File content as of revision 1:f6715f1bf6a6:

#include "mbed.h"

/*------------ Constant definitions --------------*/
#define TX_PIN          USBTX
#define RX_PIN          USBRX
#define BRATE           115200
#define LED_PIN         LED0
#define TOGGLE_RATE     (0.5f)
#define BUFF_LENGTH     5

/*-------- Check if platform compatible ----------*/
#if DEVICE_SERIAL_ASYNCH
Serial test_connection(USBTX, USBRX);
#else
#error "Platform not compatible with Low Power APIs for Serial"
#endif

/*------------------ Variables -------------------*/
LowPowerTicker      blinker;
bool                blinking = false;
event_callback_t    serialEventCb;
DigitalOut          LED;
char                rx_buf[BUFF_LENGTH + 1];

/*------------------ Callbacks -------------------*/
void blink(void) {
    LED = ~LED;
}

void serialCb(int events) {
    /* Something triggered the callback, either buffer is full or 'S' is received */
    unsigned char i = 0;
    if(events & SERIAL_EVENT_RX_CHARACTER_MATCH) {
        //Received 'S', check for buffer length
        for(unsigned char i; i < BUFF_LENGTH; i++) {
            //Found the length!
            if(rx_buf[i] == 'S') break;
        }
        
        // Toggle blinking
        if(blinking) {
            blinker.detach();
            blinking = false;
        } else {
            blinker.attach(blink, TOGGLE_RATE);
            blinking = true;
        }
    } else if (events & SERIAL_EVENT_RX_COMPLETE) {
        i = BUFF_LENGTH - 1;
    } else {
        rx_buf[0] = 'E';
        rx_buf[1] = 'R';
        rx_buf[2] = 'R';
        rx_buf[3] = '!';
        rx_buf[4] = 0;
        i = 3;
    }
    
    // Echo string, no callback
    test_connection.write(rx_buf, i+1, (event_callback_t*)0, 0);
    
    // Reset serial reception
    test_connection.read(rx_buf, BUFF_LENGTH, &serialEventCb, SERIAL_EVENT_RX_ALL, 'S');
}

/*-------------------- Main ----------------------*/
int main() {
    /* Very Simple Main (tm) */
    serialEventCb.attach(serialCb);
    
    /* Setup serial connection */
    test_connection.baud(BRATE);
    test_connection.printf("Low Power API test\n\nSend 'S' to toggle blinking\n");
    test_connection.read(rx_buf, BUFF_LENGTH, &serialEventCb, SERIAL_EVENT_RX_ALL, 'S');
    
    /* Let the callbacks take care of everything */
    while(1) sleep();
}