[ECOS] nc_test_slave.c fix

[Hugo 'NOx' Tyson]

I had to fiddle with this further for a paricularly fast platform.

The previous version from Grant (thanks Dude!) starts with a high bound and
a low bound and binary chops its way to the correct answer.

But if the high bound is not high enough, it stops *without placing enough
load on the machine*.

The solution is an initial doubling loop that scales up the high load (and
coincidentally replaces the low load with a higher, but known low load) if
that's necessary to bracket the desired load.  That loop will execute once
and make no change to the params if the initial high is indeed high enough.

It also features a post scaling to get that last leetle bit closer; for
example, if our measured load is 52% and we want 50%, 50*load/52 has to be
a better estimate.  And it is.

Here's the new calibrate_load() routine.

	- Huge

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static void
calibrate_load(int desired_load)
{
    long long no_load_idle, load_idle;
    int percent_load;
    int high, low;

    // Set limits
    high = MAX_LOAD_THREAD_LEVEL;
    low = MIN_LOAD_THREAD_LEVEL;

    // Compute the "no load" idle value
    idle_thread_count = 0;
    cyg_semaphore_post(&idle_thread_sem);  // Start idle thread
    cyg_thread_delay(1*100);               // Pause for one second
    cyg_semaphore_wait(&idle_thread_sem);  // Stop idle thread
    no_load_idle = idle_thread_count;
    diag_printf("No load = %d\n", (int)idle_thread_count);

    // First ensure that the HIGH level is indeed higher
    while (true) {
        load_thread_level = high;
        start_load(desired_load);              // Start up a given load
        idle_thread_count = 0;
        cyg_semaphore_post(&idle_thread_sem);  // Start idle thread
        cyg_thread_delay(1*100);               // Pause for one second
        cyg_semaphore_wait(&idle_thread_sem);  // Stop idle thread
        load_idle = idle_thread_count;
        start_load(0);                         // Shut down background load
        percent_load = 100 - ((load_idle * 100) / no_load_idle);
        diag_printf("High Load[%d] = %d => %d%%\n", load_thread_level, 
                    (int)idle_thread_count, percent_load);
        if ( percent_load > desired_load )
            break; // HIGH level is indeed higher
        low = load_thread_level; // known to be lower
        high *= 2; // else double it and try again
    }

    // Now chop down to the level required
    while (true) {
        load_thread_level = (high + low) / 2;
        start_load(desired_load);              // Start up a given load
        idle_thread_count = 0;
        cyg_semaphore_post(&idle_thread_sem);  // Start idle thread
        cyg_thread_delay(1*100);               // Pause for one second
        cyg_semaphore_wait(&idle_thread_sem);  // Stop idle thread
        load_idle = idle_thread_count;
        start_load(0);                         // Shut down background load
        percent_load = 100 - ((load_idle * 100) / no_load_idle);
        diag_printf("Load[%d] = %d => %d%%\n", load_thread_level, 
                    (int)idle_thread_count, percent_load);
        if (((high-low) <= 1) || (abs(desired_load-percent_load) <= 2)) break;
        if (percent_load < desired_load) {
            low = load_thread_level;
        } else {            
            high = load_thread_level;
        }
    }

    // Now we are within a few percent of the target; scale the load
    // factor to get a better fit, and test it, print the answer.
    load_thread_level *= desired_load;
    load_thread_level /= percent_load;
    start_load(desired_load);              // Start up a given load
    idle_thread_count = 0;
    cyg_semaphore_post(&idle_thread_sem);  // Start idle thread
    cyg_thread_delay(1*100);               // Pause for one second
    cyg_semaphore_wait(&idle_thread_sem);  // Stop idle thread
    load_idle = idle_thread_count;
    start_load(0);                         // Shut down background load
    percent_load = 100 - ((load_idle * 100) / no_load_idle);
    diag_printf("Final load[%d] = %d => %d%%\n", load_thread_level, 
                (int)idle_thread_count, percent_load);
//    no_load_idle_count_1_second = no_load_idle;
}

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