Programming Embedded Systems in C and C++

Das Blinkenlights 15

limited to a few lines of C or assembly, so there is very little room for program-

ming errors to occur. And because almost all embedded systems have LEDs, the

underlying concept is extremely portable.

The superstructure of the Blinking LED program is shown below. This part of the

program is hardware-independent. However, it relies on the hardware-dependent

functions toggleLed and delay to change the state of the LED and handle the tim-

ing, respectively.

/**********************************************************************

*

* Function: main()

*

* Description: Blink the green LED once a second.

*

* Notes: This outer loop is hardware-independent. However,

* it depends on two hardware-dependent functions.

*

* Returns: This routine contains an infinite loop.

*

**********************************************************************/

void

main(void)

{

while (1)

{

toggleLed(LED_GREEN); /* Change the state of the LED. */

delay(500); /* Pause for 500 milliseconds. */

}

} /* main() */

toggleLed

In the case of the Arcom board, there are actually two LEDs: one red and one

green. The state of each LED is controlled by a bit in a register called the Port 2

I/O Latch Register (P2LTCH, for short). This register is located within the very

same chip as the CPU and takes its name from the fact that it contains the latched

state of eight I/O pins found on the exterior of that chip. Collectively, ...