C2N
cksum -= (C2N(c) << 4) & 0xf0;
cksum -= C2N(c) & 0x0f;
c = (C2N(gdb_rxp[0]) << 4) & 0xf0;
c |= C2N(gdb_rxp[1]) & 0x0f;
v += C2N(c);