pedestrian road crossing - c code

I do ralize that the code is very poorly written, however it is written for self educational purposes only.

You have that dangerously backwards. Knowingly writing poor code may sometimes be justified by pressing circumstances (e.g. momentary lack of time to do it right), but never in a setting of self-education.

If you can't do it properly with practically infinite amounts of time on your hands, how will you ever do an acceptable job under stress?

I do ralize that the code is very poorly written, however it is written for self educational purposes only.

You have that dangerously backwards. Knowingly writing poor code may sometimes be justified by pressing circumstances (e.g. momentary lack of time to do it right), but never in a setting of self-education.

If you can't do it properly with practically infinite amounts of time on your hands, how will you ever do an acceptable job under stress?

I do not work in a programming business and most probably never will. As far as my area of expertise is concerned I do think that I do more than an acceptable job under stress.

Thanks for your help guys.
I have learned a great deal about philosophical issues in programming. Unfortunately I did not learn that much about actual coding itself. Consider the matter ad acta.
Thanks again!
Best regards,
Marko

Unfortunately I did not learn that much about actual coding itself.

But you did learn (or at least should have learned) quite a lot from this thread.

Delays generated using a compiler (might be a C, Pascal or whatever compiler) does give the possibility of unexpected changes to the delay time.

Optimization of loops may sometime result in the loop being completely removed - a compiler that doesn't notice any side effect are free to ignore the meaningless code.

It is possible to generate longer delays, by generating delays of known length and call that delay from a loop.

Using numeric constants larger than supported can give results that may look non-obvious.

The recommended method for creating delays are using timers (unless the delay should be extremely short, in which case you normally just add one or more NOP statements in assembler).

Goto isn't forbidden, but shuld normally not be used for implementing state machines or loops. Their best - and possibly only - suggested use is to break out of multiple loops.

Using tabs to indent source, results in slightly smaller source files, but the amount of indentation can't be guaranteed.

Mixing spaces and tabs when indenting generates code that may look really funny (or not) when displayed with a different tab size.

Setting breakpoints - or single-stepping - the code in the simulator would have shown problems with the delay functions.

Some compilers generates warnings that are important to look at. Some compilers do not generate so many warnings, so you can't always rely on warnings/errors to catch all possible errirs in the source.

You got some references to literature.

I problably missed some things in the thread, but philosophy aside: There was definitely a lot to learn about programming in this thread.

Unfortunately I did not learn that much about actual coding itself.

That makes me want to sit down and cry.

Why did you not learn anything about coding ?

The first problem your code runs into was described in great detail.

Ways to tackle the next problems you're going to run into were described in good detail.

Good coding practices were described (I'm sorry if you mistook them for philosophical issues. Once you've been trying to unravel a sparsely commented, goto-infested hunk of spaghetti code, you are going to realize that good coding practices are essential in everyday programming and not an abstract matter of philosophy.).

Ah, here's another one: Comments ! Uncommented source code is worthless. Everyone (including yourself) will have a hard time understanding what the code is supposed to do without comments. If you don't have a clear perception of what the code is supposed to do, it becomes very hard (close to impossible) to find out where and why the code is not doing what it is supposed to do.

Don't play the macho tough guy programmer who can memorize every tiny bit of information about his programs and keep that memory for months or years. Chances are, you can't (like most others programmers). Even if you can, you're going to make the life of any other programmer you deal with (that includes those you ask to look at your source code and give you hints) miserable.

Good commenting practices are even more important than having ultra-elite coding skills. Once you've got the comments down (yes, write them first), generating the appropriate code is a fairly simple matter (where most problems can be solved by just consulting a textbook).

Uncommented source code

there is no such thing, if there are no comments, it is not code, it is scribbles

Erik

One way to increase your delay is to add NOPs (the asm code for No Operation Keil gives you a macro for it

void delay(unsigned int msec)
{
    unsigned int x;

    while (msec > 0)
    {
       // YOU Need to figure out the number of nops
       // and how big x needs to be
       // since x is an unsigned int it must be less than 65535
       for (x=0;x<9999;x++)
       {
          _nop_;
          _nop_;
          _nop_;
          _nop_;
          _nop_;
       }
       msec--;
   }

 }

 the time a nop uses is different  for different cpus
The standard is 1/12 the crystal frequency.

This will get you started.  You would move on to using the timer interupt later.
the interupt also give you the benifit that your cpu is not doing nothing during the delays.  It can do something else during the delay time.

1."Goto" statement has been replaced with while.
2.Delays are generated by using 8051's internal timer.
3.The code is now hopefully properly commented.

What I would like to do now is to extend the whole thing a bit by adding a sort of a lock-out function for the pedestrian button so that green pedestrian light cannot go green too quickly since the last time the button was pressed because that would hinder the flow of traffic.
I do have a general idea of how to do that using a counter/timer, but implementation is a bit tricky for me because of my lack of skills.
The code should probably look something like this:
1.when a button is pressed a counter should be started
2.if a button is pressed again the counter should be checked to see if it has reached a certain level
3.if the level has been reached the program should continue
4.if the level has not been reached the counter should continue counting till the level is reached
6.when the level is reached stop the counter and continue with the program

Would that be a good approach?
Any comments regarding the code?

Regards,
Marko

P.S.
The code so far:

#include <reg664.h>    //register map for 8051

#define ON      1
#define OFF     0

sbit red_traf = P1^0;   //red traffic light is connected to bit 0 of P1
sbit amber_traf = P1^1; //amber traffic light is connected to bit 1 of P1
sbit green_traf = P1^2; //green traffic light is connected to bit 2 of P1
sbit red_ped = P1^3;    //red pedestrian light is connected to bit 3 of P1
sbit green_ped = P1^4;  //green pedestrian light is connected to bit 4 of P1
sbit bleeper = P1^5;    //bleeper is connected to bit 5 of P1
sbit button = P2^0;     //pedestrian button is connected to bit 0 of P2
unsigned char count;

void delay(int del)                     //delay procedure
        {
        int c=0;
        TMOD=0x01;                      //CT1 not used, CT0 as a timer, in mode 01
        TR0=0;
        TF0=0;
                do
                {
                TH0=0;                  //Load CT0 with zero to get
                TL0=0;                  //the longest possible time.
                TR0=1;                  //start timer
                while(!TF0);            //while Timer Flag is low, do nothing i.e.wait till it goes high
                TR0=0;                  //stop timer
                TF0=0;                  //make timer flag low again
                c++;
                }
        while (c<del);
        }

main()
{
        while (1)                       //infinite loop

        {
            P1 = 0x00;                 //reset all bits of P1
            P2 = 0xff;                 //Make all bits 1, so that port2 works as
                                       //an input port.

            /* Go traffic */
            // traffic:     G = ON,  A = OFF, R = OFF

            // pedestrians: G = OFF,          R = ON

            green_traf = ON;
            red_ped    = ON;

            while (button) {}         // wait for button

            // traffic:     G = OFF, A = ON,  R = OFF

            // pedestrians: G = OFF,          R = ON  - no change

            green_traf = OFF;
            amber_traf = ON;

            delay (30);              // short delay


            /* Go pedestrians */
            // traffic:     G = OFF, A = OFF, R = ON

            // pedestrians: G = ON,           R = OFF

            amber_traf = OFF;
                red_traf  = ON;
            red_ped   = OFF;
            green_ped = ON;

            bleeper   = ON;     // turn bleeper on

                delay (100);    // long delay

            // traffic:     G = OFF, A = ON, R = OFF

            // pedestrians: G = ON,          R = OFF

            bleeper = OFF;      //Turn off the bleeper
            red_traf=OFF;       //Switch off red traffic light

            for (count=0;count<7;count++)   //This will make amber traffic and green pedestrian light flash five times
                {
                amber_traf=ON;          //Switch amber traffic light on
                green_ped=ON;           //Switch green pedestrian light on
                delay(5);               //Wait for a very short time
                amber_traf=OFF;         //Switch both previous lights off
                green_ped=OFF;
                delay(5);
                }
        }               //infinite loop
}                       //main

Neil Kurzman thanks for your comments. They were very useful.

Regards,
Marko

Think a bit more about your comments.

Make sure that your functions and variables have names so that you never have to make comments about what you do.

You seldom want to write comments that say _what_ you do - unless you have a very hairy algorithm. You normally want to write comments about _why_ you do things.

Why use comment "turn off bleeper" for a line like:

bleeper = OFF;

Why comment delay(100) as "long delay"? How long is it? Why do you have a delay? If the delay function makes delays in ms - rename it as delay_ms(delay) and let the reader decide if it is a long delay or not.

Now you are programming. You need a plan.
One way to do this is to have a periodic "Event" either in an interupt if it is short. Else, the interupt sets a flag and the event is handled from a function call in main.

Lets assume you set a flag every 100ms in an interupt.

when this flag is seen in the main loop you can decrement all your timers by 1 tick.

Example
if(tickFlag)
{
   tickFlag = 0;              // clear tick flag
   if(Counter1 > 0)Counter1--;// dec counter down to 0
}

Then assuming Counter1 was you timer lock out. You would ignore the button if the counter is not 0;

This is one posible way. There are may ways to do this task.