1. An Introduction to Embedded Software Architecture and Design
Class 4: From Architecture to Implementation
December 4, 2014 Jacob Beningo, CSDP

2. Course Overview Introduction to Embedded Software Architecture
Software Architecture using UML
Understanding Embedded Software Architectures
From Architecture to Implementation
Software Architecture of a UAV and Review

3. Session Overview Review of the Example Problem Architecture to Design
Design to Implementation
Tips and Tricks

4. An Example Problem Review
Remote firmware updates
System requires periodic firmware updates in the field without the use of specialized hardware
Must blink an led in this mode
Seamless ability to switch between app and update mode
System requires the ability to be updated via UART
simulates radio connectivity

5. Architecture to Design
Software Architecture
Provides us different views of software in regards to
User interactions with the system
Environmental conditions
Timing
System states
Etc
Relate to requirements of the system
Does NOT provide low level details

6. Architecture to Design

7. Architecture to Design
What is included in the design phase?
Detailed planning of the software to the lowest levels!
Such as …..
Flowcharting
Function definitions
Variable naming
Task declarations
API’s

8. Architecture to Design
Flow Charts
Most common design element
Consists of
Entry point
Conditionals
Actions
Exit point
Keep them simple!
Highlight enum and const

9. Architecture to Design
Flowcharting of the boot-loader

10. Architecture to Design
API’s
Critical to creating reusable software
Defines a common interface that can be used from one project to the next
Identifies useful peripheral features
If adhered to code can be reused and ported with ease
Examples include ….

11. Architecture to Design
API’s continued
Digital Input / Output API’s
EEPROM

12. Architecture to Design
Operating System Selection
What did the architecture dictate?
Polling
Interrupt Driven (Event-driven)
Cooperative Scheduling
Real-time Operating System
Hybrid systems

13. Architecture to Design
Coding Standards
Design stage is the perfect time to pick a coding standard!
Sets the tone for how the firmware should look and feel
Sets the do’s and don’t
Sets the best practices to follow
Hopefully verifiable by tools

14. Design to Implementation
Implementation is easy!
Architecture for the general roadmap
Design for the detailed flowcharts and layout
What could possibly go wrong?

15. Design to Implementation
Bootloader Implementation
// When the checksum has completed and the timer has expired for waiting for a // programming tool to respond, perform the branch checks.
if((Checksum_Complete == TRUE) && (StartUpTmr == EXPIRED)) {
if((*ResetVector != 0xFFFF) && // Does app reset vector exist?
(Status != 'B') && // EEPROM status set?
(Boot_ToolPresent != TRUE) && // Tool present?
(Checksum_Valid != FALSE)) // Checksum valid?
App_LoadImage(); }
else
Boot_LoadImage();

16. Design to Implementation
Tip #1 Limit Function Complexity
Cyclomatic Complexity
Kolmogorov complexity
Function points

17. Design to Implementation
Tip #2 – Use Assertions

18. Design to Implementation
Tip #3 – Document Code Thoroughly
Function Inputs
Function Outputs
Function use and behavior
Related Functions
Plenty of comments on what it does
Maintainers and future self will thank you
Use tools like Doxygen to generate documentation from code comments

19. Design to Implementation
Tip #4 – Avoid the use of Global Variables
Encapsulate variables
Use data hiding
Object oriented design
Prevents data corruption
Reduces reentrancy issues
Use static to declare local variables
Use static to declare private functions

20. Design to Implementation
Tip #5 – Use Descriptive Naming Conventions
Don’t use abbreviations but the whole descriptive word!
If you use abbreviations then create a lookup table
Call it what it is and don’t be cryptic! (Use long variable names)
Use broad terms first then get specific
Choose naming conventions and be consistent!
Develop a coding standard to keep track of your conventions so that future you or maintainer can understand

21. Additional Resources Download Course Material for Edraw UML Templates
Updated C Doxygen Templates
Misc Papers and Websites for further reading
From under
- Blog and Articles > Software Techniques > CEC Software Architecture Materials

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