Tims Fastboot Tools

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This page has materials to support Tim Bird's presentation "Tools and Techniques for Reducing Bootup Time". This presentation was first delivered at the Embedded Linux Conference, Europe, in November of 2008.

safe_to_call_sched_clock.patch

This patch was used by Tim for several kernel versions, to address problems with the printk-times feature on ARM platforms. It is very simple, and consists of just adding a flag to avoid calling sched_clock() too early.

This patch appears (as of kernel version 2.6.27) to be obsolete. The 2.6.27 kernel now calls cpu_clock() for printk_times. This uses a similar mechanism to flag when it is safe to call.

Here's the patch:

On most platforms, printk_clock() calls sched_clock(), which provides good
timestamp resolution.  However, most ARM boards use a timer source for
sched_clock() which must be initialized at boot.  If sched_clock() is called
too early, the machine hangs. This code utilizes the default jiffies-based
value for printk_clock, until told that sched_clock() is safe.  This is
almost always 0 before the clock is initialized, so this patch causes
no loss of timing data, or confusing time switchover mid-boot.

OMAP support is included.  

To utilize this on other ARM platforms, just add "safe_to_call_sched_clock=1"
in the timer initialization code for your platform, when it is safe to call
sched_clock().

Signed-off-by: Tim Bird <tim.bird@am.sony.com>

ChangeLog:
    2008/02/05
    Location: alp@oak--linux-3/alp-linux--dev-3--3.1
    First changlog version.
---
 arch/arm/kernel/time.c      |    8 	7 +	1 -	0 !
 arch/arm/mach-omap1/time.c  |    3 	3 +	0 -	0 !
 include/asm-arm/mach/time.h |    2 	2 +	0 -	0 !
 3 files changed, 12 insertions(+), 1 deletion(-)

Index: alp-linux/arch/arm/kernel/time.c

grabserial

"grabserial" is a simple program to grab and display data from a specified serial port. It can place a timestamp on each line received, which makes it useful for reporting timing of events seen on a booting system's serial console output.

See Grabserial for detailed information, sample output and download instructions.