Page 209 - The Unofficial Guide to Lego Mindstorms Robots

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The rotation sensor code does not work in the March 30, 1999 build of legOS 0.1.7

Using the Buttons (d irect-button.h)

le gOS provides one function and some other handy defi nitions to describe the state of the front panel buttons:

in t button_state(void)
This function returns a value that in dicates the state of the RCX's four buttons. Use the following macros to interpret the
returned value.

PRESSED(state, button)

R ELEASED(state, button)

These macros return a boolean value indicating if the specified button was pressed or not. To use these macros, pass the
result of button_state() as the state parameter and the name of a button for button. Buttons names are
BUTTON_ONOFF, BUTTON_RUN, BUTTON_VIEW, and BUTTON_PROGRAM.

For example, the following code tests the state of the View button:

if (PRESSED(button_st ate(), BUTTON_VIEW)) {
// View button is pressed.
}

To test the state of more than one button, it makes sense to store the result of button_state(), like this:

int state;
state = button_state();
if (PRESSED (state, BUTTON_VIEW)) {
// View button is pressed.
}
if (PRESSED(state, BUTTON_PROGRAM) ) {
// Program but ton is pressed.
}

The fr ared Port (direct-ir.h)
n
I

To send data out the IR port, ju st use the dir_write() func tion:

size_t dir_write(void∗ const buf, size_t len)

This func tion writes len bytes of data from the supplied buffer out the IR port. It returns the number of bytes written or -1 if
there is an error.