy
max(char, char);

27. Efficiency - Templates
60K unique
50K common
330K total linked
image size
100K duplicate
60K unique
50K common
Normal Link
60K unique
50K common

28. Efficiency - Templates
60K unique
50K common
330K total linked
image size
100K duplicate
Optimised
Link
60K unique
50K common
Link
230K total linked
image size
60K unique
50K common

29. Exception Handling Efficient exit from structured code
Use to deal with error conditions
Extra code generated
must be able to turn EHS off

30. Exception Handling
catch
try
catch
throw
catch
catch
throw
catch
catch

31. Exception Handling try { // application code } catch (int n)
// exception handling code
throw 99;

32. Exception Handling Simple error handling
have no catch statement – use terminate()
have generic handler:
catch (...) {
... }

33. Class Layout for Inheritance
class BaseClass { ... };
class DerivedA : virtual public BaseClass { ... };
class DerivedB : virtual public BaseClass { ... };
class DerivedC : virtual public BaseClass { ... };
class DerivedD : virtual public BaseClass { ... };
class Mderived : DerivedA, DerivedB, DerivedC, DerivedD { ... };
MDerived
DerivedA
DerivedB
DerivedC
DerivedD
Duplicate copies
of BaseClass
subobject

34. Class Layout for Inheritance
class BaseClass { ... };
class DerivedA : virtual public BaseClass { ... };
class DerivedB : virtual public BaseClass { ... };
class DerivedC : virtual public BaseClass { ... };
class DerivedD : virtual public BaseClass { ... };
class Mderived : DerivedA, DerivedB, DerivedC, DerivedD { ... };
MDerived
DerivedB
DerivedC
DerivedD
BaseClass
DerivedA
Only a single copy
of BaseClass
subobject

35. Language Extensions
packed and unpacked
interrupt
asm
volatile

36. Approaches Don’t program like a PC Embedded C++
every PC is the same
memory infinite and free
processor power excess
speed of operation the requirement
every embedded system is different
top-down, heavily OO approach leads to overheads showing up too late
Embedded C++
Encapsulation of expertise
Beyond C++

37. Agenda
Monday: C++ for Embedded Programming Tuesday: C to C++ Migration Strategy Wednesday: C++ and a Real Time Operating System Thursday: Case study #1 Friday: Case Study #2

38. Question review ...

39. [ Review - 2 ]
What other languages make sense for embedded system programming?

40. [ Review - 3 ]
When you are coding, what should be your #1 priority?

41. Colin Walls