__nvram_write_byte
__nvram_write_byte(*p, i);
__nvram_write_byte(~sum, ATARI_CKS_LOC);
__nvram_write_byte(sum, ATARI_CKS_LOC + 1);
__nvram_write_byte(0, i);
__nvram_write_byte(c, i);
__nvram_write_byte(sum >> 8, PC_CKS_LOC);
__nvram_write_byte(sum & 0xff, PC_CKS_LOC + 1);
__nvram_write_byte(0, i);
__nvram_write_byte(*p, i);