[U-Boot-Users] CFG_HZ value

[Umar Quershey]

Hi,

Ok, so just to clarify:

If I run the following code on a 1GHz machine vs. a 300 MHz machine and
assuming that the read_reg always equals 0:

tmo = get_timer (0) + 1 * CFG_HZ;
while ((((read_reg(0xa6)) == 0)&& tmo < get_timer (0))
                /*NOP*/;


then the timeout should occur much quicker on the 1 GHz machine as
opposed to the 300 MHz machine.  The reason being that the timer will
decrement much faster on the gig machine (assuming the timer is fed the
system clock same as CPU).

Is this a correct analysis or am I missing something?  If true, then the
timeout has to account for the clock of the timer (rate of timer
decrement) which will not necessarily be CFG_HZ.  So in that case I'd
need to set tmo to something as:

tmo = get_timer(0) + 1 * clock_speed; /*clock_speed is timer clock in
MHz*/

Any inputs appreciated.

Regards,
Umar

-----Original Message-----
From: wd at denx.de [mailto:wd at denx.de] 
Sent: Wednesday, June 20, 2007 12:27 AM
To: Umar Quershey
Cc: u-boot-users at lists.sourceforge.net
Subject: Re: [U-Boot-Users] CFG_HZ value 

In message <87A697E50899F541B77272C331CEB744D502 at exchange.Q-DOMAIN> you
wrote:
> 
> How should one define CFG_HZ?  It seems that it's to be set to 1000.

Correct. Please consider CFG_HZ as a constant which has to be set to
1000 on all systems.

> However my system clock speed is not this.  What are the rules for

It has nothing to do  with  any  clock  speed,  like  the  time  unit
(seconds)  on  you  digital  watch  has nothing to do with the actual
clock of the quartz used somewhere in it.

> Should I replace the CFG_HZ with my real system clock speed?  BTW, I

No. CFG_HZ is always 1000.

> have to read a register at boot time to determine what speed I am
> running at.  I do this early on and save a variable 'clock_speed' that
> other functions can use to determine the system clock speed.

With correctly implemented timer functions it just works.

> ------_=_NextPart_001_01C7B2DA.91121226
> Content-Type: text/html;

Please never post HTML here.

Best regards,

Wolfgang Denk

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