ATARI_CKS_LOC
return (__nvram_read_byte(ATARI_CKS_LOC) == (~sum & 0xff)) &&
(__nvram_read_byte(ATARI_CKS_LOC + 1) == (sum & 0xff));
__nvram_write_byte(~sum, ATARI_CKS_LOC);
__nvram_write_byte(sum, ATARI_CKS_LOC + 1);