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long int random(void)
This function returns a pseudorandom number.
void srandom(unsigned int seed)
Use this function to provide a new seed for the pseudorandom number generator.
Page 204
In string.h
There are also functions for working with text strings:
char
∗
strcpy(char
∗
dest, const char
∗
src)
int strlen(const char
∗
s)
int strcmp(const char
∗
s1, const char
∗
s2)
These are the standard string copy, length, and compare functions.
In time.h
You can retrieve the number of milliseconds since the RCX was powered up using the
sys_time
variable. It's got a limited range; the count resets once every 49.7 days.
In rom/system.h
Your programs have tremendous power in legOS. You can turn the RCX off or even obliterate legOS and your program from memory, using these functions:
void power_off(void)
This function puts the RCX into its low power consumption "off" mode.
void rom_reset(void)
This functions resets the RCX to its out-of-the-box state, essentially blowing away legOS and your program. This is really only useful if you want to load some new firmware on the RCX. Use
with care!
New Brains for Hank
In this section I'll present a longer example program. It's a program for a slightly modified version of Hank, the robot from Chapter 2, Hank, the Bumper Tank. All you need to do is mount the light
sensor on the front of Hank and attach it to input 2. This light sensor will allow Hank to search for light, while the bumpers allow him to avoid obstacles. Figure 10-2 shows a picture of Hank,
newly fitted with the light sensor.
Hank's new legOS program will be implemented using subsumption architecture. The basic structure of the program is similar to the subsumption architecture example presented in Chapter 9,
RoboTag, a Game for Two Robots, although the syntax is somewhat different.
Hank's light-seeking proclivity is produced by the interaction of three behaviors:
• cruise , as in the RoboTag program, constantly tries to move forward.
•
seek_enlightenment()
examines the values of the light sensor. If the values are decreasing, generally speaking, this behavior attempts to turn Hank back toward the light.