PTR_READ
smc_write_2(sc, PTR, 0 | PTR_READ | PTR_RCV | PTR_AUTO_INCR);
smc_write_2(sc, PTR, 4 | PTR_READ | PTR_RCV | PTR_AUTO_INCR);
smc_write_2(sc, PTR, 0 | PTR_READ |