Update documentation

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>

README.md

@@ -7,3 +7,6 @@ service configuration and further, available services.
 
 See [docs/network.md](docs/network.md) for a description on how to do static
 network configuration with the provided script and service.
+
+See [docs/swclock.md](docs/swclock.md) for a description on the software pseudo
+RTC implementation for systems that do not have a hardware real time clock.

docs/defconfig.md

@@ -113,10 +113,6 @@ For the shutdown and reboot targets, the following services are executed:
    kernels clock from the hardware at bootup, between the `vfs` and `sysinit`
    targets.
  * nft - If enabled, restores net filter table rules during boot.
- * swclock - For systems that don't have a hardware clock, this service
-   restores a somewhat usable time from a file during boot.
- * swclocksave - For systems that don't have a hardware clock, this service
-   saves the current time to a file during shutdown or reboot.
  * sshd_keygen - A wait type service that generates host keys for the OpenSSH
    server and then disables itself.
  * sshd - Starts an OpenSSH server after the network pseudo service and after

docs/network.md

@@ -81,3 +81,14 @@ follows is passed on to `ip route add` or `ip rule add` respectively.
 
 An additional service is provided that restores the nft rule set from
 `/etc/nftables.rules`.
+
+
+# DHCP based network configuration
+
+If the configure option `--enable-dhcpclient` is set, two services are added.
+The service `dhpcdmaster` launches a global dhcpcd instance.
+
+For each port that should be configured via DHCP, the service `dhcpcd` needs
+to be enabled manually with the port name as argument. The service the runs
+after the master service and sends a signal to the master to operate on that
+port.

docs/swclock.md

@@ -0,0 +1,25 @@
+# Software Pseudo RTC
+
+If the configure flag `--enable-swclock` is set, a few service and cron jobs
+are enabled that try to help with systems that don't have a hardware real
+time clock.
+
+The software pseudo RTC uses a file in `/var/lib` (exact path can be
+configured) as backing store for the current date and time.
+
+When booting the system, a service called `swclock` restores the current time
+from the file. When performing a reboot or shutdown, a service called
+`swclocksave` writes the current time back to the file.
+
+A cron job is enabled that writes the current time to the backing file hourly,
+so in case the system momentarily loses power, it loses "only" up to one hour.
+The time will drift much worse anyway if the system is powered off (even
+intentionally) for a while.
+
+All this is ensures that the system clock is monotonically increasing and only
+somewhat behind the actual wall clock time.
+
+To catch up with real time, an additional cron job is enabled that tries to
+update the time from an NTP server every four hours. This functionality is
+implemented in a small shell script, that is also called from a dhcpcd hook
+once a lease is obtained, assuming the DHCP client configure option was set.