HelenOS sources

REG_RW_PORT       282 uspace/drv/time/cmos-rtc/cmos-rtc.c 	return pio_read_8(REG_RW_PORT(rtc->port));
REG_RW_PORT       295 uspace/drv/time/cmos-rtc/cmos-rtc.c 	pio_write_8(REG_RW_PORT(rtc->port), data);
HelenOS homepage, sources at GitHub