Software Problems with a Breath Alcohol Detector

[Swede]

2. Readings are Not Averaged Correctly: When the software takes a series of readings, it first averages the first two readings. Then, it averages the third reading with the average just computed. Then the fourth reading is averaged with the new average, and so on. There is no comment or note detailing a reason for this calculation, which would cause the first reading to have more weight than successive readings. Nonetheless, the comments say that the values should be averaged, and they are not.
3. Results Limited to Small, Discrete Values: The A/D converters measuring the IR readings and the fuel cell readings can produce values between 0 and 4095. However, the software divides the final average(s) by 256, meaning the final result can only have 16 values to represent the five-volt range (or less), or, represent the range of alcohol readings possible. This is a loss of precision in the data; of a possible twelve bits of information, only four bits are used. Further, because of an attribute in the IR calculations, the result value is further divided in half. This means that only 8 values are possible for the IR detection, and this is compared against the 16 values of the fuel cell.

4. Catastrophic Error Detection Is Disabled: An interrupt that detects that the microprocessor is trying to execute an illegal instruction is disabled, meaning that the Alcotest software could appear to run correctly while executing wild branches or invalid code for a period of time. Other interrupts ignored are the Computer Operating Property (a watchdog timer), and the Software Interrupt.


Basically, the system was designed to return some sort of result regardless.

http://www.schneier.com/blog/archives/2009/05/software_proble.html

[MineralMan]

1. On Error Resume Next

While this sort of error handling can be useful in some circumstances, it's poor programming practice when it is used to simply bypass calculation errors.

[kickysnana]

2. On the memories mid 1980's

Network Systems is rolling out its first PC to PC networking units. I was hired as a board technician but they laid off quality control and had us doing pretests on boards manufactured elsewhere for assembly. We had about 50% failures. They changed the testing software and suddenly everything passed. I didn't buy it and figured we would get blamed. The old test was still installed so I ran two batches different shipments. The next week during a lull I retested boards and found that the older ones still had 50% failure but the newest ones had 100% failure. I alerted my supervisor who called in the engineers and we were told to go back to the old tests but it sealed my fate at the company.

The product rolled out January 1st. The week before I was laid off three months later the field techs reported that they had not had one unit actually operating in the field yet. I assumed it was difficult to sell them at that point.

[endless october]

3. if authorities really wanted to lower occurance of DUI...

they would make damned sure there was an AFFORDABLE, ACCURATE breathalyzer available for 25 bucks in every Walmart.

seriously, why don't we attack the problem that way? i'd buy one. wouldn't you?

[Swede]

4. Sounds good to me.