Embedded C workshop

By: Mostafa El-koumy
Day #1
Embedded

Introduction
?
o Introduction to Embedded C.
o Embedded Software Architecture.
o Memory usage.
o Embedded Development Environment.
o Interrupts.
o Keywords.
o Some Embedded Systems concepts.

INTRODUCTION
 Embedded Systems is all things around you which have
something called electronic brain to make some sort of
artificial intelligence.
 Embedded C is a prober subset of C language suitable for
Embedded systems, it defines only a new concept of
writing software.
 Using Embedded C, we should handle everything used in
the program like Memory Management, HW Registers,
interrupts, …. Etc.

MISRA RULES
 Motor Industry Software Reliability Association.
 Collaboration between engineering consultancies which
seeks to promote best practice in developing
Automotive Systems and other embedded systems.
 To this end MISRA publishes documents that provide
accessible information for engineers and management,
and holds events to permit the exchange of experiences
between practitioners.
 URL : www.misra.org.uk
 EX:

EMBEDDED SOFTWARE ARCHITECTURE

EMBEDDED SOFTWARE ARCHITECTURE (CON’T)

CODE FLOW
 All the code is running within infinite loop in main except:
 Initialization code.
 Interrupt handlers, interrupt service routines (ISR).
 The other code runs normally
int main (void)
{
intitializeModule();
sei();
while(1){
startApplication();
}
return 0;
}

BACKGROUND/FOREGROUND TASKS (LOW COST)

SOFTWARE MODELING
Function
C file
Module
Project
C file(s) H file(s)
SW
module
Uart.c
Uart.h
Uart_irq.c
Uart_cfg.h

MEMORY USAGE BY LINKER SCRIPT
 The HW Registers
 Stack space that grow down
 Local variables
 Functions return address
 Heap Space that grow up
 Zero default initialized variables
 Initialized with value by developer
I/O Addresses
Stack (grow down)
Heap (Grow up)
Un-initialized data
(.BSS)
Initialized data

DEVELOPMENT ENVIRONMENT
 IDE which has
 Text editor.
 Cross compiler produce machine language

 Development Kit

 In circuit Debugger (ICD)
 HW device connects to the microprocessor using JTAG/SWD
interface to support external control of the microprocessor
using debugger.
 Restrictions of debugging capabilities is specified by the
microprocessor.

 In circuit Emulator (ICE)
 HW device used to debug embedded SW. it replaces the
microprocessor with control over all the aspects of it and it
usually emulate all the microprocessor family.

PROGRAMMING PROCESS DIAGRAM

GPIO MODULE
Exercise
1

INTERRUPTS
 an interrupt is a signal to the processor emitted by
hardware or software indicating an event that needs
immediate attention. An interrupt alerts the processor
to a high-priority condition requiring the interruption of
the current code the processor is executing.
 Interrupt sources
 Internal peripherals.
 External interrupts.
 SW interrupts.
 Exception thrown by processors.

INTERACTIVE QUESTIONS
 Mask able interrupt?
 Non-Mask able interrupts?
 Level triggered external interrupt?
 Edge triggered external interrupt?
 Interrupt nesting?

INTERRUPT TIMING
 Interrupt latency?
 Context?
 Interrupt response?
 Interrupt recovery?

EMBEDDED KEYWORDS (INTERACTIVE)
 Scope and life time with keywords:
 Static local
 Static global
 Volatile
 Const
 Extern
 register

FUNCTIONS VS MACROS
 Macros in completely text replacement so it increase the
code size and duplications.
 Function is preferred.

MACROS VS INLINE FUNCTIONS
 In Inline functions Compiler substitute the function call
by function code like MACROS.
 MACROS is supported by preprocessor so all the IDEs
supports it.
 Inline is supported by some compilers.
 Inline function performs type checking but MACROs not.
 Inline function could be traced but MACROs not.
 Some compiler disable inline function when the its code
is large.

Exercise
2
UART MODULE

Thank you for
your attention!
Any Questions?

CONTACT DETAILS
 Mostafa El-koumy
 Embedded SW Developer
 mostafa.elkoumy@gmail.com

Embedded C workshop

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