Al Hoang

This is OK for a simple algorithm, but what if it is even moderately complex?

Then you are dealing with (i) a very complex algorithm and (ii) very complex

assembler all at the same time. This is usually too much for mere mortals (and

even minor deities). The result is long, painful development, failed projects,

late nights, angry spouses, and lots of pizza (well its not all bad I guess).

The trick is to divide and conquer. Make sure we are only hitting one tough

problem at any given time.

One approach I have found very useful is bit

exact porting to assembler.

There are two important steps:

1. At the fixed point C stage, you test very very carefully. Run batteries

   of tests and simulations. These can be performed on a regular PC in non real

   time, using powerful debuggers. The idea is to verify that:

   (i) The algorithm is OK and

   (ii) The fixed point port works OK.

   In particular (ii) is very tough, so its nice to handle this in a relatively

   benign environment like a PC or

   workstation.

2. Port each function to real time assembler one by one. Test each function

   against the fixed point C reference. Make sure the functions give IDENTICAL

   output – right down to the last bit. This takes a lot of discipline – near

   enough is NOT good enough.

First, let’s touch on requirements gathering. No where in the book did Pressman

illustrate how most engineers actually get their requirements. He presented

some idealized scenarios, and correctly illustrated the benefits of use cases.

But in the real world, most requirements come from emails and rough wireframes.

Assuming that we can start by writing the specification is folly. What we

should be studying is how to turn a screen shot created in Photoshop in to a

real specification. Engineers need to learn how to annotate a screen shot with

input validation rules. They also need to error messages and edge cases. And

they need to do it with the understanding that their stakeholders don’t know or

care about such matters unless you bring it up to them first.