Embedded system
It is a computer hardware, software, other parts designed to perform a specific function component within larger system - in cars, air/spacecraft.
Embedded software in almost every electronic devices like;.. watches, VCR's, cellular phones, microwaves, thermostats and each embedded system is unique, with specialized
hardware and specialized software.
Developing Software for Embedded Systems
- Steps involved in preparing embedded software similar to
general programming
- Follow five steps in Software Design Process
- Use Spiral Model
- Decide on programming language (C)
- Know capabilities/limitations of processor/compiler
Main difference is that target hardware platform is unique
- Leads to additional software complexity
- Software Engineer must be aware of software build process
Embedded Software Development Process
Software development is performed on a host computer
- Compiler, Assembler, Linker, Locator, Debugger
- Produces executable binary image that will run on Target Embedded System
Programming Embedded Systems
Embedded Systems Programming requires a more complex software
build process
- Target hardware platform consists of
- Target hardware (processor, memory, I/O)
- Target hardware (processor, memory, I/O)
- Run time environment (Operating System/Kernel)
Target hardware platform contains only what is needed for final
deployment
- Target hardware platform does not contain development tools (editor,
compiler, debugger)
- Target hardware platform is different from development platform
- Development platform, called the Host Computer, is typically a general purpose
computer
- Host computer runs compiler, assembler, linker, locator to create a binary
image that will run on the target embedded system
Process for Developing Embedded Software
To develop software for a General Purpose Computer
- Create source file
- Type in C code
- Build: compile and link
- Execute: load and run
To develop software for an embedded system
- Create source file (on Host)
- Type in C code (on Host)
- Compile/Assemble: translate into machine code (on Host)
- Link: combine all object files and libraries, resolve all symbols (on Host)
- Locate: assign memory addresses to code and data (on Host)
- Download: copy executable image into Target processor memory
- Execute: reset Target processor
Compiling Embedded Systems
- Compiler translates program written in human-readable language into
machine language
- Source Code --> Object file
- Object file is binary file that contains set of machine-language
instructions (opcodes) and data resulting from language translation
process
Machine-language instructions are specific to a particular processor
- Can the host computers compiler be used to compile a program to run
on the target computer?
- A Native-compiler runs on a computer platform and produces code for
that same computer platform
- A Cross-compiler runs on one computer platform and produces code
for another computer platform.
Assemblers/Interpreters for Embedded Systems
- In some cases, a compiler is not used
- Assembler performs one-to-one translation from human-readable
assembly language mnemonics to equivalent machine-language
opcodes
Interpreter constantly runs and interprets source code as a set of
directives
- Performs syntax checking as program is typed in
- Result is slow performance - can be ~1000x slower than an equivalent
compiled language
- Interactive capability provides more feedback -- easier to learn
Handyboard Interpreter
- Handyboard runs a C interpreter called Interactive C
- C code is compiled into custom language
- Custom language is interpreted by p-code
- In interactive mode, syntax checked in IC console window
E.g., To clear HB screen, type in following line:
printf (“\n”);
Linking Embedded Systems
- The Linker combines object files (from compiler) and
resolves variable and function references
- Source code may be contained in >1 file, which must be
combined
- Resolve variables which may be referenced in one file and
defined in another file
- Resolve calls to library functions, like sqrt
- May include operating system
ï Linker creates a relocatable version of the program
- Program is complete, except no memory addresses assigned
Locating Embedded Systems
- A Locator is the tool that performs the conversion from
relocatable program to executable binary image
- The Locator assigns physical memory addresses to code
and data sections within the relocatable program
- The Locator produces a binary memory image that can be
loaded into the target ROM
- In contrast, On General Purpose Computers, the operating
system assigns the addresses at load time
Downloading and Executing Your Program
- Once a program has been successfully compiled, linked,
and located, it must be moved to the target platform
- Download the binary image to the embedded system
- Executable binary image is transferred and loaded into a
memory device on target board
- Can be loaded into ROM via a device programmer, which burns a chip that is then re-inserted into the embedded
system
- Handyboard must be put into bootstrap download mode first,
then data can be transferred via serial port into memory
- Your program will then execute when you reset the
processor, or apply power to the embedded system
Review Process for Developing Embedded Software
- To develop software for an embedded system
- Create source file (on Host)
– Type in C code (on Host)
- Compile/Assemble: translate into machine code (on Host)
- Link: combine all object files and libraries, resolve all symbols (on Host)
- Locate: assign memory addresses to code and data (on Host)
- Download: copy executable image into Target processor memory
– Execute: reset Target processor
Process for Developing Handyboard Software
- To develop software for the Handyboard
- Create source file (on Host)
- Type in C code (on Host)
- Download file:
» Compile: translate into custom interpreted language (on Host)
» Locate: assign memory locations (on Host)
» Download: transfer interpreted language via serial board to HB
- Execute:
» Reset HB which runs “main” function
» P-code interprets custom language
Debugging Embedded Software
- Now that the software has been downloaded to the target
processor, how do we know if it is working?
- Run-time errors are not as obvious
ñ Most embedded systems do not have a screen
- When a program fails, usually causes the processor to crash
or lock-up
- Logic errors
- If program runs, is it performing the correct steps?
