This affects the detection of 24-hour vs AM/PM mode... the ampm bit is in a
different location on 2127 and 2129 chips compared to other nxp rtc chips.
I noticed the 2127 case wasn't being handled correctly when I accidentally
misconfiged my system by claiming my PCF2129 was a 2127.
on PCx2129 chips too.
The datasheet for the PCx2129 chips says that there is only a watchdog
timer, no countdown timer. It turns out the countdown timer hardware is
there and works just the same as it does on a PCx2127 chip, except that you
can't use it to trigger an interrupt or toggle an output pin. We don't need
interrupts or output pins, we only need to read the timer register to get
sub-second resolution. So start treating the 2129 chips the same as 2127.
An obscure footnote in the datasheets for the PCx2127, PCx2129, and
PCF8523 rtc chips states that the chips do not support i2c repeat-start
operations. When the driver was originally written and tested, the i2c
bus on that system also didn't support repeat-start and just quietly
turned repeat-start operations into a stop-then-start, making it appear
that the nxprtc driver was working properly.
The repeat-start situation only comes up on reads, so instead of using
the standard iicdev_readfrom(), use a local nxprtc_readfrom(), which is
just a cut-and-pasted copy of iicdev_readfrom(), modified to send two
separate start-data-stop sequences instead of using repeat-start.
The driver now ensures only one thread at a time is running in the API
functions (clock_gettime() and clock_settime()) by specifically requesting
ownership of the i2c bus without using IIC_RECURSIVE, then it does all IO
using IIC_RECURSIVE so that each individual IO operation doesn't try to
re-acquire the bus.
The other IO done by the driver happens at attach or intr_config_hooks time,
when there can't be multiple threads running with the same device instance.
So, the IIC_RECURSIVE flag can be safely ORed into the wait flags for all IO
done by the driver, because it's all either done in a single-threaded
environment, or protected within a block bounded by explict
iicbus_acquire_bus() and iicbus_release_bus() calls.
setting up the timer fails, because on some types of chips that's the
first attempt to access the device. If the chip is missing/non-responsive
then you'd get a driver that attached and didn't register the rtc, with
no clue about why. On other chip types there are inits that come before
timer setup, and they already print messages about errors.
generic driver with minimal feature support for a large number of chips.
More featureful per-chip drivers might exist (especially out-of-tree) and
those should win the bidding even if they use BUS_PROBE_DEFAULT.
between 12/24 hour mode. Also fix conversion between 12 and 24 hour mode.
It's not as easy as adding/subtracting 12, because the clock doesn't roll
over 11->0, it rolls over 12->1; 0 isn't a valid hour in AM/PM mode.
all the chips in the NXP PCA212x and PCA/PCF85xx series. In addition to
supporting more chips, this driver uses the countdown timer on the chips as
a fractional seconds counter, giving it a resolution of about 15 milliseconds.
