Linux Device Drivers Development

Reading and setting time

The driver is responsible for providing functions to read and set the device's time. These are the least an RTC driver can provide. When it comes to reading, the read callback function is given a pointer to an allocated/zeroed struct rtc_time structure, which the driver has to fill. Therefore, RTCs almost always store/restitute time in Binary Coded Decimal (BCD), where each quartet (series of four bits) represents a number between 0 and 9 (rather than between 0 and 15). The kernel provides two macros, bcd2bin() and bin2bcd(), to convert from BCD encoding to decimal or from decimal to BCD, respectively. The next things that you should pay attention to are rtc_time fields, which have some boundary requirements, and ...