Software engineering, program management

The problem  Software is expensive to design! – Industry estimates put software development labor costs at 1.5 hours per machine instruction – Software developers are expensive labor – Most "real" programs contain thousands, if not millions of lines of code  The quality of much software and most documentation is poor

The problem  Even after extensive testing, software frequently has bugs – Testing can prove the presence of bugs, but testing can (almost) never prove the absence of bugs! – Testing and debugging software can take as much or more time than the original planning and writing  Most new software is completed later than forecast (2x or 3x longer is common)  Programming can be tedious, boring work

The problem  The design process – Software development, as any engineering effort, should be based around a logical design methodology whether for a lab assignment or as part of a large SW design team

The problem Need Concept Decomposition Specification Design Test / Validation Production Deployment Maintenance Disposa

Programmer's "goals" what's important?  Write the shortest program – Uses less memory, so hardware requirements are less – Often trading expensive human effort for inexpensive hardware costs – Encourages programming "tricks"

Programmer's "goals" what's important?  Write the fastest program – Get the program's execution done as quickly as possible – Not always an important goal in embedded systems – More payoff from developing and implementing an efficient algorithm – Use profiling as a guide to optimizing the already good algorithm

Programmer's "goals" what's important?  Write an easily understood program – The programmer and others must be able to understand the function of the instructions in the program – Complex programs are hard to modify and maintain – Good documentation – KISS principle

Programmer's "goals" what's important?  Write an easily modified program – Be able to change it to cope with changing environments – Requires planning and effort during the design phase – Effort is extremely cost effective compared to redesign effort – Focus on long-term success

Programmer's "goals" what's important?  Meet the schedule – Avoid the vaporware syndrome – Organize and plan for changes – Failure can mean loss of market share

Program design  The design process lends itself to an iterative problem decomposition in a divide-and-conquer approach  Decompose overall task into smaller subtasks that can be written and tested independently

Program design

 Avoid spaghetti code and designs – Each module should have single entry / exit points

Program design  Structured programming uses 3 basic control structures

Documentation  Good documentation is mandatory for good code This provides information needed by humans to understand the operation of the program and enable efficient maintenance and modification  For a given code segment / block / function, well thought out, detailed comments in the “header” can help reduce the need for line-by-line comments within the code itself

Documentation  Programs can be over or under documented  Examples: – Wrong: LDAA #$56 ; load ACCA with $56 – Right: LDAA #$56 ; initialization word for ; DDRC -- bits 1,2,4,6 ; are outputs

Documentation  Each code segment / block / function should include comments that … – Identify the routine’s name and function – Who wrote it and when – Describe the algorithm being implemented – Explain the parameters being passed to and from the routine – List other routines that call this routine or are called by this routine CONTD

Documentation – Describe register and memory requirements -- which locations are altered? – Give the modification history – Do not overwhelm the reader (particularly in-line comments)  Software written for the labs and design projects is expected to follow these guidelines! – For a good example, see the code included with the sample lab report on the WI web page

Documentation  Main routine should be mostly calls to subroutines – If something takes more than a few instructions, don’t put it directly in the main routine – make it a subroutine – Main routine will usually be an infinite loop – Example: ;******************************** ; Thermometer: This program reads an ; analog value from a temperature sensor ; every 0.5 seconds, and displays the ; temperature on an LCD display. ;********************************

Documentation ORG $B600 Thermometer: lds #$1FF ; initialize stack pointer jsr InitSystem ;initialize the system Loop: jsr GetAnalogValue ; get A/D value from ; temp sensor jsr ConvertTemp ; determine the ; temperature jsr DisplayTemp ; display it on LCD jsr Delay0P5 ; delay for 0.5 seconds bra Loop ; repeat

Documentation  Include a header with each subroutine: ;******************************** ; Convert_Temp: This routine converts ; an analog value (assumed to be an 8-bit ; binary fraction between 0 and 1) to a ; Fahrenheit temperature using the formula ; temp = (value * 180) + 32 ; Input: ACCA = 8-bit analog value ; Output : ACCA = temperature ; Registers modified: CCR ;********************************

Documentation Convert_Temp: pshb ; save ACCB ldab #180 ; calculate temp mul ; = (value * 180) + 32 adca #32 ; ACCA = temp pulb ; restore ACCB rts ; return

Summary  Programs should be well-designed and well- documented  Use a modular design – Each subroutine should perform a single function – Subroutine interfaces should be clearly defined  Focus on making programs easy to understand and easy to maintain – Bonus: They’re often easier to debug CONTD

Summary – Avoid programming “tricks” unless they are truly needed for performance or memory requirements – If you need to use “tricks” -- document them!  Time spent on design (before coding) is usually a good investment