File content as of revision 0:de199215b4c0:

#include "mbed.h"

DigitalOut myled(LED1);
Serial pc(USBTX, USBRX);

// (GS1011MxxS / pin)
SPI gs(p5, p6, p7); // mosi(DIN/5), miso(DOUT/8), sck(CLK/7)
DigitalOut cs(p8); // cs(CS/6)
DigitalIn hw(p9); // host wakeup(GPIO28/2)

int main() {
    char c;

    pc.baud(115200);
    gs.format(8, 0);
    gs.frequency(3000000);
    hw.mode(PullDown);
    myled = 1;
    cs = 1;

    for (;;) {
        if (pc.readable()) {
            cs = 0;
            c = gs.write(pc.getc());
            if (c != 0xf5)
                pc.printf("%02x_", c);
            cs = 1;
        }
        if (hw == 1) {
            cs = 0;
            c = gs.write(0xf5);
            cs = 1;
            if ((c >= 0x20 && c < 0x7f) || c == 0x0d || c == 0x0a) {
                pc.printf("%c", c);
            } else
            if (c != 0xf5) {
                pc.printf("%02x ", c);
            }
        }
    }
}