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The NXP PCF8563 is a battery backed I2C clock at the fixed address 0x51, common on RISC-V and ARM boards, and NuttX had no driver for it. The nearest part in the tree, the PCF85263, has a different register map. The driver follows the shape of the external I2C clocks already here, ds3231 and pcf85263: board logic calls pcf8563_rtc_initialize() once the bus exists, and the chip then answers up_rtc_getdatetime() and up_rtc_settime() for the system clock. Three behaviours are deliberate. The top bit of the seconds register means the oscillator has stopped since the time was last set, so every register after it holds whatever it stopped on. A read in that state returns -ENODATA rather than the contents: a caller told the time is unknown can act on that, one told a wrong time cannot. A flat backup cell and a clock that has never been set both arrive here. The top bit of the month register marks a century rollover, but which value means which century is a convention that parts disagree on, so no century is read from it. The chip is treated as a clock for 2000 to 2099, the bit is written back as it was read, and a date outside those years is refused rather than stored as one that would read back different. This is what the mainline Linux driver does. The counters are stopped across a write so a carry cannot land between the seconds and the minutes, and restarted even when the write failed, since the alternative is leaving the clock stopped. The alarm and countdown timer are not implemented; their registers are defined. Assisted-by: Claude:claude-opus-5 Signed-off-by: Justin Hammond <justin@dynam.ac> |
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