[PATCH v2 0/2] rtc: provide an emulated RTC

[Heinrich Schuchardt]

On 10/29/20 11:27 AM, Pablo Sebastián Greco wrote:
> Can I suggest as a future enhancement adding an option to also be able
> to read U_BOOT_EPOCH from env? Userspace tools could write the time on
> shutdown (like fakehwclock).

Thank you for your suggestion.

What does fakehwclock relate to?

> Ok, adding `date xxxxx` to the start script could work too, but it seems
> messy.

If you have network, you should use CONFIG_CMD_SNTP=Y and
CONFIG_BOOTP_NTPSERVER=y and add "setenv autoload no && dhcp && sntp" to
your script.

This is why I submitted the following patch:

net: sntp: remove CONFIG_TIMESTAMP constraint
https://lists.denx.de/pipermail/u-boot/2020-October/430445.html

If we want to follow you idea, we would have a probe() and a remove()
method to the driver for managing the environment variable.

One problem with saving the time on shutdown to the environment is that
save_env() always saves the complete environment and not a single
variable. Saving the complete environment may save changes that you do
not want to persist.

So a complete solution will require:

* Create a function to save a single environment variable selectively.
  This will be the part with the biggest effort.
* Implement the probe() and remove() methods
* Add a Kconfig option to enable the usage of the environment variable.

But is this worth the effort if you have SNTP?

Best regards

Heinrich

>
> On 25/10/20 04:13, Heinrich Schuchardt wrote:
>> On a board without hardware clock this software real time clock can be
>> used. The build time is used to initialize the RTC. So you will have
>> to adjust the time either manually using the 'date' command  or use
>> the 'sntp' to update the RTC with the time from a network time server.
>> See CONFIG_CMD_SNTP and CONFIG_BOOTP_NTPSERVER. The RTC time is
>> advanced according to CPU ticks.
>>
>> v2:
>> 	more elaborate Kconfig message
>> 	adjust device name properties
>> 	use build time as initial time
>>
>> Heinrich Schuchardt (2):
>>   Makefile: provide constant with seconds since epoch
>>   rtc: provide an emulated RTC
>>
>>  MAINTAINERS            |  1 +
>>  Makefile               |  2 ++
>>  drivers/rtc/Kconfig    | 11 ++++++
>>  drivers/rtc/Makefile   |  1 +
>>  drivers/rtc/emul_rtc.c | 80 ++++++++++++++++++++++++++++++++++++++++++
>>  5 files changed, 95 insertions(+)
>>  create mode 100644 drivers/rtc/emul_rtc.c
>>
>> --
>> 2.28.0
>>