int decodeS72xx(unsigned char* data, int len) {
unsigned char c = 0xaa;
unsigned char p0=0;
unsigned char p1=0;
for(int i=0; i<len; i++) {
unsigned char x = data[i];
if(i%2) {
data[i]^=(p0^c);
p0 = x;
} else {
data[i]^=(p1^c);
p1 = x;
}
}
return 0;
}