Embedded firmware

• responsible for controlling the various
peripherals of the embedded hardware
• stored in a permanent memory (ROM)

Designing Embedded firmware
• requires understanding of the particular embedded
product hardware,
• like various component interfacing,
• memory map details,
• I/O port details,
• configuration and register details of various
hardware chips used and
• some programming language (either low level
Assembly Language or High level language like
C/C++ or a combination of the two)

There exist two basic approaches for the design
and implementation of embedded firmware,
namely;
The Super loop based approach
The Embedded Operating System based
approach
The decision on which approach needs to be
adopted for firmware development is purely
dependent on the complexity and system
requirements

Embedded firmware Design Approaches – The Super
loop
Suitable for applications that are not time critical
Very similar to a conventional procedural programming where the
code is executed task by task
The tasks are executed in a never ending loop.
A typical super loop implementation will look like:
1. Configure the common parameters and perform initialization
for various hardware components memory, registers etc.
2. Start the first task and execute it
3. Execute the second task
4. Execute the next task
5. :
6. :
7. Execute the last defined task
8. Jump back to the first task and follow the same flow

void main ()
{
Configurations ();
Initializations ();
While (1)
{
Task 1 ();
Task 2 ();
//:
//:
Task n ();
}
}
The only way to come out of this loop is either hardware reset or
an interrupt assertion

Embedded firmware Design Approaches – Embedded
OS based Approach
The embedded device contains an Embedded Operating
System which can be one of:
• A Real Time Operating System (RTOS)
• A Customized General Purpose Operating System
(GPOS)
• The Embedded OS is responsible for scheduling the
execution of user tasks and the allocation of system
resources among multiple tasks
• Involves lot of OS related overheads apart from
managing and executing user defined tasks

Microsoft® Windows XP Embedded is an
example of GPOS for embedded devices
Point of Sale (PoS) terminals, Gaming Stations,
Tablet PCs etc are examples of embedded devices
running on embedded GPOSs
‘Windows CE’, ‘Windows Mobile’,‘QNX’,
‘VxWorks’, ‘ThreadX’, ‘MicroC/OS-II’,
‘Embedded Linux’, ‘Symbian’ etc are examples of
RTOSs employed in Embedded Product
development
Mobile Phones, PDAs, Flight Control Systems etc
are examples of embedded devices that runs on
RTOSs

Embedded firmware Development Languages/Options
Assembly Language
High Level Language
Subset of C (Embedded C)
Subset of C++ (Embedded C++)
Any other high level language with supported Cross-
compiler
Mix of Assembly & High level Language
Mixing High Level Language (Like C) with Assembly Code
Mixing Assembly code with High Level Language (Like C)
Inline Assembly

Embedded firmware Development Languages/Options
– Assembly Language
Assembly Language’ is the human readable notation of
‘machine language’
‘machine language’ is a processor understandable
language
Machine language is a binary representation and it
consists of 1s and 0s
• Assembly language programming is the process of
writing processor specific machine code in
mnemonic form, converting the mnemonics into
actual processor instructions (machine language)
and associated data using an assembler

The general format of an assembly language
instruction is an Opcode followed by Operands
The Opcode tells the processor/controller what to
do and the
Operands provide the data and information
required to perform the action specified by the
opcode
Each line of an assembly language program is
split into four fields as:
LABEL OPCODE OPERAND COMMENTS

;####################################################################
; SUBROUTINE FOR GENERATING DELAY
; DELAY PARAMETR PASSED THROUGH REGISTER R1
; RETURN VALUE NONE
; REGISTERS USED: R0, R1
;####################################################################
DELAY: MOV R0, #255 ; Load Register R0 with 255
DJNZ R1, DELAY ; Decrement R1 and loop till R1= 0
RET ; Return to calling program

• The Assembly language program written in assembly code is
saved as .asm (Assembly file) file or a .src (source) file or a format
supported by the assembler
• The software utility called ‘Assembler’ performs the translation of
assembly code to machine code
• Assembling of each source file generates a corresponding object
file. The object file does not contain the absolute address of where
the generated code needs to be placed (a re-locatable code) on the
program memory
• The software program called linker/locater is responsible for
assigning absolute address to object files during the linking
process
• A software utility called ‘Object to Hex file converter’ translates
the absolute object file to corresponding hex file (binary file)

Embedded firmware Development Languages/Options – Assembly Language –
Source File to Hex File Translation
Assembly language to machine language Conversion process

Embedded firmware Development Languages/Options – High
Level Language
• The embedded firmware is written in any high level
language like C, C++
• A software utility called ‘cross-compiler’ converts the
high level language to target processor specific machine
code
• The cross-compilation of each module generates a
corresponding object file. The object file does not contain
the absolute address of where the generated code needs to
be placed (a re-locatable code) on the program memory
• The software program called linker/locater is responsible
for assigning absolute address to object files during the
linking process
• A software utility called ‘Object to Hex file converter’
translates the absolute object file to corresponding hex file
(binary file)

Embedded firmware Development Languages/Options – High Level Language –
Source File to Hex File Translation
Source File 1
(.c /.c++ etc)
(Module-1)
Module
Cross-compiler
Source File 2
(.c /.c++ etc)
(Module-2)
Module
Cross-compiler
Object File 1
Object File 2
Library Files
Linker/
Locator
Absolute Object File
Object to Hex File
Converter
Machine Code
(Hex File)
High level language to machine language conversion process

Embedded firmware Development Languages/Options –
Mixing of Assembly Language with High Level Language
Certain situations in Embedded firmware development may require the
mixing of Assembly Language with high level language or vice versa.
Interrupt handling, Source code is already available in high level
languageAssembly Language etc are examples
High Level language and low level language can be mixed in three different
ways
Mixing Assembly Language with High level language like ‘C’
Mixing High level language like ‘C’ with Assembly Language
In line Assembly
The passing of parameters and return values between the high level and low
level language is cross-compiler specific

High Level Language – ‘C’ V/s
Embedded C
Embedded C can be considered as a subset of conventional ‘C’
language
Embedded C supports all ‘C’ instructions and incorporates a few
target processor specific functions/instructions
The standard ANSI ‘C’ library implementation is always tailored to
the target processor/controller library files in Embedded C
The implementation of target processor/controller specific
functions/instructions depends upon the processor/controller as well
as the supported cross-compiler for the particular Embedded C
language
A software program called ‘Cross-compiler’ is used for the
conversion of programs written in Embedded C to target
processor/controller specific instructions

High Level Language Based Development – ‘Compiler’ V/s
‘Cross-Compiler’
 Compiler is a software tool that converts a source code written in a high level language on top
of a particular operating system running on a specific target processor architecture (E.g. Intel
x86/Pentium).
 The operating system, the compiler program and the application making use of the source
code run on the same target processor.
 The source code is converted to the target processor specific machine instructions
 A native compiler generates machine code for the same machine (processor) on which it is
running.
 Cross compiler is the software tools used in cross-platform development applications
 In cross-platform development, the compiler running on a particular target processor/OS
converts the source code to machine code for a target processor whose architecture and
instruction set is different from the processor on which the compiler is running or for an
operating system which is different from the current development environment OS
 Embedded system development is a typical example for cross-platform development where
embedded firmware is developed on a machine with Intel/AMD or any other target processors
and the same is converted into machine code for any other target processor architecture (E.g.
8051, PIC, ARM9 etc).
 Keil C51compiler from Keil software is an example for cross-compiler for 8051 family
architecture

Embedded firmware

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