File content as of revision 1:cedd9360f5c7:

#include "mbed.h"

//Init Pins
SPI spi(D11, D12, D13);
DigitalOut cs(D10, 1);

void init() {
    cs = 0;
 
    spi.write(0x46); // Select IODIR
    spi.write(0x00); // 0000 = Set all to output
    spi.write(0x00);
  
    // Deselect the device
    cs = 1;
}

void setLed(int i) {
    cs = 0;
    spi.write(0x46);
    spi.write(0x09);
    
    int mask = 1;
    int writeValue = 255;
    writeValue ^= mask << i;
    spi.write(writeValue);
    cs = 1;
}

int readButton() {
    cs = 0;
    spi.write(0x47);
    spi.write(0x09);
    int misoOutput = spi.write(0x00);
    cs = 1;
    
    misoOutput = misoOutput & 192;
    printf("output miso: %d", misoOutput);
    if (misoOutput == 128) { // S1 pressed
        return 1;    
    } else if (misoOutput == 64) { // S2 pressed
        return 5;
    }
    return 0;
}

int main() {    
    cs = 1;
    printf("Initializing. \n\r");
    init();
    printf("Setting Led. \n\r");
    
    // Select the device by seting chip select low
    int led = 0;
    printf("Starting \n\r");
    while (true) {
        setLed(led);
        led = (led + readButton()) % 6;
        wait(0.1);
    }
}