Specifications

14.3.25. Use NTP to synchronize system time
against RTC
If a system has a real-time clock (RTC) this is often used only to initialize the system time when the system
boots. From then, the system time is running independently. The RTC will probably only be used again at
shutdown to save the current system time. Such a configuration is used in many workstation configurations. It
is useful if time is not really critical, or if the system time is synchronized against some external reference
clock like when using the Network Time Protocol (NTP) to access time servers on the network.
But some systems provide a high-accuracy real-time clock (RTC) while the system clocks are not as accurate,
and sometimes permanent access to the net is not possible or wanted. In such systems it makes more sense to
use the RTC as reference clock (Stratum 1 NTP server - cf. http://www.ntp.org/). To enable this mode of
operation you must edit the NTP daemon's configuration file /etc/ntp.conf in your target's root file
system. Replace the lines
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 10
by
server 127.127.43.0 # standard Linux RTC
Then make sure to start the NTP daemon on your target by adding it to the corresponding init scripts and
restart it if it is already running.
The "address" of the RTC (127.127.43.0 in the example above) is not an IP address, but actually used
as an index into an internal array of supported reference clocks in the NTP daemon code. You may need to
check with your ntpd implementation if the example above does not work as expected.
14.3.26. Configure Linux for XIP (Execution In
Place)
This document describes how to setup and use XIP in the kernel and the cramfs filesystem. (A patch to add
XIP support to your kernel can be found at the bottom of this page.)
14.3.26.1. XIP Kernel
To select XIP you must enable the CONFIG_XIP option:
$ cd <xip-linux-root>
$ make menuconfig
...
MPC8xx CPM Options --->
[*] Make a XIP (eXecute in Place) kernel
(40100000) Physical XIP kernel address
(c1100000) Virtual XIP kernel address
(64) Image header size e.g. 64 bytes for PPCBoot
The physical and virtual address of the flash memory used for XIP must be defined statically with the macros
CONFIG_XIP_PHYS_ADDR and CONFIG_XIP_VIRT_ADDR. The virtual address usually points to the end
of the kernel virtual address of the system memory. The physical and virtual address must be aligned relative
to an 8 MB boundary:
14.3.26. Configure Linux for XIP (Execution In Place) 191