Software Reuse: Software Design

Software Design

This continues on from my posts on Software Architecture and Operating Systems. The basis of Software Design for Embedded Systems is ensuring that you implement the required features within the available hardware. A lot of people forget that second point. I have found there are many more opinions on what you “Should Do” than there are helpful ways of assessing what you “Can Do” and how likely it is to be successful. Way too much of the conversation is like the picture below.

 

Software Programming

Software – You’re Doing It Completely Wrong!

Unlike a typical Computer Science project, there are hard and fast restrictions on the system resources in a Small Embedded System. Some of the constraints to consider are:

 

  • RAM
  • FLASH or program storage space
  • Clock Speed for both the peripherals and the main processor
  • Power Consumption
  • IO and peripherals
  • Latency requirements

 

If we have selected and Operating System then we also have constraints from that choice:

 

  • How to tasks or modules communicate?
  • How is data protected from simultaneous access by foreground and background tasks?
  • What is the worst case latency for a task or interrupt response?
  • Can I meet the peak execution demand with the processor, Software Architecture and Operating System?
  • What design methodology will I use?
  • How will I test?

 

Software Design Methodology

This is also a pretty big area. For now we will focus on the primary methods that are used to manage more complex projects.

 

State Machine

The first and most important is the State Machine, originally known as the Finite State Machine. It was an invention of Hewlett Packard and many were surprised that Intel beat them to the first microprocessor given that the State Machine was one of the breakthrough concepts that made that possible. At it’s core, a State Machine defines the states a system or sub-system can be in and the conditions under which it moves from one state to another. Below is a State Machine for estimating the charge left in a rechargeable battery. We design a lot of battery powered equipment so this is a common design element for us.

 

Finite State Machine

State Machine

One big advantage of a State Machine is that it can be easily designed to operate in a polled environment where very little processor time is required until a transition condition is achieved. This allows very complex systems to operate without needing a larger processor.

 

Test Driven Development

Test Driven Development is the next important Software Design Methodology to consider. In this case the system is analysed and the test requirements identified. The tests are written and then the code is written and debugged until it passes the tests. If requirements change, then update the tests to match and debug until the code passes. Code is refactored once is passes all tests.

 

The big advantage of Test Driven Development is that you think about test up front and that generally leads to simpler designs that are easier to maintain. You also always have a full test suite to ensure changes made don’t have side effects that cause other features to misbehave. The tests pick this up automatically.

 

The big disadvantage is that you might write tests then decide to change direction and have to recreate those. These is also interaction between the system call structure and the test suite so you need to do more detailed design up front. But particularly in mission critical applications, always having an up to date test suite is a big advantage.

 

Rapid Application Development

The final consideration is whether you will use a visual coding or modelling system. For Windows Software we are big fans of the Embarcadero toolset, formerly under the Borland brand. These support Rapid Application Development or RAD as it is known. The tools create forms and provide the software skeleton to go with them automatically managing class members and access functions for you. This way you can focus on the application specific code. We find their C++ toolset one of the most productive to create application with.

 

These systems are generally used on general purpose computing platforms and larger embedded systems rather than a Small Embedded System.

 

However the concept behind them support rapid prototyping and minimal code writing to get to a working demonstration. Rapid Application Development is primarily about doing this. Get to a prototype fast then find out what the problems are. You can think of this as Risk Identification. Identifying and eliminating risks early is one of our core strategies for delivering projects on time and budget and is covered in more detail in our Project Management Methodology.

 

Modelling

Another common approach is the Unified Modelling Language or UML. This uses an open standard for a visual model to drive the code generation. You get the model right and the tool produces the Embedded C code for you. This is also important for reusability. The models are processor independent so in theory you can use them on any processor the toolset supports. They support state based design most easily but can be hard work for highly algorithmic processes or communications processing engines.

 

Regardless of the Software Design Methodology selected, the coding must still be done with care. But selecting the right Software Design approach makes that a much more likely process.

 

Successful Endeavours specialise in Electronics Design and Embedded Software Development. Ray Keefe has developed market leading electronics products in Australia for nearly 30 years. This post is Copyright © 2012 Successful Endeavours Pty Ltd

Embedded Software Testing

Software Testing

I recently met with an Australian Software Development company, PepperStack, and we got onto the subject of Software Testing. As someone who began their career as an Electronics Hardware Engineer, one of the things I learnt was that you have to test thoroughly to be sure everything is working as it should be. With Electronics, if you make a mistake with an Engineering Calculation you can easily destroy things. This is sometimes referred to as “letting the smoke out”. So it was good to meet with others who believe in the same level of rigorous software unit, module and system testing that we do.

 

 

Some Engineering Humour

Which reminds me of a joke I once heard:

 

There are 3 Engineers in a car going for a drive. The first is a Mechanical Engineer, the second an Electronics Engineer and the third is a Software Engineer. Fortunately the Mechanical Engineer is driving because the brakes fail and they are going downhill. The Mechanical Engineer eventually brings the car safely to a halt and gets out to examine the hydraulic systems. The Electronics Engineer gets out and checks and body computer, ABS system and the power train CAN bus. The Software Engineer stays in the car and when queried about it says that they should all just get back in the car and see if it happens again!

 

Now don’t get me wrong, I’m not having a go at Software Engineers. The process of finding and eliminating faults is a very important part of the development cycle and is something that needs up front thinking and not just responding to symptoms. And the more complex or sophisticated a system is, that harder it is to fully test every possible response to every possible stimuli and after a certain point it becomes impractical to have 100% Test Coverage (every line of code has been executed through all of the possible states). The reason this is a bigger problem with Software Development is that the flexibility of software means that it is inherently complex and it takes skill and planning to manage that complexity so it is testable.

 

So here is the issue. More than any other discipline, faults can be experienced by an end user of a product under a situation or scenario you could not have proactively tested against before release. There are many potential reasons for this including:

  • change of hardware or operating system environment
  • new standards or protocols
  • the sheer number of potential combinations of drivers, peripherals, software and users
  • the product being used for a purpose it wasn’t originally designed for
  • gamma ray corruption of a memory location – I am getting esoteric now but in some areas like avionics and space this is a big threat

So how do you reduce the likelihood of these problems occurring?

 

 

Improving Software Quality

With many new products having Electronics and Embedded Software and the Software Development requiring 80% of the effort, it is important to delivery it as quickly and fault free as you can. The main weapons in your Software Quality arsenal have been known about for a long time but are, in our experience, just not used. These are:

  • Architectural Design – work out how the data and execution flow will happen and how you will manage the constraints
  • Functional Decomposition – divide and conquer but with an emphasis on how each module fits into the system and how the interfaces work in detail
  • Error handling – who will decide what to do with response codes – again this is data and execution flow and part of the architecture. In many cases exception management is at least 50% of the project.
  • Have an Integration Test Plan – some thing that proves the data and execution flow matches the architectural design. Too often “it builds” seems to be good enough here.
  • Unit Test modules – so you remove all the issues before adding them to the integration
  • Do the Integration Tests before you try system testing
  • Design modules so you can integrate them as shells then add functionality down the track
  • Have NVM and configuration data available at the beginning of the project and not as an after thought at the end
  • Have a System Test Plan and use it
  • Use some of the good practices of Test Driven Development – run the tests every time you change the code
  • Have a rationale for what level of Code Coverage you can accept
  • Have a rationale for what level of Churn you can accept – Churn is the percentage of the lines of code that have changed in the past time period. Usually either a week or month depending on the size of the project.
  • Use automated software quality tools. For instance we use both PC-Lint and RSM to automated many software quality metrics which saves a lot of time in Code Reviews
  • Use Code Reviews, also known as Software Peer Review. It really does save time.

Next I plan to look at what you can learn about software testing from a Squash Racquet.

 

Ray Keefe has been developing high quality and market leading electronics products in Australia for nearly 30 years. For more information go to his LinkedIn profile. This post is Copyright © 2010 Successful Endeavours Pty Ltd.

Improving Product Development Outcomes

In this post we will look at the Product Development Process and how to get improved outcomes. But first here is a fun graphic made from our logo.

Successful Endeavours - Making Electronics and Embedded Software Work

Successful Endeavours – Making Electronics and Embedded Software Work

Product Development Process

The Product Development Process is intended to reliably deliver new products for manufacture or distribution. This is a critical component of a Product Strategy where you are creating the product rather than sourcing it from a supplier. So you would think that it should be a highly optimised, well oiled machine that reliably delivers successful products. Alas that is not always the case. With 30 years of experience in Developing Products for a wide range of industries I have seen my share of projects handled well and not so well. Here are some general principles I have gleaned from my experience in Successful Product Development Projects:

  • Risks must be identified and managed. Track them and eliminate them as soon as possible.
  • Anything clever or tricky needs to be checked by someone else.
  • Everything else also gets checked. Design reviews, code walk-throughs and prototypes save time, money and heart ache later on.
  • Hold the timeline. Foster an attitude that slippage is not acceptable.
  • Test and check everything.
  • It’s not finished until no-one has to do another thing to it.

So six core principles. They are inter related of cousre. Let’s look at how these work out in practice.

 

Successful Product Development Principles

Lets look at how each of these priciples can be used to improve the likelihood of a Successful Product Development Project.

Risk ManagementRiskManagement

Risk Management is an old idea. Not surprising since risks have always existed. Did you know that during the Manhattan Project it was determined that there was a chance that a fission bomb could ignite the whole atmosphere ? Having got contradictory reports the argument was eventually settled by a report showing that although it was possible, it was unlikely. How comfortable would you feel running that risk ? Fortunately the average Development Project is dealing with much more mundane risks such as achieving Technical Requirements such as:

  • Power Consumption
  • Unit Manufacturing Cost
  • Performance Criteria

But the approach is still the same:

  • Identify the risk
  • Work out how to ameliorate the risk – reduce it – or eliminate it
  • Do tests to confirm the risk has been dealt with
  • Iterate until it is no longer a risk

Review the clever bits

Test Everything - Clever Design Needs Test

Test Everything – Clever Design Needs Test

Where possible, any particularly clever or tricky areas of the project need to be reviewed by someone not involved in the everyday work of the project. This is primarily to ensure that assumptions are challenged. If you can’t get an outsider to do the review, use a process like Six Thinking Hats by Edward De Bono which can allow team members to step outside their emotional and assumptive predispositions. Unchallenged assumptions are unmanaged risks.

 

Review the rest of the project

Test Everything

Review Everything

The astute amongst would have noticed that I am proposing everything gets reviewed. But the tricky bits get extra review. This section is for the regular bits. Reviews are an essential tool to find mistakes early and eliminate problems down the track. You don’t have to solve a problem you don’t have. Or as Jack Ganssle famously quipped “Skip Bugging To Speed Delivery“. The whole article refers to using Code Review and Design Review to find problems early and fix them so they don’t become much bigger problems later on. Imagine a scenario where a Software Bug causes an electric motor to try and spin backward every now and again and then corrected itself almost immediately. You would get a momentary shudder or jerk followed by correct motion and it would only happen every now and again. How would you determine that this was a software fault and where the fault lay? It could be symptomatic of any number of issues including Mechanical Design and Electrical Design. How about this similar real world case. I won’t mention the company, but their elevators had an Integer Overflow problem in the motor controller that caused the elevator to go in the wrong direction, about once a month, for half a floor. Very disconcerting to the passengers if they pressed up, and promptly dropped half a floor before then going up. Fortunately they found it and fixed it before it happened to someone at the top or bottom floor. All the Software Industry Metrics show for that for Software Development; Design Review, Code Review, Unit Tests and System Simulation save money and time. And yet in many projects they don’t happen enough or are done after the event as a Quality Assurance box ticking activity where they add mostly cost and little in the way of value. Lean Coding argues that you can reduce your Software Development Budget in particular by doing Code Inspections during the project as part of the Risk Management and Quality Management process. By reducing the bugging, you can reduce the debugging.

 

Stick to the Timeline

Project Development Timeline

Project Development Timeline

An attitude that the schedule slipping is normal can be very costly. Some examples of how to avoid this are:

  • Develop and Simulate the Software before the Hardware is ready
  • Prototype early and thoroughly
  • buy in IP where it makes financial sense – this can also reduce risk
  • get expert assistance with areas outside your competence
  • review regularly and honestly

As someone who has done a lot of team leading and project management, I have learned to ask about progress in more than one way. I find the following to be very common: Manager: “This module is estimated as 10 days of work to complete. How complete is it”? Developer: “About 80%”. Manager: “How many more days of work are required to fully finish everything”? Developer: “To fully finish everything, I would think 6 more days would cover it all”. The discrepancy is easy to spot. People estimate high on progress because they want to please. They also like to finish well so they tend to estimate conservatively on required effort. In practice the real answer lies somewhere between the 2 extremes. If the task had already consumed 6 days of effort then it is likely to run late. If you have ever built a house you might have experienced the knock on effect it has when one trades person doesn’t turn up and everyone else misses their scheduled action time because they are now waiting on a predecessor task, the trades person who has to come back again, before they can start their task. The same thing happens on projects. So fight hard to hold to the schedule. It is better to over resource a task (according to the plan) and get it done than to let everything and everyone slip which usually costs a lot more. Additionally, it is quite common that the later you are in the market, the lower the overall profit. So it is worth holding the schedule for this reason as well.

 

Test and Check Everything

Test Everything

Test Everything

This is another Risk Management related principle. Don’t assume it will be OK. Even if you have done it 100 times before, test it again this time. Make sure it really is OK. This ensures it really is 100% complete. This also implies that you are going to design things so they can be tested. Another principle. Design For Testability or somestimes called Design For Test. Do it. It will save you time, effort, money and sleep. Test Driven Development is another example of a Modern Development Methodology where you set up the test first then develop the product so it passes the test. If the Product Requirements change, you change the tests first, show that the old Product Design fails the test, then update the Product Design until it now passes the test.

 

It is not finished until no-one has to do anything else to it

Many tasks are called complete but they aren’t. The documents might be checked into the Revision Control System, also known as a Version Control System or Version Management System, but it isn’t complete until it is 100% tested, 100% integrated, 100% reviewed and 100% signed off and no-one has to do another thing. This also means that when tasks are identified that weren’t thought of in the original Project Plan, you then add them and don’t try and fiddle them into existing tasks. This is different to working out the fine detail of a task and realising it is under resourced or over resourced on the Project Plan. You also want the extra tasks visible on the Project Management Plan so when you do the next project you have evidence that they were required last time and can make allowances for them.

 

Trip Assurance for Developers

Satisfaction Guaranteed

Satisfaction Guaranteed

In marketing, the term Trip Assurance refers to the client having a clear expectation of this transaction or experience being a good one, just like every other one has been. I think we can begin to develop some of the same as developers whereby projects can be routinely good experiences and likely to be so each time.

 

This post is also available as an eZine article with Expert Author classification.

 

Ray Keefe has been developing high quality and market leading electronics products in Australia for nearly 30 years. For more information go to his LinkedIn profile. This post is Copyright © Successful Endeavours Pty Ltd.